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Towards design and development of isothermal cloud chamber for seeding experiments in tropics and testing of pyrotechnic cartridge
Accepted Manuscript Towards design and development of isothermal cloud chamber for seeding experiments in tropics and testing of pyrotechnic cartridge P. Kumar PII:
S1364-6826(18)30133-0
DOI:
10.1016/j.jastp.2018.10.002
Reference:
ATP 4927
To appear in:
Journal of Atmospheric and Solar-Terrestrial Physics
Received Date: 22 February 2018 Revised Date:
30 September 2018
Accepted Date: 3 October 2018
Please cite this article as: Kumar, P., Towards design and development of isothermal cloud chamber for seeding experiments in tropics and testing of pyrotechnic cartridge, Journal of Atmospheric and SolarTerrestrial Physics (2018), doi: https://doi.org/10.1016/j.jastp.2018.10.002. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Towards Design and Development of Isothermal Cloud Chamber for Seeding Experiments in Tropics and
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Testing of Pyrotechnic Cartridge
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By
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P.Kumar,
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(NICRA Project, ICAR, Ministry of Agriculture, Govt. of India)
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Department of Mathematics, MIT-World Peace University, Pune.
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Email: [email protected],Phone: +919860705053
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Abstract
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Isothermal cloud chamber with capacity of 120x120x120 cm3 has been designed and developed for performing
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cloud seeding experiments in simulated tropical atmosphere. Purpose of the chamber is to test the efficiency of
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artificially generated IN (for cold region of the cloud) or CCN (for warm region of the cloud) agents, in simulated
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pressure, temperature or humidity condition as in natural cloud layers (levels). Level to level results can be
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subsequently tabulated together in sequence to view an integrated picture of the performance of the existing agent
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formulation in entire(simulated) natural cloud condition.
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Chamber pressure is designed to achieve up to 350 hPa and lower temperature is designed to get -250C. Controlled
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higher temperature in the cloud chamber is designed to reach ≥ +100C (even up to +500C). Humidity could be
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controlled in the range of 30% to 100 %. This isothermal chamber is designed primarily to test the seeding
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efficiency.
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Hypotheses used are;
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If the Lux meter reading at the time of release of IN is L0 and after 5 minutes# if it improves to L5 then
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If drop in luminosity is d and total concentration of particulate matters is Cp per unit volume then
If the Lux meter reading after 15 minutes# of the release of IN is L15 and after 30 minutes# interval if it improves to L30then
Rate of Nucleation (RN)*
α
Cp
(1)
α
L5 - L0
(2)
α
L30 - L15
(3)
(*It includes condensation and Ice nucleation both)
Rate of Precipitation (ROP)
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(# Broad chronological classification)
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The hypotheses are reasonably valid for small size of droplets (≤ 20 µm). For the solid phase or mixed phase of the
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droplets further examination is needed to apply correction factor. Loss of moisture due to deposition on wall is
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incessantly replenished by the humidity controller to simulate nature. Incessant growth in the luminosity-drop only
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indicated the active process of nucleation and subsequent growth in size of particles. The faster the process the
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higher is the efficiency of the seeding agent.
27 It was found that the optimal range of atmospheric temperature and pressure for effective cold region seeding is -
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3.70C to -190C. Entire process of condensation growth and precipitation takes place only ≈ 30 minutes within the
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chamber.
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6th order polynomial successfully simulates the spontaneous condensation process for simultaneous variation of
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pressure and temperature with very high coefficient of determination.
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Keywords. Cloud Chamber, Rate of Condensation, Rate of Precipitation, Quantitative measurements of aerosols,
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lux meter
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1.0 Introduction
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Various types of cloud chambers have been developed as apparatus for different types of experiments in several
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disciplines of science and engineering. Wilson’s original cloud chamber, initially developed in 1912, was a glass
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cylinder, about 16 cm across and about 3 cm deep. Its walls were coated in gelatin, with the base dyed black for a
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photographic dark background. The floor of the chamber was fixed to the top of a brass plunger. It all stood in a
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shallow trough of water that kept air in the chamber saturated with water. A diaphragm was used to expand the air in
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the chamber for adiabatic expansion, cooling the air and starting to condense water vapor. This kind of chamber is
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called a pulsed chamber because the conditions for operation are not continuously maintained. Wilson Cloud
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Chamber which provided adiabatic expansion (Das Gupta and Ghosh -1946;Matteo and Nadia , 2004) became a
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fundamental tool of research not only in atmospheric science but also in nuclear, cosmic ray and elementary particle
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physics. The close examination of the expansion apparatus, the illumination method and the photographic method
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showed that the cloud chamber is a fine example of experimental ingenuity. Cloud Chambers for weather studies
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have been described by Grant and Steele (1966), and Garvey (1975). Colorado State University(CSU) modified
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Garvey’s chamber known as CSU Isothermal Cloud Chamber (ICC). Advance features e.g. Particle Measurement
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Systems, dew-point and airflow calibration installation of an acoustic sensing ice crystal counting device were
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introduced in ICC(DeMott,1982).
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Cloud Chambers are used for various types of testing e,g, prototype evaluation, reliability testing, failure analysis
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and many other application where environmental simulation is needed. Cloud Chambers are aimed to simulate
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virtually any type of environmental condition such as temperature, humidity, altitude, solar, wind & rain, dust, etc.
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Various sizes of cloud chambers are available ranging from small bench-top chambers to large living room size
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chambers for cloud seeding experiment purpose. They provide temperatures range from -40°C to +50°C wherein the
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optional humidity could be controlled from 10% to 95% and different pressures to simulate atmospheric conditions.
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There are various kinds of cloud condensation nuclei/Ice nuclei chambers for performing experiments with different
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cloud seeding agents (Kumar 2017). With an objective to help seeding campaigns, in the present paper an attempt
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has been made to design and develop a simpler and cheaper isothermal cloud chamber for testing the efficiency of
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any pyrotechnic cartridge - releasing IN agents in cold cloud regime - or that of any CCN agents in warm cloud
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regime. Later could be released either by dispersion of finely ground particles or sprayed through atomizer as
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droplets, from a brine solution.
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1.1 Some definitions in context of atmosphere.
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Particulate matter: Particulate matter is the term used for all solid particles suspended in air. Aerodynamic size (effective diameter de) of a particle of less than 10 µm, 5 µm and 2.5 µm are known as PM10 PM05 and PM2.5 respectively. EPA, U.S.A.2017 b) Nucleation: Any process by which the phase change of a substance to a more condensed state (condensation, sublimation, freezing) is initiated at certain loci within the less condensed state. AMS, 1952; McDonald, 1953; Mason, 1957. c) Heterogeneous nucleation: Nucleation loci are particles which exist in different, almost invariably more condensed initial state than the condensing or freezing matter. The particle may be of the same substance as that which is changing state. AMS, 1952; McDonald, 1953; Mason, 1957.
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d) Homogeneous nucleation: It occurs when the change of state centers upon loci which exist in the same initial state as the changing substance. In this case the nucleation system contains only one component and it is termed as spontaneous nucleation. AMS, 1952; McDonald, 1953; Mason, 1957. Reaction Time: Time duration taken by the cumulus cloud to turn into hailstorm (Kumar and Pati, 2015; Kumar, 2017). Total Reaction Time (TRT) is defined as the time taken by any growing cumulus cloud from reflectivity of 20 dBZ to 45dBZ. Available Reaction Time (ART) is the time actually available within the TRT for seeding campaign for Hail mitigation.
At low super saturations, heterogeneous nucleation will be dominant, and at high super saturations, homogeneous nucleation will occur (Chemov, 1984; Skripov, 1977; Sohnel, 1978;Colin and Wagner, 2007; Pruppacher and Klett, 2010).
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1.2 Need for efficient seeding agent and optimum Temperature and Pressure regime. A seeding agent which is quick and effective is an efficient seeding agent. Garvey(1975)had defined effectiveveness as number of ice nuclei active at a given temperature per gram of nucleant burned and is determined in the manner similar to that described by Vonnegut(1949). Quickness is needed due to limitation of reaction time and effectiveness demands suitable environmental conditions for the seeding chemicals for optimum results e.g. suitable environmental temperature and pressure. While time limitation is a constraint in several weather modification activities e.g. rain increase, fog dispersal etc., it has high significance during hail mitigation campaigns due to the limitation of Reaction Time (refer 1.1g). Reaction time could be less than 90 minutes. Hail mitigation measures need massive seeding of cloud before hail has formed (Kumar, 2017). Also if the seeding nuclei are not delivered in the suitable temperature and pressure range results could be unsatisfactory. Effectiveness of seeding agent is the number of ice nuclei active at a given temperature per gram of nucleant burned (Vonnegut, 1949). During Alberta hail project Summers et al, 1972 had noted strong temperature dependence of effective nuclei per gram of AgI burning. Number of effective nuclei at -50C were 8x1010 whereas it rapidly rose to 4x1015 at -200C. Superior performance near -50C of acetone generators contained with AgI-NH4I solution is generally recognized in laboratory and field experiments(Dennis, 1980). Hence quick transportation and delivery of seeding agents and their quick response after they are ingested into cloud to produce precipitation, is most important in hail mitigation (ASCE, 2015). This chamber is, therefore, designed not only to test the effectiveness of the CCN or IN agents under different environmental conditions but also to develop the efficient pyrotechnic cartridge (cold cloud seeding) which is capable of producing smoke in shortest possible time. For cold cloud seeding experiments, desired subzero cloud environment may be simulated in the chamber. Fig. 1(a)
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Fig. 1(b)
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Similarly warm region of the cloud can also be simulated in the chamber by fixing its temperature and pressure
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equivalent to any level of warm region of the cloud, along with ≈ 100% humidity. Thus warm cloud seeding agents
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e.g. NaCl dust dispersion or brine solution atomizer, may be tested in the chamber.
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In the present paper design and full size fabrication (refer fig. 1) of a cloud chamber is presented for performing
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various experiments of cloud seeding with different chemicals. In tropics as the base pressure level of the cloud
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could be 900 hPa or more and cloud top could be 200-150 hPa or less, the cold seeding or warm seeding could be
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planned separately as per the actual atmospheric level. For achieving near vacuum state within chamber the pressure
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can be brought down up to 267 hPa. Lower temperature could be controlled up to -250C. 0
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Further as base
temperature of the cloud in tropics could be ≈ +10 C or more (± 3 C) hence controlled higher temperature in the
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cloud chamber is designed to reach ≥ +100C . Humidity could be controlled in the range of 30% to 100 %( ± 3%).
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Arrangements are made to introduce pyrotechnic cartridges system which will burn and generate plumes of silver
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iodide for the cloud seeding purpose. There is also arrangement to introduce the finely ground (effective diameter ≈
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< 5µ), warm cloud CCN agents (e.g. NaCl, CaCl) dust particle as well as there is one nebulizer provided to spray
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solution droplets (< 5µ), with in the chamber. The chamber is also attached with steam generation unit (electrical
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heating system) so as to maintain controlled humidity (RH) at any level between 30% up to 100%.Special care has
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been taken so that electrode surfaces are perfectly sealed and are not exposed into chamber to ensure no charge
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transfer into steam or chamber atmosphere.
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The chamber has been designed with objective to test the efficiency of seeding chemicals in warm or cold cloud
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conditions. It assesses the degree of opacity of the cloud through lux meter and unlike chamber by DeMott(1982) no
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particle counters or particle size measurement instruments are separately installed. Lux meter is relatively much
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cheaper equipment than expensive particle counter. With 1 µm pinhole diameter the (extinction correlation value is
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≈ 1; Korolev, et al., 2012) the aberration due to size variability is negligible (explained in section 2.1). Lux meter
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(accuracy ±1 Lux) is installed inside the chamber to qualitatively sense cloud formation in the chamber and its
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subsequent disappearance, as cloud droplets gradually transform into drizzle, rain or hydrometeor and fall on the
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chamber floor. The lux (symbol: lx) is the SI derived unit of luminance and luminous emittance, measuring
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luminous flux per unit area. It is equal to one lumen per square meter. In photometry, this is used as a measure of the
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intensity, as perceived by the human eye, of light that hits or passes through a surface. Chamber is equipped with
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LED light source to help camera to spontaneously display chamber occurrences on the computer digital screen
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outside.
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Theoretical principle of cloud chamber is described in section 2. Descriptions of various hardware are presented in
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section 3. Method of making a pyrotechnic cartridge with specific formulation has been described in section 4.
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Experimental details of testing of pyrotechnic cartridge in the cloud chamber and analysis of results are presented in
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section 5. Section 6 concludes the paper. Appendix-A describes the testing of 10 different cartridges with slightly
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varying formulation which were tested in the cloud chamber. Lux meter readings, for all ten cartridges in Appendix-
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A, at 0, 5, 10, 15 and 30 min intervals, were taken. The formulation which indicated quickest nucleation and
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quickest precipitation was selected as best formulation of cartridge for experiments.
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2.0 Principle of Assessment of Cloud and Precipitation within cloud Chamber
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Refer schematic line diagram in fig. 2. Fig.2
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Lux meter is installed in the cloud chamber with its pinhole source of light (LS) on the inside left panel of the
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chamber wall and its receiver (LR), is installed on the inside right panel of the chamber wall, directly opposite to
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source of light. Beam from LS travels across the chamber’s width (120cm) and reaches the receiver LR. Illumination
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received at LR is digitally displayed on the screen (VD) fixed outside the chamber. The lux meter is calibrated in
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such a way that when there is no interference or obstruction for the beam then it displays 250 lx (250 Lux (lx) =
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371.6 Candela (cd) for 120 cm distance). If there are beam obstructions by particulate matters or liquid droplets and
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if the received illumination at LR is LRC then the drop (d) in illumination from 250 lx is given by d = 250 – LRC. If
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total concentration of total nuclei, cloud and precipitation hydrometeors between Ls and LR is Cp per unit volume
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then we can assume that
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d
α
N(Number of condensed, frozen or mixed nuclei or embryos between LS and LR)
α
s (Cross section area of each particulate matter between Ls and LR)
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Equation (1) may be combined as
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d
α
KNs
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(1)
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(1.1)
Where K is the chamber-constant for the specific cloud chamber and equals to Q (I0/S0) where Q is the total photo
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extinction efficiency of nuclei plus photo extinction efficiency of supercooled and non supercooled droplets, I0is
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incident light intensity and S0 is the uniform cross section of the cylindrical beam from LS to LR.
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Cp therefore is defined as the net water mass per unit volume in liquid phase or solid phase or mixed phase between
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LS and LR (Korolev, et al., 2012).
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Hence for the cloud chamber we can hypothesis that
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d
Cp
(1.2)
The hypothesis can be explained by the Beer-Bouguer law as
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I = I0 e - β(ʎ) L
(2)
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Where I0 is incident light intensity I is light intensity transmitted through the medium in the forward direction (i.e.,
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parallel to the incident light),β(ʎ) is volumetric extinction coefficient at wavelength ʎ, and L is geometric distance
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between emitter and receiver which is 120 cm for this cloud chamber. If we consider the Beer-Bouguer law in the
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differential form for a medium consisting of mono disperse particles with the concentration n and thickness dx, 5
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dΙ = σnΙ0 dx
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(3)
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scattering cross-section of one particle; s is the geometric cross-section of the particle; and Q is the extinction
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efficiency. The particle concentration n can be presented as n = dN/dV = dN/(S0 dx) where dN is the particles in
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volume dV and S0 is the cross section of the beam from LS to LR
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Then
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Left hand side of eqn. 4 is the drop in intensity after the light beam traverses a distance dx. Combining eqn.4 with 3
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and integrating for spatial rate of change of dN from x= 0 to x= L (=120 cm) we get
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LRC - Ls
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Q and s are variable but for small particles (≤ 20µm) the extinction efficiency (Q) may be assumed to be constant for
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pinhole source of light. It is discussed in section 2.1, in detail. When chamber is not having any super cooled cloud
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droplet or ice crystal its luminosity is indicated as ≈ 250 Lux (explained in later part of this section and in
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Appendix-A).It is pointed out that display of 250 lx prior to experiment is due to aggregate of LED in the chamber
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and in situ ambient atmospheric aerosols, rudimentarily left inside, despite the lowest pressure achieved after the
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suction. Once the cartridge is burnt it releases several nucleating agents. Those which nucleate will grow and fall
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down but at the end smoke particles, generated due to burning of cartridge casing may not nucleate and will still
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remain suspended. They would continue small degree of interference(due to smaller size) and hence after each
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experiment the luminosity would not revert back to exactly 250 but would be little less than 250 Lux(LS<250). But
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the drop in luminosity will be caused by those particles which have nucleated and fell down. We are concerned with
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nucleated particles not those which do not participate in nucleation; Hence we can have
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250 – LRC (Since LS≈ 250 Lux) d
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The higher the drop in illumination on LR from its highest value (≈ 250 Lux), the higher is the concentration of
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liquid droplets or solid aerosols or cloud /precipitation droplets, in the cloud chamber, filling the space between the
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source (LS) and the receiver (LR) of Luxmeter. Therefore formation of cloud/precipitation could be directly related
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to drop (d) in illumination from 250 Lx.
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Ls transmission is through circular pinhole of diameter is 1µm. Ab-initio reading of ≈ 250 lux meter prior to release
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of any IN is net luminosity which is the sum total LED and in-situ aerosols as permitted by the filter, prior to the
Qs (dN/(S0 dx)) I0 dx
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Qs dN I0/S0
(4)
= Cp; I0/S0 being constant.
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α Total concentration of nucleated particulate matters i.e. Cp
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experiment. Once ensemble of INs are released the super cooled droplets or ice crystals will have size not less than
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size of IN. Hence 1µm is the lower limit for all the subsequent droplets or ice crystals during the progress of
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experiment. As per the manufacturers specification the Lux meter installed in the cloud chamber can operate for a
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wide range of luminosity varying from 0 to 2000 lux with the least count accuracy of 1 lux but chamber has one
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LED source installed for visualizing the chamber operations on a display screen of computer kept outside the
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chamber. Hence cloud chamber is never totally dark. When chamber is not having any cloud particles its luminosity
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is indicated as ≈ 250 Lux. This is as per the illumination of the chamber provided by the LED light source and is
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totally independent of temperature, pressure and humidity. Also when the chamber is full of cloud droplets, the
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lowest lux meter reading at very low temperature and pressure, during best seeding results, showed ≈10 Lux. Both
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these values are cloud chamber specifications. Hence the instrumental operational limits of the lux meter in the
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cloud chamber ranges from 10 to 250 Lux. For each gram of seeding substance in the pyrotechnic cartridge the
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resulting smoke may generate IN in the range of 1010 to 1016 nuclei. Nevertheless the count depends on temperature
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pressure and humidity of chamber. This estimate is based on the chamber particle counters from De Mott (1982). On
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an average it could be 1014(Rogers and Yuan, 2006). It can vary based on the design of the chamber(Edwards and
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Evans,1960).
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Improvement in the Lux meter reading is independent of the type of process of rain formation, i.e. may it be
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Precipitation process by Wegener - Bergeron - Findeisen process or ice crystal process and/or by collision –
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coalescence (Mahen et al 2012) or may it be both the processes together followed by Rain or drizzle droplets could
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get deposited either on chamber side walls or fall on chamber ground or remain suspended anywhere within the
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empty chamber space.
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2.1 Does particle size influence the Lux meter reading?
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In general it is known that forward scattering by particles is likely to introduce errors in the observed ‘LRC ’ value in
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eqn.5. Mie scattering calculations show that forward scattering is relatively weak for small particles (de< 10 µm; de
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is effective diameter), and so in the case of small droplets. Unlike natural conditions in a laboratory cloud chamber
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due to limited freedom of movement within limited space, the cloud particles are unable to grow to large natural
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drizzle or rain size, although they still precipitate and fall as relatively much smaller droplets. Fukuta (1969) had
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measured the size of fog droplets after artificial seeding in a cloud chamber. All the droplets were less than 20 µm
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in diameter and out of them mostly (≈ 80%) were less than 10µm in diameter. Hence particles (de< 10 µm) will
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not cause any significant error albeit some error is likely by larger droplets (>20µm).This needs to be further
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examined.
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Reliability of equation 1.2 is inherent in the correct value of ‘d’ which is guided by LRC value. Korolev, et al.,
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(2012) had noted that any possible aberration in the value of LRC would depend on the stability of volumetric
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extinction coefficient (β(ʎ)) at wavelength ʎ. β(ʎ) depends on size and phase of the particle. They had shown that
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β(ʎ) = β0(1 – f) where β0 is the absolute extinction coefficient without any forward scattering. Parameter f (0≤ f ≤1)
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characterizes the forward scattering due to variation of size. Results of Korolev, et al., (2012) are shown in Fig. 3. It
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shows th e e xtinction correction values ‘1-f’,as determined by Monte Carlo simulation (heavy lines)and by
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Korolev, et al., (2012) in light lines, for water spheres and various pin-hole aperture sizes(as listed on the plot)as
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functions of particle diameter D. It is known through wind tunnel studies that a droplet of diameter smaller than
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140 µm had, within the experimental error no detectable deformation from spherical shape, Pruppacher and
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Beard, 1970. The smaller is the diameter (lesser than 140 µm) the more is the spherical shape of the droplet.
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Fig. 3
It is observed that for small size droplets (≤ 20µm) the extinction correlation value is ≈ 1 for pinhole size beam
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diameters as shown on the fig. 3. The smaller is the hole the better is the stability of extinction coefficient.
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Korolev, et al., (2012) results are valid for liquid droplets but uncertainty prevails for the solid phase or mixed
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phase of the droplets. Further study and experimental verification is needed for applying the exact correction
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factor
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2.2 Selection of time of observation for Rate of Condensation and Rate of Precipitation.
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Jonathan et al (2007) had noted that optical spectroscopy can provide a strategy for the direct assessment of particle size, composition and phase. Spontaneous Raman scattering can allow the unambiguous identification of chemical components and the determination of droplet composition. Stimulated Raman spectroscopy can allow the determination of droplet size with nanometre accuracy and can allow the characterization of near-surface composition. When combined, the mixing state and homogeneity in droplet composition can be investigated. The drop in luminosity(d) is the result of scattering from the condensed, frozen or mixed nuclei or embryos between LS and LR hence it may be possible to extract an estimate of the 'chemical signature' related to the seeding. With the back-up of its chemical signatures it may be stated that the lower the initial Lux meter reading the higher is the efficiency of IN of specific composition. Fukuta (1969) had also observed that within 12 seconds after seeding in the cloud chamber the fall velocity of all the hydrometeors were more or less same regardless of the temperature of super cooled fog. This is the period before marked growth habit differences start to appear. As they grow in size their fall velocity will depend on their size, phase and the temperature inside the chamber. Equation of motion (Wang and Pruppacher, 1977) of water drop of mass m is
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(6)
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Where V is the instantaneous velocity of the drop, t time, a the radius of the drop, ρw the density of water, η and ρ
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are the dynamic viscosity and density of air, respectively, FD is the drag force on the drop, g is the acceleration due
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to gravity, CD = 2 FD / πa2ρV2is the drag force coefficient of drop and NRe = 2aρV/η is the Reynolds number of the
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drop. The equation has to be solved numerically for CD and NRe are functions of V. But for small drops falling in the
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Stokes regime CDNRe/24 = 1 hence integration of resulting linear equation gives,
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(7)
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Where VT is the drop’s terminal velocity. Thus viscous relaxation time τs for spherical drop falling in Stokes regime
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is
(8)
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As temperature decreases from -50C to -200C the relaxation time increases from 1.299x103a2 to 1,361x103a2. Where
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m is mass of the droplet, a is radius of drop in cm, ρw is density of water. It is very small time interval for a droplet
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to reach its terminal velocity. Fukuta(1969) observed that between the temperature range of -50C to -200C, after 45 –
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50 seconds of growth the terminal velocity of falling particles in cloud chamber were 2 to 4 cm/sec. Broadly with
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this fall velocity itself any particle will take about 30 sec to 1minutes to travel a distance of 120 cm(inner height of
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chamber) under calm wind conditions. But due to continuous stirring of the cloud volume inside the chamber a
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broad cut-off time of 5 min was adopted during the experiment as condensation dominant period. Though it is
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practically impossible to determine as to when condensation slowed down to insignificant level (after complete
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burning of cartridge) and when pure droplet-growth by coalescence or Bergeron process and subsequently by Hallet-
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Mossop process (temperature range -30C to -80 C) took over (Hallet and Mossop, 1974). In fact all these process
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(e.g. nucleation and growth) may be expected to carry on after 5 min too, albeit nucleation rate will slow and its
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magnitude is expected to be significantly less whereas growth of droplets are certainly expected to sustain. Bergeron
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process or coalescence process or both types of precipitation formation are expected to remain functional during the
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entire period till d ≈ 0. As the cloud droplets are regularly growing in the chamber, hence any period during the
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improvement phase of Lux meter reading could be selected to determine the rate of precipitation. However to ensure
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that the process of precipitation strongly dominated the nucleation process on safer side one could take second half
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of the total period of improvement (back to ≈ 250 Lux) for the assessment of rate of precipitation. It could be
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assumed that by that time most of the CCN/IN released in the cloud chamber got converted into cloud droplets. We
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may call the time interval after 15 minutes as the precipitation phase.
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Hence we named ≤ 5 min as the nucleation phase (Phase –I), 5 – 15 minutes as the transition or mixed phase (Phase-
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II) and 15 – 30 minutes as the precipitation phase (Phase-III). This is a broad classification for the present chamber
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volume as temporally the processes would depend on the composition of the nuclei introduced into the system, the
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chemistry of the system, and the meteorology of the system, and the effect of the release of latent energy resulting
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from the ingested seed nuclei.
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2.3 Hypotheses of Rate of Nucleation and Rate of Precipitation
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Process of nucleation begins spontaneously (within ≈ 10 milliseconds; Kumar 2017) after release of AgI IN (Icing
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Nuclei). Precipitation process by Wegener - Bergeron - Findeisen process or ice crystal process and/ or by collision
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–coalescence (Mahen et al 2012) for cold cloud is also expected to begin immediately after the cloud formation
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within the chamber vis-à-vis improvement in the Lux meter reading. As the process of nucleation has to precede the
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rain formation short interval following release of AgI IN could be identified to determine the spontaneous Rate of
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Nucleation (RN) during which process of condensation, freezing and sublimation dominated the process of
313
precipitation. During all the experiments inside this chamber-volume it was observed that from the time of release of
314
IN the ‘d’ value tends to reach zero within about 30 minutes; may it be warm cloud/cold cloud environment.
315
Influence of chamber design over the apparent activity of silver–iodide in cold chamber was also noted by Edwards
316
and Evans (1960). IN particle results by different formulations of pyrotechnic cartridges are shown in Appendix-A.
317
Reversal of luminosity back to ≈ 250 level after the completion of experiment is the testimony that all the released
318
nuclei nucleated, grew in size and fell down by gravity. Abundant supply of moisture and limited period of
319
nucleation is the reason for it.
320
Warm cloud seeding devices are shown in fig.1(a)(b) in the upper part of the chamber. Natural environment with
321
respect to pressure, temperature and humidity (≈100%) of any desired warm levels between LCL to 00C of the cloud
322
can be simulated in the chamber and efficiency of CCN agents may be tested. During Cloud Aerosol Interaction and
323
Precipitation Enhancement Experiment(CAIPEEX) in India Mahen et al, 2012, found that in monsoon clouds over
324
indo-Gangetic plains the precipitation were initiated as super cooled raindrops at a temperature of – 80C. To
325
experimentally ascertain if the combined seeding of IN and CCN might have any adding affect over condensation
326
and precipitation process, lower levels in cold region may be simulated in the chamber and simultaneous or separate
327
seeding by pyrotechnic cartridge and NaCl dust or atomized solution may be conducted in laboratory.
328
In the isothermal chamber under the near saturation or super saturation of humidity at any temperature cloud
329
condensation or ice nucleation would take place spontaneously after the release of the IN. This initial condensation
330
or ice nucleation can be defined as spontaneous Nucleation. Spontaneous nucleation divided by duration of time is
331
defined as spontaneous Rate of Nucleation (RN). As initial 5 minutes after the release of IN could be assumed to be
332
dominated by the nucleation process hence if the Lux meter reading at the time of release of IN is L0 and after five
333
minutes interval if it is L5 then it may be hypothesized that
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Rate of Nucleation (RN)
α
L5- L0.
(9)
335
Validity of eq. (9) for cloud chamber is explained in sec. 2.1 and 2.2. Eq. (9) can extract the efficiency of chemical
336
signature of any IN agent. The higher the value of Rate of Nucleation, the higher is the effectiveness of IN released
337
in the chamber in rapidly producing ice crystals from water vapour.
338
If the Lux meter reading after 15 Minutes of the release of CCN’s is L15 and after 30 minutes interval if it is L30 then
339
it may be hypothesized that
340
Rate of Precipitation (ROP)
α
L30- L15
(10)
341
Eq. (10) can give the assessment of rate of the precipitation process within the chamber to a reasonable accuracy.
342
The higher the ROP the faster is the process of precipitation. Advantages of the assessment schemes hypotheses 10
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343
mentioned in eq.s(1), (9) and (10) are that they are independent of the profile of change in luminosity with respect to
344
time, may it be linear or non-linear and also it doesn’t require expensive particle counter equipment. Luxmeter is
345
much more economical.
346
Based on the hypotheses (1), (9) and (10), in the present chamber volume, RN and ROP can be defined as, below; (i)
and that at 5 minute (L5) as = kc (L0 – L5) gm/sec; where kc is proportionality constant (gm/Lux. sec).
348 349
Rate of Nucleation (RN): It is defined with difference between the Lux meter reading at 0 minute (L0)
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(ii)
Rate of Precipitation (ROP): It is defined as kp (Lt – Lt’) gm/sec; where kp is proportionality constant
350
(gm/Lux. sec). t and t’ in phase –II are 5 minutes and 15 minutes and in phase – III 15 minutes and 30
351
minutes respectively.
It may be noted that above hypotheses are specific for the volume of present cloud chamber - having capacity of
353
120x120x120cm3. Author feels that independent examination of corresponding hypotheses with different ‘chamber
354
size’ and ‘time frame’ might show path of miniaturization of atmospheric processes in space and time.
355
3.0 Description of cloud chamber
356
Fig1(a), Fig1(b) show the outer and inner view of cloud chamber. Fig1(a) is the look of cloud chamber when the
357
door is closed.In Fig.1(b)-Left the inside view of the cloud chamber is shown. Right-top is the NaCl powder
358
dispersion unit. It has fan inside for blowing the powder out of mesh (several hole of diameter = 1.0 cm) into the
359
chamber. Right-middle is the NaCl nebulizer unit which produces spray of NaCl droplets for seeding. Powder
360
dispersion unit and the nebulizer unit both are kept on the same platform as per the need of experiment. Right-
361
bottom is the pyrotechnic cartridge burning stand under the canopy. Horizontal pipe holding it has the electric wire
362
for triggering the fire through the nicrome wires connected to cartridge. Electrical wiring in the pipe is thoroughly
363
insulated to ensure no charge transfer to pipe casing. Small nicrome wire in the cartridge produces momentary
364
spark to trigger the burning then switches off the electrical current. During rest of the period the cartridge burns
365
by itself. This scheme ensures that there is no charge transfer to chamber aerosols. Schematic line diagram of the
366
cloud chamber (fig.2) gives the overview of the locations of Pressure Controller (Vacuum Pump-VP), Temperature
367
Controller (Refrigeration system- e.g. Air Compressor (AC) and other systems) and Humidity Controller
368
(Evaporator - E) in the cloud chamber. There is one circulator fan (C) provided on the back panel of the chamber for
369
maintaining the uniformity of atmospheric density distribution within the chamber space. Due to continuous air
370
circulation every volume element in the chamber has same humidity, temperature and particle density albeit particle
371
size may be variable at any space. To ensure uniformity in size of particles a prior size ranging is done after milling
372
of powder in a separate particle size analyzer. Fig. 2 shows three sensors for Humidity (HS), Temperature (TS) and
373
Pressure (VS). Near bottom of the chamber Pyrotechnic Cartridge Holder (PTCH) is fixed with a canopy for
374
performing experiment simulating cold cloud region. Canopy is provided as a shed for the burning flame of the
375
pyrotechnic cartridge so that any falling droplet does not extinguish it and also to quickly widen the dispersion of the
376
smoke generated by the burning cartridge so that it accelerates the quick distribution of the smoke particles
377
throughout the chamber space. There is one circular dry salt container(S) on the upper side of the chamber. The side
378
walls are 8 inch high, made of large size mesh – large enough to avoid any clogging (holes of 1.0 cm size diameter).
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There is one fan provided on the top of the container so that NaCl dust could rapidly be blown away through the
380
holes into the chamber while performing experiment, simulating warm cloud region. For the spray of brine solution
381
droplets in warm cloud region a Nebulizer (N) is provided close to salt container to spray droplets of nozzle size of
382
5µm or 10 µm as desired. Also there are intake filters provided at the inlet point of the air (AF). Chamber is
383
designed in such a way that desired pressure, temperature and humidity could be set initially only by the control
384
buttons provided on the front panel (right side) of the cloud chamber. Corresponding sensors would keep on
385
monitoring the parameters till they stabilize to desired values. Brief descriptions of different parts are presented
386
below in order of their experimental priority.
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3.1 Filter.
387
Filter is important component of cloud chamber. Several phenomena, e.g. inertial effect, diffusion, interception,
389
electrostatic, gravity, thermophoresis effect and Van der Waals force, etc., are commonly used to design filters.
390
First three of these, predominantly govern filtration mechanism. Nano fibres made of composites of glass, quartz,
391
nylon, silicon or silk polyester are used to make these high grade filters. Transparent Polyacrylonitrile fibres are
392
also used. Rectangular woven ‘nano-fibre mesh-sheets’ are obliquely joined in series to achieve the desired pore
393
size, in microns (Liu et al., 2017). In the present cloud chamber only filters of 1µm, 3 µm and 5 µm are installed.
394
Before the chamber is subject to any experiment it has to be ensured that the in-situ atmospheric aerosols are
395
removed so that they do not interfere in assessing the results of artificially introduced CCNs. Hence prior to
396
experiment, reasonably good degree of vacuum (as100% vacuum is not practically possible) needs to be generated
397
in the chamber by sucking out most of the chamber air. For this purpose a partial vacuum of 267hPa is generated in
398
the chamber. After this stage pressure in the chamber is increased to desired pressure level (e.g. 350 or more) at
399
which experiment is to be performed by intake of air through filters. As three filters of 1µm, 3 µm and 5 µm are
400
provided in the chamber hence if the experiment is to be performed with nucleating agents of sizes >3 µm or >5 µm
401
or >7 µm then filters of sizes 1 µm or 3 µm or 5 µm respectively, are to be used.
402
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3.2
Pressure Controller (Vacuum Pump)
404
Two heavy duty membrane pumps capable of continuous operation up to 30 days are installed with capacity of 100
405
liter with switch over function. Chamber is totally sealed with silicon fiber rubber seals on the main door panel and
406
double welding on the corners. It achieves lowest pressure of 200 mmHg (267 hPa). At the time of experiment pump
407
has to be stopped or else it would suck out the artificially released, CCN or IN from the chamber. Although all
408
precautions against leakage have been taken but despite that at very low pressure, due to strong inward pressure
409
gradient, after the motor is stopped, very slow inward air leakage remains unavoidable and the pressure gradually
410
increases at the rate of 30mmHg/Hr or (40hPa/hour). It is not clear that after motor is stopped what could possible
411
passage for the air entering the chamber to increase the pressure at very low pressure. Nevertheless possibly there
412
could be only two inlet/outlet. Either it could be the filter valves or it could be the suction pump valves, though both
413
of them are tightly closed as the motor is stopped. Hence it could be the mechanical limitation of the chamber.
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414
Any possible aerosol leaking along with the atmospheric air entering the chamber could be ignored as the aerosol
415
generations by the cartridges are of the order of 1010 to 1016 per m-3 for each gram of solution as observed in the
416
chamber of De Mott, 1982. In our chamber, too, same order of nuclei could be presumed which is expected to be
417
predominantly of very high order than the ambient aerosols which might possibly get sucked into chamber along
418
with
419
As any seeding experiment in the chamber does not last more than 30 minutes (Appendix A) from the time of
420
release of the CCNs till the luxmeter reading reverts back to ≈ 250 lx hence it reasonably meets the accuracy
421
requirements for seeding test experiment.
422
Rate of pressure increase after the motor is stopped is not same for all the pressure gradients. The lower is the
423
pressure the higher is the leakage rate. Between 300 to 400 hPa after the motor is stopped pressure rises at the rate of
424
≈40 hPa/hr, between 400 to 500 hPa it rises at the rate ≈20 hPa/hr and between 500 to 600 hPa rate of rise of
425
pressure further reduces to ≈ 10 hPa/hr. Below 600 hPa even after the motor has been stopped there is no pressure
426
increase displayed by the chamber and it remains steady. Highest rate of rise, therefore, is of the order of ≈40
427
hPa/hr. Hence within 30 minutes of experiment the rise of pressure would be of the order of ≈20 hPa only.
slowly
leaking
in
at
very
low
pressure.
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Temperature Controller(Refrigeration)
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Refrigeration system can achieve controlled temperature in the range from -250C to +500C with prescribed limit of ±
431
30C of stability. Environment friendly refrigerant(R-404A) has been used. Max operating current could be 5 Amp
432
and the compressor has min/max operating pressure of 200/300 psi.
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433 434
Fig. 4 shows the single stage refrigeration unit line diagram of the chamber. Thermostat is used for temperature
435
control. Special precautions are taken to ensure that air going/coming to/from the chamber is not in direct contact of
436
the heating coils.
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439
Two water humidity generators are used for humidification. Electric heater of 2.5 KW is used for heating water for
440
its evaporation inside the chamber. Heating coil inside the chamber is made of copper but it not in contact with the
441
water reservoir storing the water above. Minimum 2 liter of distilled water is needed in the container. Chamber can
442
provide the humidity in the range of 30% to 99.9% with stabilization in the range of ± 3%.Digital Humidity
443
Controller is used which can sense the Relative Humidity (RH) in the range of 0.0 to 99.9% RH. Resolution of
444
sensor is 0.1%RH. If humidity goes above the set value water heater automatically stops.
445
Temperature and humidity sensors are independent to each other. Temperature is controlled by the refrigeration unit.
446
The attached sensor stabilizes of desired temperature under control by sending suitable signals to the refrigeration
447
process, irrespective of humidity or pressure values. Fluctuations are within the range of ± 30C. Similarly humidity
448
sensor stabilizes the chamber humidity generated by the evaporator in the range of ±3%. These are the instrumental
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limitations of present cloud chamber. With high quality of quick response sensors the fluctuation range can be
450
narrowed, in future.
451
3.5 Variability of pressure temperature and humidity.
452
Pressure temperature and humidity are fixed as per the requirement of the experiment. They are designed, in
453
conformity with the actual atmospheric conditions where they keep changing on day to day basis. At any pressure
454
level based on the observed temperature and humidity they both are fixed prior to experiment. They have separate
455
independent controllers. Temperature fluctuation of ±3°C is the maximum limit. It means that if we set the
456
temperature at – 120C then it may slowly vary between -130C to -110C (87%) or at times it may be between -140C to
457
-100C (12%). Rarely (1%) may it go even up to -150C to -90C, but never more than this. Fluctuations are in the
458
interval of 30to 60 seconds. Similar is the case of humidity. Humidity also keeps of varying slowly from its fixed
459
value within the interval of 30 to 60 seconds. In any case mean of the variability taken over any short time interval
460
always remains the desired value. Hence they are not likely to affect the result, significantly. Nevertheless with more
461
advance technology there are scopes of installing more sensitive controllers to narrow the fluctuation range.
462
3.6 Chamber Fan
463
Fans have vertical blades and they rotate around a vertical axis.
464
3.7 Nuclei dispersion Units
465
3.71 Warm Region Dispersion. Fig. 1(b) top right shows the Dry salt powder dispersion container. Notice
466
perforated wall to disperse dry salt by blowing it away by fan.
467
It is located in the upper region of the chamber so that salt particles either remain suspended or gradually fall down
468
by gravity through the humid air. Nebulizer is used for spraying atomized sodium chloride solution droplets. It
469
operates on ultrasonic frequency of 1.7 MHz (±10%) Maximum capacity of small atomizing cup is 150 ml and that
470
of big cup is 350 ml. It atomizes at the rate of 4 ml/min and can continuously work for four hours. Particle sizes
471
range from 0.5 to 5µm. Its water tank capacity is 300ml and power consumption 50VA, Power supply voltage
472
should be 220v; 50Hz.It is located in the upper region of the chamber so that atomized droplets either remain
473
suspended or gradually fall down by gravity through the humid air.
474
3.72 Cold region Dispersion. Fig.1(b) shows the pyrotechnic cartridge burning stand.
475
It is located in the lower region of the chamber so that smoke rises above after getting released from cartridge and
476
fills the chamber. Canopy provides protection to the burning cartridge from any falling rain , drizzle droplet or
477
hydrometeors over it. It also helps spread the fumes.
478
3.8 Electrical and mechanical features and control panel
479
Three phase power of 415V (±10%) and 50 Hz AC supply is needed for the cloud chamber. Its exterior and interior
480
body is made of Satin finish Stainless Steel 304 quality 20 SWG. Chamber is heat insulated by non-inflammable
481
Ceramic/Rockwool of 125 mm thick fiber pad. The pilot light indicators are significant during the operation of the
482
cloud chamber. The meaning of the abbreviations used on the front panel control are explained in table-1 and table-
483
2.
484
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Table-2
485
For hail control we only need to know that how fast and how effectively nuclei induce cloud formation so
487
that Vapor Water Content (VWC) of the cloud is divided in maximum number of small droplets
488
(Sulakvelidze, 1969). Chamber is, therefore, not designed to observe the characteristic of the cloud e.g ice
489
phase or liquid phase or mixed phase. The chamber is also not installed with particle size measurement
490
instrument or size spectrometer (e.g. electrostatic precipitator collection foils for photo micrograph analysis
491
or disdrometer) to know spectrum of cloud particle ensembles. Instead a lux meter serves our objective.
492
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4.0 Making of AgI Pyrotechnic Cartridge for Efficient Ice Nucleation
494
Edwards and Evans(1960) studied the ability of silver iodide particles to act as ice nuclei under controlled conditions
495
of temperature and humidity. They noted that ≈100 Å of effective radius is largely ineffective at ≈ 100% humidity
496
whereas 60 to 75 Å of effective radius are active as freezing nuclei between -8 to -90C and 90 to 100 Å between -6
497
to -70C. Koenig(1964) had noted that AgI particles of several microns in diameter are also not uncommon in
498
pyrotechnic smoke. AgI particles are also photosensitive (Burley and Herrin, 1962) hence different compounds
499
have been attempted to obtain photo resistant suitable particulate size for getting effective nucleation by the
500
burning pyrotechnic cartridge. Ice nucleation by cyclic compounds (Head, 1962) and IN through the combination of
501
AgI-NaI (Mossop and Jayaweera, 1969) had been attempted, since long. DeMott (1982, 1995) had the prime
502
objective to test the efficiency of various compound mixtures in producing maximum IN nuclei for condensation,
503
primarily for the artificial rain making campaigns. He found that mixed AgI – AgCI nuclei display effectiveness
504
values which are one order of magnitude larger at -120C and three orders of magnitude larger at -60C in comparison
505
to the AgI nuclei generated from the AgI'NH4I - acetone - water solution combustion system but he also observed
506
that AgI-AgCl nuclei are relatively slow. For 90% production in 1.5 gm -3cloud it will take 20-30 minutes. Hence,
507
though effective but it cannot become an efficient formulation. Although seeding operation and its efficiency
508
towards cloud formation is significant in all weather modification campaigns, it is extremely important, especially in
509
clouds treated during hail mitigation operations, that seeding agents provide quick and effective nucleation (e.g.,
510
ASCE 2015; Kumar and Pati, 2015; Kumar, 2017).
511
The best pyrotechnic formulation, especially suited for hail control programme, tested in our cloud chamber, is
512
shown in Table – 3. The most suitable formulation was achieved after ten different pyrotechnic cartridges with
513
varying formulation were tested inside the cloud chamber. For details refer Appendix-A.
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Table 3
515
3.0 gm formulation milled to ≤5µm size powder is filled into perforated cylindrical asbestos shell and tightly packed
516
using mechanical press. After all the materials are tightly packed inside an 8mm nicrome wire is inserted inside. The
517
cartridge is then wrapped by transparent tape so as to avoid the contact of moisture with the pyrotechnic
518
formulation. Both the side of the cartridge case is completely sealed by the tape. This cartridge takes less than 15
519
seconds to completely burnout into smoke.
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Reutova et al (1996) analyzed the NH4Cl based pyrotechnic cartridge and noted that during combustion it ingests not
521
only particles of AGI but also HCL and Cl- ions in gaseous phase associated with AgI particles. Gaseous NH3 follow
522
them. The particles of AgI with absorbed layer of Cl- (HCl) and free HCl are able to condense the water vapour
523
owing to strong hygroscopic properties that effect on the cloud processes. Getting into the small cloud droplets or
524
condensing the vapor they are able to create the high concentration of Cl- in ambient water coat. Complex process
525
between Ag, Cl- and NH3 finally leads to increase in solubility of AgI. It was concluded that beside AgI other
526
components also help supports sorption, freezing and sublimation together as observed by Edwards and Evans
527
(1960) in a cloud chamber nucleation process.
528
4.1 Initial conditions of the chamber.
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Initial condition of the chamber with respect to temperature, pressure and humidity has to be fixed as
530
per the requirement of the experiment. For example if pyrotechnic cartridge has to be tested then
531
temperature could be fixed in subzero range of – 40C to – 190C and pressure could be accordingly
532
adjusted based on the actual atmospheric conditions. Humidity could be also fixed varying from 90%
533
to 101%.Similarly if the warm cloud seeding agent e.g. Na Cl or Urea etc are to be tested then
534
chamber initial conditions cloud be fixed anywhere in the range temperature + 100C to 00 C and
535
pressure could be accordingly adjusted based on the actual atmospheric conditions.
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536
Prior to experiment we have also to ensure that the chamber is free from any in situ aerosols. As perfect
538
vacuum is not possible it is important to achieve near vacuum in the cloud chamber for the same. To
539
achieve this chamber is initially brought down to 267 hPa with the help of suction pump. This will help
540
remove any extraneous aerosols to a greater extent, though not completely. Left over aerosols at 267
541
hPa inside the chamber could be negligibly small quantity and may not cause significant error in the
542
lux meter reading. Lux meter reading at this stage shows ≈ 250 Lux. After this step the chamber
543
pressure is brought up to desired level as per the need of the experiment by slowly intake of desired
544
atmospheric air through any one of the three filters of 1µm, 3 µm and 5 µm. If the experiment is to be
545
performed with IN agents of sizes >3 µm or >5 µm or >7 µm then filters of sizes 1 µm or 3 µm or 5 µm
546
respectively are to be used. However from the practical point of view, the smaller is the hole the larger
547
is the experiment set-up time. In all future application it would be the choice of the scientist, based on
548
the demand of the type of experiment, as to what cut off would be desirable. Accordingly filter selection
549
may be made. Once the chamber aerosol sizes are fixed then vacuum sensor guides it to the desired
550
pressure level as per the need of the experiment. Lux meter reading continues to sustain at ≈ 250 Lux.
551
Probability of existence of cloud droplets in the chamber before the experiment begins, is not totally
552
zero because of two reasons. First if the experiment is to be performed with the release of 10µm seeding
553
agent then while bringing the pressure from 267hPa to desired pressure level the inflow into the
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chamber with 5 µm filter would permit aerosols of size ≤ 5µm only. Hence condensation may take
555
place but over lower size aerosols only. Secondly since chamber is not totally evacuated to get 100%
556
vacuum hence some negligibly small number of aerosols might remain inside the chamber to cause
557
condensation. Both the causes would induce small effect only; this had been observed during all the
558
experiments and initial transparency remained close to 250 lux if not exactly 250lux.That is why we
559
maintained that initial lux meter reading would be either ≈ 250 Lux or less. This is as per the luminosity
560
provided by the LED light (250dBZ) source minus the extinction provided by in situ small aerosols(say
561
€ dBZ). During the experiment, therefore, our last regained luminosity should be 250- € dBZ to
562
account for this error.
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563 5.0 Experimental Details
565
Cloud chamber simulates one particular level of atmosphere. Repeated experiments have to be done in the chamber
566
for different levels to get the integrated result for entire cloud.Table-4 presents these results for quasi International
567
Standard Atmosphere. The parameters inside the cloud chamber were set as per the desired requirements. Columns
568
1, 2, 3, 4 of table-4 show the date wise details of observations. Luxmeter readings at 0th min, 5min, 15min and 30
569
min are mentioned in columns 5, 6, 8 and 10 respectively. Column 7 represents the Rate of Nucleation (RN) from 0th
570
min to 5th. As explained in section 2.1 Rate of Precipitation (ROP) is represented by Column 11.
571
represents the transition period when condensation and precipitation both the processes are expected together albeit
572
rate of precipitation apparently dominates rate of condensation during this phase, too.
Column 9 only
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573
Experimental details are presented in appendix – A. It may be inferred that the higher is the difference the faster in the process. The high difference values in columns 7 shows faster spontaneous nucleation process. Similarly higher rate of precipitation could be indicated by the higher values in columns 9 and 11 during the corresponding time periods. To view integrated picture of performance of the cartridge inside cumulus cloud from 522hPa (-4.80) up to 368.7hPa (-200C) layer wise results are stacked up in a tabular form in table 4. Each layer in table 4 is discrete layersample from the continuum structure of cloud atmosphere.
580
The difference of luxmeter readings between 5 min to 0 min, 15 min to 5 min, and 30 min to 15 min were plotted for
581
the standard atmospheric profile for varying temperature in fig 5 and for varying pressure in fig 6.
582
Fig. 5
583
Fig. 6
584
It was just a trial and error method that we discovered that six order fit displays highest coefficient of determination
585
values. For lower order polynomials, the value incessantly decreases. Cause of sinusoidal variation is not clear.
586
Simultaneous variability of pressure and temperature in actual atmospheric conditions as any drop-cartridge is
587
falling from higher level to lower levels may be, possibly, attributed to this sinusoidal behavior. Albeit result have to
588
be further examined with similar experiments in other cloud chambers, too, for cogent acceptance of the argument.
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The trend curve for rate of Nucleation- RNL05 (blue line)is shown on figure 5 and the trend curve of rate of
590
precipitation(RPL10) which predominates over nucleation during the transition period5 to 15 min interval is indicated
591
by violet line (figure 5) . The rate of precipitation (RPL15) between 15 to 30 min intervals is indicated by the green
592
line in this figure. It may be noted that the nucleation process is faster at increasingly lower temperature and
593
precipitation process decreasingly slows down at lower temperature. It has been already verified in past that
594
threshold of AgI seeding activity is near -50C and number of active nuclei increases by order of magnitude for each
595
drop in temperature by 3.5 to 40C down to -150C or -200C (Dennis(1980). Trend line equations for RNL05, RPL10 and
596
RPL15 are shown by the linear regression equations 8, 9 and 10 respectively.
598
RPL10 = 3.1672T + 148.57
599
RPL15 = 2.0029T + 50.119
600
(9)
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RNL05 = -3.0185T + 31.093
(10)
(11)
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Where,
601
RNL(Time interval in min)= Rate of Nucleation in Lux
602
RPL(Time interval in min) = Rate of Precipitation in Lux
603
T= Temperature in 0C
Taking point of intersections of (9) and (10) and that of (9) and (11) we get -190C and – 3.80 C respectively. Hence
605
we may infer that both nucleation and precipitation attain the optimal rate values, between -190C and – 3.80 C.
606
Result is in close conformity with accepted range of optimum results, in actual atmosphere, by AgI – NH4I and AgI
607
– NaI nuclei between – 80C to –160C - former being little more than the later, (Kumar, 2017). With similar colour
608
scheme results could be obtained in the graph plotted against the pressure change in the standard atmosphere. Trend
609
line for rate of nucleation is given by equation (12) which indicates the trend of L2-L1. Rate of precipitation (L3-L2)
610
up to 15 minutes and that up to 30 minutes are shown by the linear regression equation (13) and (14) respectively.
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RPL10 = 0.3482 P - 46.825
612
RPL15 = 0.1985 P - 63.789
613 614
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611
Where,
615
RNL(Time interval in min) = Rate of Nucleation in Lux
616
RPL(Time interval in min) = Rate of Precipitation in Lux
617
P= Pressure mmHg
(12) (13) (14)
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618 Points of intersection of (12) and (13) and (12) and (14) indicate that between 385.86 mmHg and 532.86 mmHg rate
620
of nucleation and precipitation achieved the optimum values together. The mmHg units may be converted assuming
621
International Standard Atmospheric conditions. Similar experiment can be performed by taking any one day’s
622
atmospheric data for pressure and temperature for different layers. Result indicates that in actual atmospheric
623
condition rate nucleation incessantly slows down at lower levels in atmosphere but at higher atmospheric levels it is
624
faster. On the other hand rate of precipitation process is faster at lower levels and incessantly slows down at higher
625
levels in atmosphere. In the present case one may infer that optimum range of pressure where precipitation and
626
nucleation both are optimum is between ≈ 385.86 mmHg and 532.86 mmHg levels. This result is open to
627
verification in future atmospheric seeding experiments.
628
It may be further noted from figures (12) and (13) that rate of nucleation in the standard atmosphere shows a
629
sinusoidal behavior.
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619
Table 5
630 631
Table 5 shows six order polynomial best fit for the rate of nucleation vs temperature (L2-L1) variation in
632
International Standard Atmosphere (ISA). Rate of precipitation vs temperature (L3-L2) after 15 min and 30 min
633
(L4-L3) are also shown in table. Last column shows high degree coefficient of determination. Table 6
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634
Table 6 shows six order polynomial best fit for the rate of nucleation vs pressure (L2-L1) variation in International
636
Standard Atmosphere (ISA). Rate of precipitation vs pressure (L3-L2) after 15 min and 30 min (L4-L3) are also
637
shown in table. Last column shows high degree coefficient of determination.
638
6th order best fit polynomials in tables 5 and 6 for L2-L1 i.e. Rate of Nucleation(RN), are having very high
639
coefficient of determination (≈ 0.9) hence could also be used as statistical prediction model.
640
6.0 Scope of Improvisation
641
Jonathan et al (2007) used Spontaneous Raman scattering and Stimulated Raman spectroscopy for the determination
642
of droplet size with nanometre accuracy and can allow the characterization of near-surface composition. Takahama
643
et al, (2011) had used Fourier transform infrared (FTIR) spectroscopy for organic functional groups (OFG) to
644
separate burning and non-burning forest sources of the measured organic aerosol. Testing of the efficiency of
645
seeding agents, described in the present cloud chamber is currently based on simple optical luxmeter measurements.
646
It is hoped that in future, with the addition of multispectral spectroscopy equipments in the chamber, the scope of
647
researches in this chamber could be multiplied many fold.
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648 649
7.0 Conclusions.
19
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650
i.
This cloud chamber is specifically designed and fabricated to simulate the tropical atmosphere for testing
651
different IN. Optional pressure (<350hPa), temperature ranges (-150 to + 500C) and humidity (30 to 99.9%)
652
have been provided to simulate any particular level’s atmospheric conditions, with in cloud.
653
ii.
In the cloud chamber Pressure could be stabilized at any optional value within acceptable rise margin of 40hPa/hr. Temperature remains stabilized in the range of ± 30C and Humidity sensor keeps it stabilized in
655
the range of ± 3% within 30 to 60 seconds. Humidity can be measured up to 99.9% by digital sensors with
656
resolution of 0.1% RH.
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654
657
iii.
Environment friendly compressors have been used for refrigeration.
658
iv.
Hypothesis of quantitative assessment of cloud formation is based on the assumption that drop in
illumination is directly proportional to particulate concentration per unit volume. Albeit hypothesis
660
is reasonably valid for small size of droplets (≤ 20 µm) it is still uncertain for the solid phase or
661
mixed phase of the droplets e.g. when super cooled liquid droplets and ice crystals are together in
662
the ensemble of nuclei. Fragmentation of a freezing drop in the forms of splintering, shattering, or
663
bursting has been known between the o to -200C (Cheng, 1970; Harris-Hobbs and Cooper, 1987;
664
Yano and Hillip, 2011). Nevertheless further study and experimental verification is needed for
665
applying the exact correction factor (Korolev, et al., 2012).
668
If drop in luminosity is d and total concentration of particulate matters is Cp per unit volume then d
667 vi.
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α
Cp
Rate of Nucleation(RN) is assessed on the hypothesis that Rate of Nucleation (RN)
669
α
L5 - L0
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659
670
Where L0 is the lux meter reading at the time of release of IN and L5 is lux meter reading after 5 minutes of
671
the release of IN.
672
vii.
Circulation fan provided inside the chamber relentlessly keeps circulating the cloud mass with in the chamber, hence cloud particle makes several round of the chamber space during the process of its growth
674
by coalescence or by Bergeron process resulting into growth of cloud droplet . Precipitation could be
675
drizzle, rain or hydrometeor. For Rate of Precipitation (ROP) if the Lux meter reading after 15 Minutes of
676
the release of IN is L15 and after 30 minutes interval if it is L30 then it may be hypothesized that
EP
673
678
viii.
AgI Pyrotechnic cartridge formulation as mentioned in table 3 generates effective cloud seeding nuclei
performed in the standard atmospheric conditions. The results have got to be validated for other
681
combination of temperature and pressure in actual atmosphere.
682 ix.
The rate of nucleation within 5 min of the release of nuclei shows higher values at low temperature (≈ 200C) and slower values at higher temperature (≈ - 50C).
684
686
L30 - L15
and range of pressure between 532.86 and 386.76 mmHg (≈ 710 and 514hPa). Experiments were
680
685
α
which works in the actual atmospheric conditions optimally in the range of temperature -3.70 C and -190C
679
683
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Rate of Precipitation (ROP)
677
x.
The rate of precipitation shows higher values at higher temperature (≈ - 50C) and slower values at lower temperature (≈ - 200C) . 20
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687
xi.
Nuclei. This needs to be reexamined for different size of cloud chamber.
688 689
The process of nucleation and precipitation seems to be complete within 30 minutes after the release Ice
xii.
Six order polynomial successfully simulates the nucleation process for temperature vs luxmeter reading and also pressure vs luxmeter reading. In both these cases it is observed that coefficient of determination
691
shows a very high values. It might be caused due to simultaneous change in temperature and pressure in
692
actual atmosphere.
693 694 695
xiii.
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Six order polynomials in tables 5 and 6 for L2-L1 are having high very coefficient of determination (≈0.9) hence could also be used as statistical prediction model for condensation and rate of condensation.
Acknowledgement.
Author is deeply grateful to Indian Council of Agriculture Research’s programme on National Initiative of
697
climate Resilient Agriculture (NICRA,) for funding this project entitled “Hailstorm Management Strategy
698
in Agriculture”. Author is also grateful to D. Jaykumar,SRF, Debprasad Pati, JRF and Shweta Bhardwaj,
699
JRF, NICRA Project for helping me in various operations/experiments during the fabrication and
700
development phase of cloud chamber. Thanks are due to MIT World Peace University, Pune, Maharashtra,
701
India for providing the new building for the Hailstorm Laboratory. Author also expresses sincere thanks
702
also to both the referee for making valuable suggestions.
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703 References.
705
Am. Soc. Of Civil Eng., (ASCE) 2015, Guidelines for operational hail suppression programs (39-15),
706
Standards ANSI/ASCE/EWRI 39-15, pp 62.
707
Am. Met. Soc.(AMS), 1952, Ed. Ralph E. Huschke, Glossary of Met., Boston, Massachusetts, pp 397-398.
708
TE D
704
Burley G and Herring D.W., 1962, Effect oon Silkver Iodide particles exposed to light, J. of Appl.
710
Meteoro., Vol. 1, 355-356.
711 712 713
Cheng, Roger J., 1970. Water Drop Freezing: Ejection of Micro droplets, Science, New Series, Vol. 170, No. 3965 ,Dec. 25, pp. 1395-1396, American Association for the Advancement of Science. (URL: http://www.jstor.org/stable/1730870).
714 715 716 717 718 719 720 721 722 723 724 725 726 727 728
Chernov,A. A., 1984.Modern Crystallography III-Crystal Growth ~Springer, Berlin.
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709
Colin D. O’Dowd and Waner Paul, 2007, Nucleation and Atmospheric Aerosols, 17th Int. Conf., ICNAA2007, Galway, Ireland, pp-1255. Das Gupta, N.N., Ghosh S.K. 1946.A report on the Wilson cloud chamber and its applications in physics. Reviews of modern physics 18 (2): 225–365.
DeMott J. Paul, 1982. A characterization of mixed silver iodide-silver chloride ice nuclei. Atmospheric science paper no. 349, Department of Atm. Sc., Colorado State University, CO, U.S.A. DeMott J. Paul, 1995, Quantitative descriptions of ice formation mechanisms of silver iodide-type aerosols, Atmospheric Research 38, 63-99
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Dennis A. S. 1980. Weather modification by cloud seeding, Int. Geophysical Ser., Vol. 24, Acad. Press, NY, 1980, pp 107-110.
746 747 748
Harris-Hobbs, R. L., and W. A. Cooper, 1987: Field evidence sup-porting quantitative predictions of secondary ice production rates.J. Atmos. Sci.,44,1071–1082.
749 750
Head, R.B., 1962, Ice nucleation by some cyclic compounds, J. of Phys. And Chem. Of solids, Vol. 23, Issue 10, Oct., pp 1371-1378.
Edwards G.R. and Evans L.F., 1960. Ice Nucleation by Silver Iodide: I. Freezing vs Sublimation, J. Meteo., Vol. 17, 627-634.
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Fukuta N. 1969. Experimental studies on the growth of small Ice crystals, J. Atm. Sc., May, Vol. 26, pp522-531. Garvey. D. M., 1975. Testing of Cloud Seeding Materials at the Cloud Simulation and Aerosol Laboratory, 1971-1973. J. Appl.Meteor.,14, 883-890. Grant and Steele, 1966.Weather Modification by cloud seeding,,Arnett S Dennis. Int. Geophysical Ser., Vol. 24, Acad. Press, NY, 1980, pp 108.
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Hallett, J. and Mossop, S.C., 1974, Production of Secondary Ice Particles during the Riming Process. Nature, 249, 26-28.
751
Jonathan P. Reid , Helena Meresman , Laura Mitchem & Rachel Symes, 2007, Spectroscopic studies of the size and composition of single aerosol droplets, International Reviews in Physical Chemistry, Volume 26, 2007 - Issue 1, Pages 139-192
755 756
Singh H, Datta R K, Chand S, Mishra D, Kannan B,2011. A study of hail storm of 19th April 2010 over Delhi using Doppler weather radar observations, Mausam, Vol 62, Number 3, 433-440.
757 758 759
Summers, P.W., Mather G.K. and Treddenick, D.S., 1972, The development and testing of an airborn Droppable pyrotechnic flare system for seeding Alberta Hailstorms, J. of Appl. Metor., June, Vol.11, 695703.
763 764 765
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Koenig L. Randall,1964, Some chemical and physical properties of silver-iodide smokes, J. Appl. Meteor., Vol.3, 307-310.
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752 753 754
KumarP.,2017. Hailstorm Prediction, Control and Damage Assessment. Second edition, BS Publication and
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CRC Press,Vol. 1, ISBN: 978-81-7800-248-4. pp-286.
767
Kumar P. and Debaprasad, Pati, 2015.Radar Imageries Information Extraction and its use in Pre-Hail
768
Estimation Algorithm, Mausam, 66,4,October,698-712.
769 770 771
Korolev, A., Shashkov A. and Barker H., 2012. , Parameterization of the Extinction Coefficient in Ice and Mixed-Phase Arctic Clouds during the ISDAC Project, Environment Canada, Cloud Physics and Severe Weather Research Section, Toronto, Canada. 22
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Liua X. Y., 2000.Heterogeneous nucleation or homogeneous nucleation? Journal of Chemical Physics, Volume 112, Number 22 8 June..
Liu Guoliang, Manxuan Xiao, Xingxing Zhang, Csilla Gal, Xiangjie Chen, Lin Liu, Song Pan, Jinshun Wu, Llewellyn Tang,Derek Clements-Croome, 2017, A review of air filtration technologies for sustainable and healthy building ventilation, Sustainable Cities and Society 32, 375–396
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Mahen Konwer, Maheshkumar, R.S., Kulkarni J.R., Freud E, Goswami B.N. and Rosenfeld D., 2012, Aerosol control on depth of warm rain in convective clouds, J. of Geophysical Res., Vol. 117, pp-1-10.
Matteo Leoneand Nadia Robotti, 2004. A note on the Wilson cloud chamber (1912), European Journal of Physics, Volume 25, Number 6 , 14 September.
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Mason, B.J., 1957, The physic of clouds, Chs 1-4.
789
McDonald, J.E., 1953, Homogeneous nucleation of supercooled water drops, J.Met., pp. 416-433.
790 791
Mossop, S.C., and Jayaweera, K.O.L.F., 1969, AgI-NaI Aerosols as Ice Nuclie, J. of Appl. Meteo., April, pp-241-244.
792 793
Pruppacher, H.R. and Beard, K.V., 1970, A wind tunnel investigation of the internal circulation and shape of water drops falling at terminal velocity in air, Quart. J. R. Met. SOC. (1970), 96, pp. 247-256.
794 795
Pruppacher, H.R. and Klett James D., 2010. Microphysics of cloud and Precipitation, Atmospheric and Oceanographic Sciences Library, Vol. 18, Spiringer. Ch. 7,pp 191-209 & ch. 9, pp 287-355.
796 797
Reutova, T.V., Zhinzhakova, L.Z., Chernyak, M.M., and Shvedov, S.V., 1996, Nucleation and Atmospheric Aerosols, 14th Int. Conf.,ICNAA-1996, pp-885-888.
798 799
Rogers R. R., and Yuan M.K., 2006, A short course in cloud physics, IIIrd ed., Butterworth-Heinemann Pub.
800
Sohnel O. and Mullin, J. W.1978. J. Cryst. Growth 44, 377.
802 803 804 805
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Skripov, V. P.,1977. In Current Topics in Materials Science, edited by E. Kaldis and H. J. Scheel ~NorthHolland, Amsterdam,. 327–378.
Sulakvelidze G.K., 1969. Rainstorm and Hail, IPST Press, Jerusalam.
806 807 808 809 810
Takahama S., Schwartz, R. E, Russell L. M., Macdonald A. M. Sharma S. and Leaitch W. R., 2011, Organic functional groups in aerosol particles from burning and non-burning forest emissions at a highelevation mountain site, Atmos. Chem. Phys., 11, 6367–6386, www.atmos-chem- phys.net/11/6367/2011/ doi:10.5194/acp-11-6367-2011 23
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Vonnegut, B., 1949. Nucleation of supercooled water clouds by silver iodide smoke. Chem. Rev., 44, 277-
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289.
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Wang P. K. and Pruppacher H. R.1977. Acceleration to terminal velocity of cloud and rain drops, March, Vol. 16, J .of Appl. Met., 275-280.
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Witt A , Eilts M. D., Stump G. J., Johnson J. T., Michell E. D., 1998, An enhanced hail detection algorithm for the WSR-88D, Wea. and Forecasting, 13, 2, 286-303.
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Yano, J.-I. and Hillip, V. T. J. P, 2011, Ice–Ice Collisions: An Ice Multiplication Process in Atmospheric Clouds, Vol. 68,February, pp-322-333
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AMS, U.S.A.2015, Met Glossary: http://glossary.ametsoc.org/wiki/Nucleation
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ANSI/ASCE/EWRI 2015 hail suppression document. http://www.asce.org/templates/publications-book-
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detail.aspx?id=15783
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EPA, U.S.A. 2017 https://www.epa.gov/pm-pollution/particulate-matter-pm-basics#PM
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Towards Design and Development of Isothermal Cloud Chamber for Seeding
2
Experiments in Tropics and Testing of Pyrotechnic Cartridge
3
Tables
4
Table-1 Front Panel Controls
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Description
POWER ON
Light glows when 3 phase mains supply is properly connected in mail sequence.
DOOR OPEN
Light glows when chamber doors are opened or are not properly closed.
O/L CH. FAN
Light glows when Compressor fan is turned off in case of over loading.
O/L COMP 404
Light glows when Compressor R-404 is turned off in case of excessive overloading on
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Pilot Lights
compressor.
Light glows when condenser fan R-404 is turned off in case of over loading
H.P. 404
Light glows when Compressor R-404 is turned off in case of discharge pressure of
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O/L COND. FAN
compressor decreases below the specified limit.
L.P. 404
Light glows when Compressor R-404 is turned off in case of suction pressure of compressor decreases below the specified limit.
Light glows when Vacuum Pump 1 gets turned off in case of excessive overloading on
EP
O/L VACCUM PUMP
VACUUM
Light glows when vacuum is on
DE VACUUM
Light glow when vacuum is being released
OVER TEMP
Light glows when temperature inside the chamber increases beyond the set limit.
LOW WATER
Light glows when water is low in humidifier
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6
7
Vacuum Pump 1.
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8
9
Control Switches of the Cloud Chamber
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Table-2
10
Used to switch on Air Flow
Heat ON/OFF
Used to switch on Heater
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Air ON/OFF
Cool ON/OFF
Used to switch on Cooling
CH. LIGHT ON/OFF
Used to switch on the Chamber light
CH. LIGHT (LUX)
Used to switch on the Luxmeter light
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ON/OFF
POWDER
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DISPERSION
Used to trigger the burning of pyrotecnique cartridge
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AGI ON/OFF
Used to start Powder Dispersion fan
NEBULIZERS
Used to start Nebulizer
HUMIDITY ENABLE
Used to switch on humidifier
VACUUM ENABLE
Used to switch on Vacuum Pump
AUX
Auxiliary Switch
AUX
Auxiliary Switch
EMERGENCY STOP
Used to switch
11
12
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Table 3: AgI Pyrotechnic Cartridge chemical Formulation
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Pyrotechnic cartridges composition Material Percent by Weight Silver iodate 45.0 Potassium perchlorate 27.0 Magnesium 20.0 Nitrocellulose 4.0 Triacetin 4.0 13 14 15 16
20 21 22 23 24 25 26 27 28 29
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Table-4. Results of experiments performed inside the cloud chamber with same formulation of pyrotechnic cartridge as in table-3, at ≈100% humidity and varying temperature and pressure, as per actual atmospheric conditions (vide quasi International Standard Atmosphere). To view integrated picture of performance of the cartridge inside cloud from 522hPa (-4.80) up to 368.7hPa (-200C) layer wise results are stacked up in a tabular form. These layers are the “discrete - samples” from the continuum structure of atmosphere with respect to pressure vis-à-vis temperature.
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Date (dd/mm/yy)
Pressure (mmHg)
Temperature (0C)
Humidity (%)
Lux meter Readings(LUX)
At 0 min L1
At 5th min L2
2
3
4
368.7
-20.40C
99.9%
11.5
112
100.5
214.5
2
10/1/14
376.0
-19.70C
99.9%
55
154
99
201.5
3
15/1/14
395
-18.70C
99.9%
20
104.5
84.5
204.5
4
15/1/14
411.7
-16.50C
99.9%
16
96.5
80.5
207
5
17/1/14
429
-14.70C
99.9%
70
49.5
191
7
23/1/14
446
-12.70C
99.9%
40.5
110
69.5
194
8
24/1/14
464
-10.80C
99.9%
31.5
102
70.5
204.5
9
4/2/14
483
-8.80C
99.9%
14.6
82.2
67.6
211
10
7/2/14
502
-6.80C
99.9%
31
70
39
205
11
11/2/14
522
-4.80C
99.9%
13.7
68.2
54.5
198
33 34 35 36 37 38 39
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Trans ition perio d
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1
20.5
L3-L2
At 15th min L3
10/1/14
31
6
Lux meter Readi ngs(L UX)
1
30
5
L2-L1 (RN)
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Sr.No
9
Lux meter Readi ngs(L UX)
L4-L3 (ROP)
At 30th min L4
10
11
220 102.5
5.5 220
47.5
18.5 212.5
100
8 211.5
110.5
4.5 224
121
33 227.5
84
33.5 229.5
102.5
25 242
128.8
31 236
135
31 241
129.8
43
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Table 5: Polynomial and coefficient of determination of the best fit curve for Temperature vs Luxmeter difference reading Six Degrees Polynomial Equation
L2-L1
y = 0.0009x6 + 0.0704x5 + 2.3005x4 + 38.415x3 + 342.76x2 + 1533.3x + 2713.3
R² = 0.889
L3-L2
y = 0.0017x6 + 0.1237x5 + 3.6122x4 + 53.321x3 + 417.08x2 + 1635.7x + 2645.7
R² = 0.6788
L4-L3
y = -0.0006x6 - 0.0472x5 - 1.4471x4 - 22.424x3 - 183.82x2 749.11x - 1142.5
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48 49 50 51 52 53 54 55 56 57
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coefficient of determination
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Temperature vs Luxmeter difference reading
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R² = 0.8496
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Table 6: Polynomial and coefficient of determination of the best fit curve for Pressure vs Luxmeter difference reading Pressure vs Luxmeter difference reading
Six Degrees Polynomial Equation
L2-L1
y = 9E-10x6 - 2E-06x5 + 0.0025x4 - 1.4163x3 + 455.45x2 77831x + 6E+06
coefficient of determination
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58 59
R² = 0.9302
R² = 0.7171
L3-L2
y = -2E-10x6 + 5E-07x5 - 0.0005x4 + 0.3069x3 - 97.442x2 + 16366x - 1E+06
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y = -5E-10x6 + 1E-06x5 - 0.0014x4 + 0.8285x3 - 273.5x2 + 48109x - 4E+06
60 61
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R² = 0.8454
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Towards Design and Development of Isothermal Cloud Chamber for Seeding
2
Experiments in Tropics and Testing of Pyrotechnic Cartridge
3
Figures Only
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7 8 9 10 11
Fig1a Cloud Chamber – Front door is closed.
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Fig.1(b)Left. Inside view of the cloud chamber. Right-top is the NaCl powder spray unit. It has fan inside for blowing the powder out of mesh. Right-middle is the NaCl nebulizer unit which produces spray of NaCl droplets for seeding. Powder spray unit and the nebulizer unit both are kept on the same platform as per the need of experiment. Right-bottom is the pyrotechnic cartridge burning stand under the canopy. Horizontal pipe holding it has the electric wire for triggering the fire. 15
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20
Air Filters of 1µm, 3 µm and 5 µm
N
Nebulizer
AC C E H HS HPG LED C LMD LR LS
Air Compressor Circulator Fan Evaporator Heater Humidity Sensor High Pressure Valve LED Camera Luxmeter Digital Display Luxmeter receiver Luxmeter Source
OL PTCH PG PRV S Ts VD VS VP
Outlet for Air Pyrotechnic Cartridge Holder Pressure Gauge Pressure Relief Valve Salt powder spry stand Temperature Sensor Video Display Screen Vacuum Sensor Vacuum Pump
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AF
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Fig. 2. Schematic diagram of Cloud Chamber.
3
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25 26 27
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Fig. 3 Extinction correction values1-f, as determined by Monte Carlo simulation (heavy lines)and light lines for water spheres and various pin-hole aperture sizes(as listed on the plot) as functions of particle diameter D. (By Korolev, et al. 2012)
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Fig.4 Single Stage refrigeration Unit line Diagram
29 30
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Temperature Chart 160 140
100 80 60 40 20 0 -25
-20
-15
38 39 40
47
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0
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-5
Figure 5: Graph showing best fit six order polynomial curve and trend line for Temperature (0C) at x-axis vs Lux meter reading difference at y-axis (L2-L1 in blue, L3-L2 in red, and L4-L3 in green)
41
43
-10
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Pressure Chart 160 140
100 80 60 40 20 0 550
500
450
49 50 51
53
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300
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Figure 6: Graph showing best fit six order polynomial curve and trend line for Pressure(mmHg) at x-axis vs Lux meter reading difference on y-axis (L2-L1 in blue, L3-L2 in red, and L4-L3 in green). At 00C, 0.0075006156130264 mmHg = 0.01 hPa.
52
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Figure A1 Perforated pyrotechnic cartridge. Case made up of PVC
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300
250
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200 0 min
150
5 min 15 min
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30 min
0 PC11
PC10
PC9
PC8
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PC6
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PC3
PC2
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Figure-A2: Graph showing Nucleation and growth to precipitation by different pyrotechnic cartridge at 0 min, 5min, 15 min, and 30 min. All cartridge testing experiments were conducted at 98% RH and temperature -100C. Each cartridge got completely burnt after the nicrome trigger within 20-30 seconds. Graph show that the cloud takes about 30 minutes to come into a quasi-steady state equilibrium, and that as the number of nuclei continue to be ingested they coagulate. In some cases because of the method of their creation and resulting coating act as submersion nuclei, allowing cloud – aerosol interaction that yields a broadening of the droplet size distribution.
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Highlights 1.
A new Isothermal cloud Chamber is designed and fabricated based on optical scattering concept. It is first of its kind for testing the efficiency of seeding agents in simulated warm or cold cloud condition. Results obtained for optimum temperature range of efficiency for IN seeding; match fairly well, with
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preexisting results independently obtained after actual atmospheric seeding. 3.
Entire process of condensation growth and precipitation takes place only ≈ 30 minutes within the chamber.
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6th order polynomial successfully simulates the spontaneous condensation process for simultaneous
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Percentage Cartridge efficiency has been defined
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variation of pressure and temperature with very high coefficient of determination.
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S1364-6826(18)30133-0
DOI:
10.1016/j.jastp.2018.10.002
Reference:
ATP 4927
To appear in:
Journal of Atmospheric and Solar-Terrestrial Physics
Received Date: 22 February 2018 Revised Date:
30 September 2018
Accepted Date: 3 October 2018
Please cite this article as: Kumar, P., Towards design and development of isothermal cloud chamber for seeding experiments in tropics and testing of pyrotechnic cartridge, Journal of Atmospheric and SolarTerrestrial Physics (2018), doi: https://doi.org/10.1016/j.jastp.2018.10.002. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Towards Design and Development of Isothermal Cloud Chamber for Seeding Experiments in Tropics and
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Testing of Pyrotechnic Cartridge
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By
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P.Kumar,
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(NICRA Project, ICAR, Ministry of Agriculture, Govt. of India)
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Department of Mathematics, MIT-World Peace University, Pune.
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Email: [email protected],Phone: +919860705053
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Abstract
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Isothermal cloud chamber with capacity of 120x120x120 cm3 has been designed and developed for performing
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cloud seeding experiments in simulated tropical atmosphere. Purpose of the chamber is to test the efficiency of
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artificially generated IN (for cold region of the cloud) or CCN (for warm region of the cloud) agents, in simulated
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pressure, temperature or humidity condition as in natural cloud layers (levels). Level to level results can be
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subsequently tabulated together in sequence to view an integrated picture of the performance of the existing agent
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formulation in entire(simulated) natural cloud condition.
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Chamber pressure is designed to achieve up to 350 hPa and lower temperature is designed to get -250C. Controlled
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higher temperature in the cloud chamber is designed to reach ≥ +100C (even up to +500C). Humidity could be
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controlled in the range of 30% to 100 %. This isothermal chamber is designed primarily to test the seeding
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efficiency.
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Hypotheses used are;
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If the Lux meter reading at the time of release of IN is L0 and after 5 minutes# if it improves to L5 then
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If drop in luminosity is d and total concentration of particulate matters is Cp per unit volume then
If the Lux meter reading after 15 minutes# of the release of IN is L15 and after 30 minutes# interval if it improves to L30then
Rate of Nucleation (RN)*
α
Cp
(1)
α
L5 - L0
(2)
α
L30 - L15
(3)
(*It includes condensation and Ice nucleation both)
Rate of Precipitation (ROP)
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(# Broad chronological classification)
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The hypotheses are reasonably valid for small size of droplets (≤ 20 µm). For the solid phase or mixed phase of the
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droplets further examination is needed to apply correction factor. Loss of moisture due to deposition on wall is
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incessantly replenished by the humidity controller to simulate nature. Incessant growth in the luminosity-drop only
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indicated the active process of nucleation and subsequent growth in size of particles. The faster the process the
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higher is the efficiency of the seeding agent.
27 It was found that the optimal range of atmospheric temperature and pressure for effective cold region seeding is -
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3.70C to -190C. Entire process of condensation growth and precipitation takes place only ≈ 30 minutes within the
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chamber.
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6th order polynomial successfully simulates the spontaneous condensation process for simultaneous variation of
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pressure and temperature with very high coefficient of determination.
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Keywords. Cloud Chamber, Rate of Condensation, Rate of Precipitation, Quantitative measurements of aerosols,
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lux meter
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1.0 Introduction
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Various types of cloud chambers have been developed as apparatus for different types of experiments in several
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disciplines of science and engineering. Wilson’s original cloud chamber, initially developed in 1912, was a glass
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cylinder, about 16 cm across and about 3 cm deep. Its walls were coated in gelatin, with the base dyed black for a
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photographic dark background. The floor of the chamber was fixed to the top of a brass plunger. It all stood in a
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shallow trough of water that kept air in the chamber saturated with water. A diaphragm was used to expand the air in
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the chamber for adiabatic expansion, cooling the air and starting to condense water vapor. This kind of chamber is
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called a pulsed chamber because the conditions for operation are not continuously maintained. Wilson Cloud
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Chamber which provided adiabatic expansion (Das Gupta and Ghosh -1946;Matteo and Nadia , 2004) became a
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fundamental tool of research not only in atmospheric science but also in nuclear, cosmic ray and elementary particle
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physics. The close examination of the expansion apparatus, the illumination method and the photographic method
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showed that the cloud chamber is a fine example of experimental ingenuity. Cloud Chambers for weather studies
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have been described by Grant and Steele (1966), and Garvey (1975). Colorado State University(CSU) modified
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Garvey’s chamber known as CSU Isothermal Cloud Chamber (ICC). Advance features e.g. Particle Measurement
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Systems, dew-point and airflow calibration installation of an acoustic sensing ice crystal counting device were
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introduced in ICC(DeMott,1982).
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Cloud Chambers are used for various types of testing e,g, prototype evaluation, reliability testing, failure analysis
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and many other application where environmental simulation is needed. Cloud Chambers are aimed to simulate
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virtually any type of environmental condition such as temperature, humidity, altitude, solar, wind & rain, dust, etc.
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Various sizes of cloud chambers are available ranging from small bench-top chambers to large living room size
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chambers for cloud seeding experiment purpose. They provide temperatures range from -40°C to +50°C wherein the
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optional humidity could be controlled from 10% to 95% and different pressures to simulate atmospheric conditions.
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There are various kinds of cloud condensation nuclei/Ice nuclei chambers for performing experiments with different
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cloud seeding agents (Kumar 2017). With an objective to help seeding campaigns, in the present paper an attempt
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has been made to design and develop a simpler and cheaper isothermal cloud chamber for testing the efficiency of
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any pyrotechnic cartridge - releasing IN agents in cold cloud regime - or that of any CCN agents in warm cloud
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regime. Later could be released either by dispersion of finely ground particles or sprayed through atomizer as
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droplets, from a brine solution.
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1.1 Some definitions in context of atmosphere.
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Particulate matter: Particulate matter is the term used for all solid particles suspended in air. Aerodynamic size (effective diameter de) of a particle of less than 10 µm, 5 µm and 2.5 µm are known as PM10 PM05 and PM2.5 respectively. EPA, U.S.A.2017 b) Nucleation: Any process by which the phase change of a substance to a more condensed state (condensation, sublimation, freezing) is initiated at certain loci within the less condensed state. AMS, 1952; McDonald, 1953; Mason, 1957. c) Heterogeneous nucleation: Nucleation loci are particles which exist in different, almost invariably more condensed initial state than the condensing or freezing matter. The particle may be of the same substance as that which is changing state. AMS, 1952; McDonald, 1953; Mason, 1957.
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d) Homogeneous nucleation: It occurs when the change of state centers upon loci which exist in the same initial state as the changing substance. In this case the nucleation system contains only one component and it is termed as spontaneous nucleation. AMS, 1952; McDonald, 1953; Mason, 1957. Reaction Time: Time duration taken by the cumulus cloud to turn into hailstorm (Kumar and Pati, 2015; Kumar, 2017). Total Reaction Time (TRT) is defined as the time taken by any growing cumulus cloud from reflectivity of 20 dBZ to 45dBZ. Available Reaction Time (ART) is the time actually available within the TRT for seeding campaign for Hail mitigation.
At low super saturations, heterogeneous nucleation will be dominant, and at high super saturations, homogeneous nucleation will occur (Chemov, 1984; Skripov, 1977; Sohnel, 1978;Colin and Wagner, 2007; Pruppacher and Klett, 2010).
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1.2 Need for efficient seeding agent and optimum Temperature and Pressure regime. A seeding agent which is quick and effective is an efficient seeding agent. Garvey(1975)had defined effectiveveness as number of ice nuclei active at a given temperature per gram of nucleant burned and is determined in the manner similar to that described by Vonnegut(1949). Quickness is needed due to limitation of reaction time and effectiveness demands suitable environmental conditions for the seeding chemicals for optimum results e.g. suitable environmental temperature and pressure. While time limitation is a constraint in several weather modification activities e.g. rain increase, fog dispersal etc., it has high significance during hail mitigation campaigns due to the limitation of Reaction Time (refer 1.1g). Reaction time could be less than 90 minutes. Hail mitigation measures need massive seeding of cloud before hail has formed (Kumar, 2017). Also if the seeding nuclei are not delivered in the suitable temperature and pressure range results could be unsatisfactory. Effectiveness of seeding agent is the number of ice nuclei active at a given temperature per gram of nucleant burned (Vonnegut, 1949). During Alberta hail project Summers et al, 1972 had noted strong temperature dependence of effective nuclei per gram of AgI burning. Number of effective nuclei at -50C were 8x1010 whereas it rapidly rose to 4x1015 at -200C. Superior performance near -50C of acetone generators contained with AgI-NH4I solution is generally recognized in laboratory and field experiments(Dennis, 1980). Hence quick transportation and delivery of seeding agents and their quick response after they are ingested into cloud to produce precipitation, is most important in hail mitigation (ASCE, 2015). This chamber is, therefore, designed not only to test the effectiveness of the CCN or IN agents under different environmental conditions but also to develop the efficient pyrotechnic cartridge (cold cloud seeding) which is capable of producing smoke in shortest possible time. For cold cloud seeding experiments, desired subzero cloud environment may be simulated in the chamber. Fig. 1(a)
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Fig. 1(b)
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Similarly warm region of the cloud can also be simulated in the chamber by fixing its temperature and pressure
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equivalent to any level of warm region of the cloud, along with ≈ 100% humidity. Thus warm cloud seeding agents
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e.g. NaCl dust dispersion or brine solution atomizer, may be tested in the chamber.
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In the present paper design and full size fabrication (refer fig. 1) of a cloud chamber is presented for performing
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various experiments of cloud seeding with different chemicals. In tropics as the base pressure level of the cloud
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could be 900 hPa or more and cloud top could be 200-150 hPa or less, the cold seeding or warm seeding could be
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planned separately as per the actual atmospheric level. For achieving near vacuum state within chamber the pressure
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can be brought down up to 267 hPa. Lower temperature could be controlled up to -250C. 0
0
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Further as base
temperature of the cloud in tropics could be ≈ +10 C or more (± 3 C) hence controlled higher temperature in the
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cloud chamber is designed to reach ≥ +100C . Humidity could be controlled in the range of 30% to 100 %( ± 3%).
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Arrangements are made to introduce pyrotechnic cartridges system which will burn and generate plumes of silver
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iodide for the cloud seeding purpose. There is also arrangement to introduce the finely ground (effective diameter ≈
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< 5µ), warm cloud CCN agents (e.g. NaCl, CaCl) dust particle as well as there is one nebulizer provided to spray
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solution droplets (< 5µ), with in the chamber. The chamber is also attached with steam generation unit (electrical
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heating system) so as to maintain controlled humidity (RH) at any level between 30% up to 100%.Special care has
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been taken so that electrode surfaces are perfectly sealed and are not exposed into chamber to ensure no charge
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transfer into steam or chamber atmosphere.
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The chamber has been designed with objective to test the efficiency of seeding chemicals in warm or cold cloud
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conditions. It assesses the degree of opacity of the cloud through lux meter and unlike chamber by DeMott(1982) no
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particle counters or particle size measurement instruments are separately installed. Lux meter is relatively much
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cheaper equipment than expensive particle counter. With 1 µm pinhole diameter the (extinction correlation value is
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≈ 1; Korolev, et al., 2012) the aberration due to size variability is negligible (explained in section 2.1). Lux meter
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(accuracy ±1 Lux) is installed inside the chamber to qualitatively sense cloud formation in the chamber and its
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subsequent disappearance, as cloud droplets gradually transform into drizzle, rain or hydrometeor and fall on the
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chamber floor. The lux (symbol: lx) is the SI derived unit of luminance and luminous emittance, measuring
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luminous flux per unit area. It is equal to one lumen per square meter. In photometry, this is used as a measure of the
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intensity, as perceived by the human eye, of light that hits or passes through a surface. Chamber is equipped with
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LED light source to help camera to spontaneously display chamber occurrences on the computer digital screen
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outside.
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Theoretical principle of cloud chamber is described in section 2. Descriptions of various hardware are presented in
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section 3. Method of making a pyrotechnic cartridge with specific formulation has been described in section 4.
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Experimental details of testing of pyrotechnic cartridge in the cloud chamber and analysis of results are presented in
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section 5. Section 6 concludes the paper. Appendix-A describes the testing of 10 different cartridges with slightly
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varying formulation which were tested in the cloud chamber. Lux meter readings, for all ten cartridges in Appendix-
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A, at 0, 5, 10, 15 and 30 min intervals, were taken. The formulation which indicated quickest nucleation and
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quickest precipitation was selected as best formulation of cartridge for experiments.
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2.0 Principle of Assessment of Cloud and Precipitation within cloud Chamber
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Refer schematic line diagram in fig. 2. Fig.2
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Lux meter is installed in the cloud chamber with its pinhole source of light (LS) on the inside left panel of the
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chamber wall and its receiver (LR), is installed on the inside right panel of the chamber wall, directly opposite to
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source of light. Beam from LS travels across the chamber’s width (120cm) and reaches the receiver LR. Illumination
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received at LR is digitally displayed on the screen (VD) fixed outside the chamber. The lux meter is calibrated in
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such a way that when there is no interference or obstruction for the beam then it displays 250 lx (250 Lux (lx) =
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371.6 Candela (cd) for 120 cm distance). If there are beam obstructions by particulate matters or liquid droplets and
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if the received illumination at LR is LRC then the drop (d) in illumination from 250 lx is given by d = 250 – LRC. If
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total concentration of total nuclei, cloud and precipitation hydrometeors between Ls and LR is Cp per unit volume
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then we can assume that
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d
α
N(Number of condensed, frozen or mixed nuclei or embryos between LS and LR)
α
s (Cross section area of each particulate matter between Ls and LR)
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Equation (1) may be combined as
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d
α
KNs
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(1)
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(1.1)
Where K is the chamber-constant for the specific cloud chamber and equals to Q (I0/S0) where Q is the total photo
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extinction efficiency of nuclei plus photo extinction efficiency of supercooled and non supercooled droplets, I0is
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incident light intensity and S0 is the uniform cross section of the cylindrical beam from LS to LR.
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Cp therefore is defined as the net water mass per unit volume in liquid phase or solid phase or mixed phase between
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LS and LR (Korolev, et al., 2012).
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Hence for the cloud chamber we can hypothesis that
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d
Cp
(1.2)
The hypothesis can be explained by the Beer-Bouguer law as
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I = I0 e - β(ʎ) L
(2)
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Where I0 is incident light intensity I is light intensity transmitted through the medium in the forward direction (i.e.,
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parallel to the incident light),β(ʎ) is volumetric extinction coefficient at wavelength ʎ, and L is geometric distance
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between emitter and receiver which is 120 cm for this cloud chamber. If we consider the Beer-Bouguer law in the
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differential form for a medium consisting of mono disperse particles with the concentration n and thickness dx, 5
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dΙ = σnΙ0 dx
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(3)
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scattering cross-section of one particle; s is the geometric cross-section of the particle; and Q is the extinction
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efficiency. The particle concentration n can be presented as n = dN/dV = dN/(S0 dx) where dN is the particles in
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volume dV and S0 is the cross section of the beam from LS to LR
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Then
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Left hand side of eqn. 4 is the drop in intensity after the light beam traverses a distance dx. Combining eqn.4 with 3
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and integrating for spatial rate of change of dN from x= 0 to x= L (=120 cm) we get
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LRC - Ls
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Q and s are variable but for small particles (≤ 20µm) the extinction efficiency (Q) may be assumed to be constant for
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pinhole source of light. It is discussed in section 2.1, in detail. When chamber is not having any super cooled cloud
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droplet or ice crystal its luminosity is indicated as ≈ 250 Lux (explained in later part of this section and in
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Appendix-A).It is pointed out that display of 250 lx prior to experiment is due to aggregate of LED in the chamber
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and in situ ambient atmospheric aerosols, rudimentarily left inside, despite the lowest pressure achieved after the
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suction. Once the cartridge is burnt it releases several nucleating agents. Those which nucleate will grow and fall
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down but at the end smoke particles, generated due to burning of cartridge casing may not nucleate and will still
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remain suspended. They would continue small degree of interference(due to smaller size) and hence after each
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experiment the luminosity would not revert back to exactly 250 but would be little less than 250 Lux(LS<250). But
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the drop in luminosity will be caused by those particles which have nucleated and fell down. We are concerned with
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nucleated particles not those which do not participate in nucleation; Hence we can have
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250 – LRC (Since LS≈ 250 Lux) d
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The higher the drop in illumination on LR from its highest value (≈ 250 Lux), the higher is the concentration of
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liquid droplets or solid aerosols or cloud /precipitation droplets, in the cloud chamber, filling the space between the
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source (LS) and the receiver (LR) of Luxmeter. Therefore formation of cloud/precipitation could be directly related
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to drop (d) in illumination from 250 Lx.
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Ls transmission is through circular pinhole of diameter is 1µm. Ab-initio reading of ≈ 250 lux meter prior to release
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of any IN is net luminosity which is the sum total LED and in-situ aerosols as permitted by the filter, prior to the
Qs (dN/(S0 dx)) I0 dx
α
Qs dN I0/S0
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experiment. Once ensemble of INs are released the super cooled droplets or ice crystals will have size not less than
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size of IN. Hence 1µm is the lower limit for all the subsequent droplets or ice crystals during the progress of
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experiment. As per the manufacturers specification the Lux meter installed in the cloud chamber can operate for a
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wide range of luminosity varying from 0 to 2000 lux with the least count accuracy of 1 lux but chamber has one
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LED source installed for visualizing the chamber operations on a display screen of computer kept outside the
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chamber. Hence cloud chamber is never totally dark. When chamber is not having any cloud particles its luminosity
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is indicated as ≈ 250 Lux. This is as per the illumination of the chamber provided by the LED light source and is
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totally independent of temperature, pressure and humidity. Also when the chamber is full of cloud droplets, the
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lowest lux meter reading at very low temperature and pressure, during best seeding results, showed ≈10 Lux. Both
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these values are cloud chamber specifications. Hence the instrumental operational limits of the lux meter in the
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cloud chamber ranges from 10 to 250 Lux. For each gram of seeding substance in the pyrotechnic cartridge the
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resulting smoke may generate IN in the range of 1010 to 1016 nuclei. Nevertheless the count depends on temperature
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pressure and humidity of chamber. This estimate is based on the chamber particle counters from De Mott (1982). On
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an average it could be 1014(Rogers and Yuan, 2006). It can vary based on the design of the chamber(Edwards and
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Evans,1960).
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Improvement in the Lux meter reading is independent of the type of process of rain formation, i.e. may it be
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Precipitation process by Wegener - Bergeron - Findeisen process or ice crystal process and/or by collision –
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coalescence (Mahen et al 2012) or may it be both the processes together followed by Rain or drizzle droplets could
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get deposited either on chamber side walls or fall on chamber ground or remain suspended anywhere within the
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empty chamber space.
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2.1 Does particle size influence the Lux meter reading?
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In general it is known that forward scattering by particles is likely to introduce errors in the observed ‘LRC ’ value in
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eqn.5. Mie scattering calculations show that forward scattering is relatively weak for small particles (de< 10 µm; de
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is effective diameter), and so in the case of small droplets. Unlike natural conditions in a laboratory cloud chamber
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due to limited freedom of movement within limited space, the cloud particles are unable to grow to large natural
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drizzle or rain size, although they still precipitate and fall as relatively much smaller droplets. Fukuta (1969) had
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measured the size of fog droplets after artificial seeding in a cloud chamber. All the droplets were less than 20 µm
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in diameter and out of them mostly (≈ 80%) were less than 10µm in diameter. Hence particles (de< 10 µm) will
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not cause any significant error albeit some error is likely by larger droplets (>20µm).This needs to be further
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examined.
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Reliability of equation 1.2 is inherent in the correct value of ‘d’ which is guided by LRC value. Korolev, et al.,
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(2012) had noted that any possible aberration in the value of LRC would depend on the stability of volumetric
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extinction coefficient (β(ʎ)) at wavelength ʎ. β(ʎ) depends on size and phase of the particle. They had shown that
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β(ʎ) = β0(1 – f) where β0 is the absolute extinction coefficient without any forward scattering. Parameter f (0≤ f ≤1)
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characterizes the forward scattering due to variation of size. Results of Korolev, et al., (2012) are shown in Fig. 3. It
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shows th e e xtinction correction values ‘1-f’,as determined by Monte Carlo simulation (heavy lines)and by
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Korolev, et al., (2012) in light lines, for water spheres and various pin-hole aperture sizes(as listed on the plot)as
247
functions of particle diameter D. It is known through wind tunnel studies that a droplet of diameter smaller than
248
140 µm had, within the experimental error no detectable deformation from spherical shape, Pruppacher and
249
Beard, 1970. The smaller is the diameter (lesser than 140 µm) the more is the spherical shape of the droplet.
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Fig. 3
It is observed that for small size droplets (≤ 20µm) the extinction correlation value is ≈ 1 for pinhole size beam
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diameters as shown on the fig. 3. The smaller is the hole the better is the stability of extinction coefficient.
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Korolev, et al., (2012) results are valid for liquid droplets but uncertainty prevails for the solid phase or mixed
256
phase of the droplets. Further study and experimental verification is needed for applying the exact correction
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factor
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2.2 Selection of time of observation for Rate of Condensation and Rate of Precipitation.
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Jonathan et al (2007) had noted that optical spectroscopy can provide a strategy for the direct assessment of particle size, composition and phase. Spontaneous Raman scattering can allow the unambiguous identification of chemical components and the determination of droplet composition. Stimulated Raman spectroscopy can allow the determination of droplet size with nanometre accuracy and can allow the characterization of near-surface composition. When combined, the mixing state and homogeneity in droplet composition can be investigated. The drop in luminosity(d) is the result of scattering from the condensed, frozen or mixed nuclei or embryos between LS and LR hence it may be possible to extract an estimate of the 'chemical signature' related to the seeding. With the back-up of its chemical signatures it may be stated that the lower the initial Lux meter reading the higher is the efficiency of IN of specific composition. Fukuta (1969) had also observed that within 12 seconds after seeding in the cloud chamber the fall velocity of all the hydrometeors were more or less same regardless of the temperature of super cooled fog. This is the period before marked growth habit differences start to appear. As they grow in size their fall velocity will depend on their size, phase and the temperature inside the chamber. Equation of motion (Wang and Pruppacher, 1977) of water drop of mass m is
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(6)
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Where V is the instantaneous velocity of the drop, t time, a the radius of the drop, ρw the density of water, η and ρ
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are the dynamic viscosity and density of air, respectively, FD is the drag force on the drop, g is the acceleration due
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to gravity, CD = 2 FD / πa2ρV2is the drag force coefficient of drop and NRe = 2aρV/η is the Reynolds number of the
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drop. The equation has to be solved numerically for CD and NRe are functions of V. But for small drops falling in the
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Stokes regime CDNRe/24 = 1 hence integration of resulting linear equation gives,
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(7)
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Where VT is the drop’s terminal velocity. Thus viscous relaxation time τs for spherical drop falling in Stokes regime
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is
(8)
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As temperature decreases from -50C to -200C the relaxation time increases from 1.299x103a2 to 1,361x103a2. Where
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m is mass of the droplet, a is radius of drop in cm, ρw is density of water. It is very small time interval for a droplet
284
to reach its terminal velocity. Fukuta(1969) observed that between the temperature range of -50C to -200C, after 45 –
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50 seconds of growth the terminal velocity of falling particles in cloud chamber were 2 to 4 cm/sec. Broadly with
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this fall velocity itself any particle will take about 30 sec to 1minutes to travel a distance of 120 cm(inner height of
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chamber) under calm wind conditions. But due to continuous stirring of the cloud volume inside the chamber a
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broad cut-off time of 5 min was adopted during the experiment as condensation dominant period. Though it is
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practically impossible to determine as to when condensation slowed down to insignificant level (after complete
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burning of cartridge) and when pure droplet-growth by coalescence or Bergeron process and subsequently by Hallet-
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Mossop process (temperature range -30C to -80 C) took over (Hallet and Mossop, 1974). In fact all these process
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(e.g. nucleation and growth) may be expected to carry on after 5 min too, albeit nucleation rate will slow and its
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magnitude is expected to be significantly less whereas growth of droplets are certainly expected to sustain. Bergeron
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process or coalescence process or both types of precipitation formation are expected to remain functional during the
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entire period till d ≈ 0. As the cloud droplets are regularly growing in the chamber, hence any period during the
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improvement phase of Lux meter reading could be selected to determine the rate of precipitation. However to ensure
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that the process of precipitation strongly dominated the nucleation process on safer side one could take second half
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of the total period of improvement (back to ≈ 250 Lux) for the assessment of rate of precipitation. It could be
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assumed that by that time most of the CCN/IN released in the cloud chamber got converted into cloud droplets. We
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may call the time interval after 15 minutes as the precipitation phase.
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Hence we named ≤ 5 min as the nucleation phase (Phase –I), 5 – 15 minutes as the transition or mixed phase (Phase-
302
II) and 15 – 30 minutes as the precipitation phase (Phase-III). This is a broad classification for the present chamber
303
volume as temporally the processes would depend on the composition of the nuclei introduced into the system, the
304
chemistry of the system, and the meteorology of the system, and the effect of the release of latent energy resulting
305
from the ingested seed nuclei.
306
2.3 Hypotheses of Rate of Nucleation and Rate of Precipitation
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Process of nucleation begins spontaneously (within ≈ 10 milliseconds; Kumar 2017) after release of AgI IN (Icing
308
Nuclei). Precipitation process by Wegener - Bergeron - Findeisen process or ice crystal process and/ or by collision
309
–coalescence (Mahen et al 2012) for cold cloud is also expected to begin immediately after the cloud formation
310
within the chamber vis-à-vis improvement in the Lux meter reading. As the process of nucleation has to precede the
311
rain formation short interval following release of AgI IN could be identified to determine the spontaneous Rate of
312
Nucleation (RN) during which process of condensation, freezing and sublimation dominated the process of
313
precipitation. During all the experiments inside this chamber-volume it was observed that from the time of release of
314
IN the ‘d’ value tends to reach zero within about 30 minutes; may it be warm cloud/cold cloud environment.
315
Influence of chamber design over the apparent activity of silver–iodide in cold chamber was also noted by Edwards
316
and Evans (1960). IN particle results by different formulations of pyrotechnic cartridges are shown in Appendix-A.
317
Reversal of luminosity back to ≈ 250 level after the completion of experiment is the testimony that all the released
318
nuclei nucleated, grew in size and fell down by gravity. Abundant supply of moisture and limited period of
319
nucleation is the reason for it.
320
Warm cloud seeding devices are shown in fig.1(a)(b) in the upper part of the chamber. Natural environment with
321
respect to pressure, temperature and humidity (≈100%) of any desired warm levels between LCL to 00C of the cloud
322
can be simulated in the chamber and efficiency of CCN agents may be tested. During Cloud Aerosol Interaction and
323
Precipitation Enhancement Experiment(CAIPEEX) in India Mahen et al, 2012, found that in monsoon clouds over
324
indo-Gangetic plains the precipitation were initiated as super cooled raindrops at a temperature of – 80C. To
325
experimentally ascertain if the combined seeding of IN and CCN might have any adding affect over condensation
326
and precipitation process, lower levels in cold region may be simulated in the chamber and simultaneous or separate
327
seeding by pyrotechnic cartridge and NaCl dust or atomized solution may be conducted in laboratory.
328
In the isothermal chamber under the near saturation or super saturation of humidity at any temperature cloud
329
condensation or ice nucleation would take place spontaneously after the release of the IN. This initial condensation
330
or ice nucleation can be defined as spontaneous Nucleation. Spontaneous nucleation divided by duration of time is
331
defined as spontaneous Rate of Nucleation (RN). As initial 5 minutes after the release of IN could be assumed to be
332
dominated by the nucleation process hence if the Lux meter reading at the time of release of IN is L0 and after five
333
minutes interval if it is L5 then it may be hypothesized that
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Rate of Nucleation (RN)
α
L5- L0.
(9)
335
Validity of eq. (9) for cloud chamber is explained in sec. 2.1 and 2.2. Eq. (9) can extract the efficiency of chemical
336
signature of any IN agent. The higher the value of Rate of Nucleation, the higher is the effectiveness of IN released
337
in the chamber in rapidly producing ice crystals from water vapour.
338
If the Lux meter reading after 15 Minutes of the release of CCN’s is L15 and after 30 minutes interval if it is L30 then
339
it may be hypothesized that
340
Rate of Precipitation (ROP)
α
L30- L15
(10)
341
Eq. (10) can give the assessment of rate of the precipitation process within the chamber to a reasonable accuracy.
342
The higher the ROP the faster is the process of precipitation. Advantages of the assessment schemes hypotheses 10
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343
mentioned in eq.s(1), (9) and (10) are that they are independent of the profile of change in luminosity with respect to
344
time, may it be linear or non-linear and also it doesn’t require expensive particle counter equipment. Luxmeter is
345
much more economical.
346
Based on the hypotheses (1), (9) and (10), in the present chamber volume, RN and ROP can be defined as, below; (i)
and that at 5 minute (L5) as = kc (L0 – L5) gm/sec; where kc is proportionality constant (gm/Lux. sec).
348 349
Rate of Nucleation (RN): It is defined with difference between the Lux meter reading at 0 minute (L0)
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(ii)
Rate of Precipitation (ROP): It is defined as kp (Lt – Lt’) gm/sec; where kp is proportionality constant
350
(gm/Lux. sec). t and t’ in phase –II are 5 minutes and 15 minutes and in phase – III 15 minutes and 30
351
minutes respectively.
It may be noted that above hypotheses are specific for the volume of present cloud chamber - having capacity of
353
120x120x120cm3. Author feels that independent examination of corresponding hypotheses with different ‘chamber
354
size’ and ‘time frame’ might show path of miniaturization of atmospheric processes in space and time.
355
3.0 Description of cloud chamber
356
Fig1(a), Fig1(b) show the outer and inner view of cloud chamber. Fig1(a) is the look of cloud chamber when the
357
door is closed.In Fig.1(b)-Left the inside view of the cloud chamber is shown. Right-top is the NaCl powder
358
dispersion unit. It has fan inside for blowing the powder out of mesh (several hole of diameter = 1.0 cm) into the
359
chamber. Right-middle is the NaCl nebulizer unit which produces spray of NaCl droplets for seeding. Powder
360
dispersion unit and the nebulizer unit both are kept on the same platform as per the need of experiment. Right-
361
bottom is the pyrotechnic cartridge burning stand under the canopy. Horizontal pipe holding it has the electric wire
362
for triggering the fire through the nicrome wires connected to cartridge. Electrical wiring in the pipe is thoroughly
363
insulated to ensure no charge transfer to pipe casing. Small nicrome wire in the cartridge produces momentary
364
spark to trigger the burning then switches off the electrical current. During rest of the period the cartridge burns
365
by itself. This scheme ensures that there is no charge transfer to chamber aerosols. Schematic line diagram of the
366
cloud chamber (fig.2) gives the overview of the locations of Pressure Controller (Vacuum Pump-VP), Temperature
367
Controller (Refrigeration system- e.g. Air Compressor (AC) and other systems) and Humidity Controller
368
(Evaporator - E) in the cloud chamber. There is one circulator fan (C) provided on the back panel of the chamber for
369
maintaining the uniformity of atmospheric density distribution within the chamber space. Due to continuous air
370
circulation every volume element in the chamber has same humidity, temperature and particle density albeit particle
371
size may be variable at any space. To ensure uniformity in size of particles a prior size ranging is done after milling
372
of powder in a separate particle size analyzer. Fig. 2 shows three sensors for Humidity (HS), Temperature (TS) and
373
Pressure (VS). Near bottom of the chamber Pyrotechnic Cartridge Holder (PTCH) is fixed with a canopy for
374
performing experiment simulating cold cloud region. Canopy is provided as a shed for the burning flame of the
375
pyrotechnic cartridge so that any falling droplet does not extinguish it and also to quickly widen the dispersion of the
376
smoke generated by the burning cartridge so that it accelerates the quick distribution of the smoke particles
377
throughout the chamber space. There is one circular dry salt container(S) on the upper side of the chamber. The side
378
walls are 8 inch high, made of large size mesh – large enough to avoid any clogging (holes of 1.0 cm size diameter).
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There is one fan provided on the top of the container so that NaCl dust could rapidly be blown away through the
380
holes into the chamber while performing experiment, simulating warm cloud region. For the spray of brine solution
381
droplets in warm cloud region a Nebulizer (N) is provided close to salt container to spray droplets of nozzle size of
382
5µm or 10 µm as desired. Also there are intake filters provided at the inlet point of the air (AF). Chamber is
383
designed in such a way that desired pressure, temperature and humidity could be set initially only by the control
384
buttons provided on the front panel (right side) of the cloud chamber. Corresponding sensors would keep on
385
monitoring the parameters till they stabilize to desired values. Brief descriptions of different parts are presented
386
below in order of their experimental priority.
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3.1 Filter.
387
Filter is important component of cloud chamber. Several phenomena, e.g. inertial effect, diffusion, interception,
389
electrostatic, gravity, thermophoresis effect and Van der Waals force, etc., are commonly used to design filters.
390
First three of these, predominantly govern filtration mechanism. Nano fibres made of composites of glass, quartz,
391
nylon, silicon or silk polyester are used to make these high grade filters. Transparent Polyacrylonitrile fibres are
392
also used. Rectangular woven ‘nano-fibre mesh-sheets’ are obliquely joined in series to achieve the desired pore
393
size, in microns (Liu et al., 2017). In the present cloud chamber only filters of 1µm, 3 µm and 5 µm are installed.
394
Before the chamber is subject to any experiment it has to be ensured that the in-situ atmospheric aerosols are
395
removed so that they do not interfere in assessing the results of artificially introduced CCNs. Hence prior to
396
experiment, reasonably good degree of vacuum (as100% vacuum is not practically possible) needs to be generated
397
in the chamber by sucking out most of the chamber air. For this purpose a partial vacuum of 267hPa is generated in
398
the chamber. After this stage pressure in the chamber is increased to desired pressure level (e.g. 350 or more) at
399
which experiment is to be performed by intake of air through filters. As three filters of 1µm, 3 µm and 5 µm are
400
provided in the chamber hence if the experiment is to be performed with nucleating agents of sizes >3 µm or >5 µm
401
or >7 µm then filters of sizes 1 µm or 3 µm or 5 µm respectively, are to be used.
402
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3.2
Pressure Controller (Vacuum Pump)
404
Two heavy duty membrane pumps capable of continuous operation up to 30 days are installed with capacity of 100
405
liter with switch over function. Chamber is totally sealed with silicon fiber rubber seals on the main door panel and
406
double welding on the corners. It achieves lowest pressure of 200 mmHg (267 hPa). At the time of experiment pump
407
has to be stopped or else it would suck out the artificially released, CCN or IN from the chamber. Although all
408
precautions against leakage have been taken but despite that at very low pressure, due to strong inward pressure
409
gradient, after the motor is stopped, very slow inward air leakage remains unavoidable and the pressure gradually
410
increases at the rate of 30mmHg/Hr or (40hPa/hour). It is not clear that after motor is stopped what could possible
411
passage for the air entering the chamber to increase the pressure at very low pressure. Nevertheless possibly there
412
could be only two inlet/outlet. Either it could be the filter valves or it could be the suction pump valves, though both
413
of them are tightly closed as the motor is stopped. Hence it could be the mechanical limitation of the chamber.
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414
Any possible aerosol leaking along with the atmospheric air entering the chamber could be ignored as the aerosol
415
generations by the cartridges are of the order of 1010 to 1016 per m-3 for each gram of solution as observed in the
416
chamber of De Mott, 1982. In our chamber, too, same order of nuclei could be presumed which is expected to be
417
predominantly of very high order than the ambient aerosols which might possibly get sucked into chamber along
418
with
419
As any seeding experiment in the chamber does not last more than 30 minutes (Appendix A) from the time of
420
release of the CCNs till the luxmeter reading reverts back to ≈ 250 lx hence it reasonably meets the accuracy
421
requirements for seeding test experiment.
422
Rate of pressure increase after the motor is stopped is not same for all the pressure gradients. The lower is the
423
pressure the higher is the leakage rate. Between 300 to 400 hPa after the motor is stopped pressure rises at the rate of
424
≈40 hPa/hr, between 400 to 500 hPa it rises at the rate ≈20 hPa/hr and between 500 to 600 hPa rate of rise of
425
pressure further reduces to ≈ 10 hPa/hr. Below 600 hPa even after the motor has been stopped there is no pressure
426
increase displayed by the chamber and it remains steady. Highest rate of rise, therefore, is of the order of ≈40
427
hPa/hr. Hence within 30 minutes of experiment the rise of pressure would be of the order of ≈20 hPa only.
slowly
leaking
in
at
very
low
pressure.
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Temperature Controller(Refrigeration)
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Refrigeration system can achieve controlled temperature in the range from -250C to +500C with prescribed limit of ±
431
30C of stability. Environment friendly refrigerant(R-404A) has been used. Max operating current could be 5 Amp
432
and the compressor has min/max operating pressure of 200/300 psi.
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433 434
Fig. 4 shows the single stage refrigeration unit line diagram of the chamber. Thermostat is used for temperature
435
control. Special precautions are taken to ensure that air going/coming to/from the chamber is not in direct contact of
436
the heating coils.
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439
Two water humidity generators are used for humidification. Electric heater of 2.5 KW is used for heating water for
440
its evaporation inside the chamber. Heating coil inside the chamber is made of copper but it not in contact with the
441
water reservoir storing the water above. Minimum 2 liter of distilled water is needed in the container. Chamber can
442
provide the humidity in the range of 30% to 99.9% with stabilization in the range of ± 3%.Digital Humidity
443
Controller is used which can sense the Relative Humidity (RH) in the range of 0.0 to 99.9% RH. Resolution of
444
sensor is 0.1%RH. If humidity goes above the set value water heater automatically stops.
445
Temperature and humidity sensors are independent to each other. Temperature is controlled by the refrigeration unit.
446
The attached sensor stabilizes of desired temperature under control by sending suitable signals to the refrigeration
447
process, irrespective of humidity or pressure values. Fluctuations are within the range of ± 30C. Similarly humidity
448
sensor stabilizes the chamber humidity generated by the evaporator in the range of ±3%. These are the instrumental
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limitations of present cloud chamber. With high quality of quick response sensors the fluctuation range can be
450
narrowed, in future.
451
3.5 Variability of pressure temperature and humidity.
452
Pressure temperature and humidity are fixed as per the requirement of the experiment. They are designed, in
453
conformity with the actual atmospheric conditions where they keep changing on day to day basis. At any pressure
454
level based on the observed temperature and humidity they both are fixed prior to experiment. They have separate
455
independent controllers. Temperature fluctuation of ±3°C is the maximum limit. It means that if we set the
456
temperature at – 120C then it may slowly vary between -130C to -110C (87%) or at times it may be between -140C to
457
-100C (12%). Rarely (1%) may it go even up to -150C to -90C, but never more than this. Fluctuations are in the
458
interval of 30to 60 seconds. Similar is the case of humidity. Humidity also keeps of varying slowly from its fixed
459
value within the interval of 30 to 60 seconds. In any case mean of the variability taken over any short time interval
460
always remains the desired value. Hence they are not likely to affect the result, significantly. Nevertheless with more
461
advance technology there are scopes of installing more sensitive controllers to narrow the fluctuation range.
462
3.6 Chamber Fan
463
Fans have vertical blades and they rotate around a vertical axis.
464
3.7 Nuclei dispersion Units
465
3.71 Warm Region Dispersion. Fig. 1(b) top right shows the Dry salt powder dispersion container. Notice
466
perforated wall to disperse dry salt by blowing it away by fan.
467
It is located in the upper region of the chamber so that salt particles either remain suspended or gradually fall down
468
by gravity through the humid air. Nebulizer is used for spraying atomized sodium chloride solution droplets. It
469
operates on ultrasonic frequency of 1.7 MHz (±10%) Maximum capacity of small atomizing cup is 150 ml and that
470
of big cup is 350 ml. It atomizes at the rate of 4 ml/min and can continuously work for four hours. Particle sizes
471
range from 0.5 to 5µm. Its water tank capacity is 300ml and power consumption 50VA, Power supply voltage
472
should be 220v; 50Hz.It is located in the upper region of the chamber so that atomized droplets either remain
473
suspended or gradually fall down by gravity through the humid air.
474
3.72 Cold region Dispersion. Fig.1(b) shows the pyrotechnic cartridge burning stand.
475
It is located in the lower region of the chamber so that smoke rises above after getting released from cartridge and
476
fills the chamber. Canopy provides protection to the burning cartridge from any falling rain , drizzle droplet or
477
hydrometeors over it. It also helps spread the fumes.
478
3.8 Electrical and mechanical features and control panel
479
Three phase power of 415V (±10%) and 50 Hz AC supply is needed for the cloud chamber. Its exterior and interior
480
body is made of Satin finish Stainless Steel 304 quality 20 SWG. Chamber is heat insulated by non-inflammable
481
Ceramic/Rockwool of 125 mm thick fiber pad. The pilot light indicators are significant during the operation of the
482
cloud chamber. The meaning of the abbreviations used on the front panel control are explained in table-1 and table-
483
2.
484
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Table-2
485
For hail control we only need to know that how fast and how effectively nuclei induce cloud formation so
487
that Vapor Water Content (VWC) of the cloud is divided in maximum number of small droplets
488
(Sulakvelidze, 1969). Chamber is, therefore, not designed to observe the characteristic of the cloud e.g ice
489
phase or liquid phase or mixed phase. The chamber is also not installed with particle size measurement
490
instrument or size spectrometer (e.g. electrostatic precipitator collection foils for photo micrograph analysis
491
or disdrometer) to know spectrum of cloud particle ensembles. Instead a lux meter serves our objective.
492
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4.0 Making of AgI Pyrotechnic Cartridge for Efficient Ice Nucleation
494
Edwards and Evans(1960) studied the ability of silver iodide particles to act as ice nuclei under controlled conditions
495
of temperature and humidity. They noted that ≈100 Å of effective radius is largely ineffective at ≈ 100% humidity
496
whereas 60 to 75 Å of effective radius are active as freezing nuclei between -8 to -90C and 90 to 100 Å between -6
497
to -70C. Koenig(1964) had noted that AgI particles of several microns in diameter are also not uncommon in
498
pyrotechnic smoke. AgI particles are also photosensitive (Burley and Herrin, 1962) hence different compounds
499
have been attempted to obtain photo resistant suitable particulate size for getting effective nucleation by the
500
burning pyrotechnic cartridge. Ice nucleation by cyclic compounds (Head, 1962) and IN through the combination of
501
AgI-NaI (Mossop and Jayaweera, 1969) had been attempted, since long. DeMott (1982, 1995) had the prime
502
objective to test the efficiency of various compound mixtures in producing maximum IN nuclei for condensation,
503
primarily for the artificial rain making campaigns. He found that mixed AgI – AgCI nuclei display effectiveness
504
values which are one order of magnitude larger at -120C and three orders of magnitude larger at -60C in comparison
505
to the AgI nuclei generated from the AgI'NH4I - acetone - water solution combustion system but he also observed
506
that AgI-AgCl nuclei are relatively slow. For 90% production in 1.5 gm -3cloud it will take 20-30 minutes. Hence,
507
though effective but it cannot become an efficient formulation. Although seeding operation and its efficiency
508
towards cloud formation is significant in all weather modification campaigns, it is extremely important, especially in
509
clouds treated during hail mitigation operations, that seeding agents provide quick and effective nucleation (e.g.,
510
ASCE 2015; Kumar and Pati, 2015; Kumar, 2017).
511
The best pyrotechnic formulation, especially suited for hail control programme, tested in our cloud chamber, is
512
shown in Table – 3. The most suitable formulation was achieved after ten different pyrotechnic cartridges with
513
varying formulation were tested inside the cloud chamber. For details refer Appendix-A.
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Table 3
515
3.0 gm formulation milled to ≤5µm size powder is filled into perforated cylindrical asbestos shell and tightly packed
516
using mechanical press. After all the materials are tightly packed inside an 8mm nicrome wire is inserted inside. The
517
cartridge is then wrapped by transparent tape so as to avoid the contact of moisture with the pyrotechnic
518
formulation. Both the side of the cartridge case is completely sealed by the tape. This cartridge takes less than 15
519
seconds to completely burnout into smoke.
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Reutova et al (1996) analyzed the NH4Cl based pyrotechnic cartridge and noted that during combustion it ingests not
521
only particles of AGI but also HCL and Cl- ions in gaseous phase associated with AgI particles. Gaseous NH3 follow
522
them. The particles of AgI with absorbed layer of Cl- (HCl) and free HCl are able to condense the water vapour
523
owing to strong hygroscopic properties that effect on the cloud processes. Getting into the small cloud droplets or
524
condensing the vapor they are able to create the high concentration of Cl- in ambient water coat. Complex process
525
between Ag, Cl- and NH3 finally leads to increase in solubility of AgI. It was concluded that beside AgI other
526
components also help supports sorption, freezing and sublimation together as observed by Edwards and Evans
527
(1960) in a cloud chamber nucleation process.
528
4.1 Initial conditions of the chamber.
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Initial condition of the chamber with respect to temperature, pressure and humidity has to be fixed as
530
per the requirement of the experiment. For example if pyrotechnic cartridge has to be tested then
531
temperature could be fixed in subzero range of – 40C to – 190C and pressure could be accordingly
532
adjusted based on the actual atmospheric conditions. Humidity could be also fixed varying from 90%
533
to 101%.Similarly if the warm cloud seeding agent e.g. Na Cl or Urea etc are to be tested then
534
chamber initial conditions cloud be fixed anywhere in the range temperature + 100C to 00 C and
535
pressure could be accordingly adjusted based on the actual atmospheric conditions.
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536
Prior to experiment we have also to ensure that the chamber is free from any in situ aerosols. As perfect
538
vacuum is not possible it is important to achieve near vacuum in the cloud chamber for the same. To
539
achieve this chamber is initially brought down to 267 hPa with the help of suction pump. This will help
540
remove any extraneous aerosols to a greater extent, though not completely. Left over aerosols at 267
541
hPa inside the chamber could be negligibly small quantity and may not cause significant error in the
542
lux meter reading. Lux meter reading at this stage shows ≈ 250 Lux. After this step the chamber
543
pressure is brought up to desired level as per the need of the experiment by slowly intake of desired
544
atmospheric air through any one of the three filters of 1µm, 3 µm and 5 µm. If the experiment is to be
545
performed with IN agents of sizes >3 µm or >5 µm or >7 µm then filters of sizes 1 µm or 3 µm or 5 µm
546
respectively are to be used. However from the practical point of view, the smaller is the hole the larger
547
is the experiment set-up time. In all future application it would be the choice of the scientist, based on
548
the demand of the type of experiment, as to what cut off would be desirable. Accordingly filter selection
549
may be made. Once the chamber aerosol sizes are fixed then vacuum sensor guides it to the desired
550
pressure level as per the need of the experiment. Lux meter reading continues to sustain at ≈ 250 Lux.
551
Probability of existence of cloud droplets in the chamber before the experiment begins, is not totally
552
zero because of two reasons. First if the experiment is to be performed with the release of 10µm seeding
553
agent then while bringing the pressure from 267hPa to desired pressure level the inflow into the
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chamber with 5 µm filter would permit aerosols of size ≤ 5µm only. Hence condensation may take
555
place but over lower size aerosols only. Secondly since chamber is not totally evacuated to get 100%
556
vacuum hence some negligibly small number of aerosols might remain inside the chamber to cause
557
condensation. Both the causes would induce small effect only; this had been observed during all the
558
experiments and initial transparency remained close to 250 lux if not exactly 250lux.That is why we
559
maintained that initial lux meter reading would be either ≈ 250 Lux or less. This is as per the luminosity
560
provided by the LED light (250dBZ) source minus the extinction provided by in situ small aerosols(say
561
€ dBZ). During the experiment, therefore, our last regained luminosity should be 250- € dBZ to
562
account for this error.
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563 5.0 Experimental Details
565
Cloud chamber simulates one particular level of atmosphere. Repeated experiments have to be done in the chamber
566
for different levels to get the integrated result for entire cloud.Table-4 presents these results for quasi International
567
Standard Atmosphere. The parameters inside the cloud chamber were set as per the desired requirements. Columns
568
1, 2, 3, 4 of table-4 show the date wise details of observations. Luxmeter readings at 0th min, 5min, 15min and 30
569
min are mentioned in columns 5, 6, 8 and 10 respectively. Column 7 represents the Rate of Nucleation (RN) from 0th
570
min to 5th. As explained in section 2.1 Rate of Precipitation (ROP) is represented by Column 11.
571
represents the transition period when condensation and precipitation both the processes are expected together albeit
572
rate of precipitation apparently dominates rate of condensation during this phase, too.
Column 9 only
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573
Experimental details are presented in appendix – A. It may be inferred that the higher is the difference the faster in the process. The high difference values in columns 7 shows faster spontaneous nucleation process. Similarly higher rate of precipitation could be indicated by the higher values in columns 9 and 11 during the corresponding time periods. To view integrated picture of performance of the cartridge inside cumulus cloud from 522hPa (-4.80) up to 368.7hPa (-200C) layer wise results are stacked up in a tabular form in table 4. Each layer in table 4 is discrete layersample from the continuum structure of cloud atmosphere.
580
The difference of luxmeter readings between 5 min to 0 min, 15 min to 5 min, and 30 min to 15 min were plotted for
581
the standard atmospheric profile for varying temperature in fig 5 and for varying pressure in fig 6.
582
Fig. 5
583
Fig. 6
584
It was just a trial and error method that we discovered that six order fit displays highest coefficient of determination
585
values. For lower order polynomials, the value incessantly decreases. Cause of sinusoidal variation is not clear.
586
Simultaneous variability of pressure and temperature in actual atmospheric conditions as any drop-cartridge is
587
falling from higher level to lower levels may be, possibly, attributed to this sinusoidal behavior. Albeit result have to
588
be further examined with similar experiments in other cloud chambers, too, for cogent acceptance of the argument.
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The trend curve for rate of Nucleation- RNL05 (blue line)is shown on figure 5 and the trend curve of rate of
590
precipitation(RPL10) which predominates over nucleation during the transition period5 to 15 min interval is indicated
591
by violet line (figure 5) . The rate of precipitation (RPL15) between 15 to 30 min intervals is indicated by the green
592
line in this figure. It may be noted that the nucleation process is faster at increasingly lower temperature and
593
precipitation process decreasingly slows down at lower temperature. It has been already verified in past that
594
threshold of AgI seeding activity is near -50C and number of active nuclei increases by order of magnitude for each
595
drop in temperature by 3.5 to 40C down to -150C or -200C (Dennis(1980). Trend line equations for RNL05, RPL10 and
596
RPL15 are shown by the linear regression equations 8, 9 and 10 respectively.
598
RPL10 = 3.1672T + 148.57
599
RPL15 = 2.0029T + 50.119
600
(9)
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RNL05 = -3.0185T + 31.093
(10)
(11)
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Where,
601
RNL(Time interval in min)= Rate of Nucleation in Lux
602
RPL(Time interval in min) = Rate of Precipitation in Lux
603
T= Temperature in 0C
Taking point of intersections of (9) and (10) and that of (9) and (11) we get -190C and – 3.80 C respectively. Hence
605
we may infer that both nucleation and precipitation attain the optimal rate values, between -190C and – 3.80 C.
606
Result is in close conformity with accepted range of optimum results, in actual atmosphere, by AgI – NH4I and AgI
607
– NaI nuclei between – 80C to –160C - former being little more than the later, (Kumar, 2017). With similar colour
608
scheme results could be obtained in the graph plotted against the pressure change in the standard atmosphere. Trend
609
line for rate of nucleation is given by equation (12) which indicates the trend of L2-L1. Rate of precipitation (L3-L2)
610
up to 15 minutes and that up to 30 minutes are shown by the linear regression equation (13) and (14) respectively.
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604
RPL10 = 0.3482 P - 46.825
612
RPL15 = 0.1985 P - 63.789
613 614
AC C
RNL05 = -0.3135 P + 209.04
611
Where,
615
RNL(Time interval in min) = Rate of Nucleation in Lux
616
RPL(Time interval in min) = Rate of Precipitation in Lux
617
P= Pressure mmHg
(12) (13) (14)
18
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618 Points of intersection of (12) and (13) and (12) and (14) indicate that between 385.86 mmHg and 532.86 mmHg rate
620
of nucleation and precipitation achieved the optimum values together. The mmHg units may be converted assuming
621
International Standard Atmospheric conditions. Similar experiment can be performed by taking any one day’s
622
atmospheric data for pressure and temperature for different layers. Result indicates that in actual atmospheric
623
condition rate nucleation incessantly slows down at lower levels in atmosphere but at higher atmospheric levels it is
624
faster. On the other hand rate of precipitation process is faster at lower levels and incessantly slows down at higher
625
levels in atmosphere. In the present case one may infer that optimum range of pressure where precipitation and
626
nucleation both are optimum is between ≈ 385.86 mmHg and 532.86 mmHg levels. This result is open to
627
verification in future atmospheric seeding experiments.
628
It may be further noted from figures (12) and (13) that rate of nucleation in the standard atmosphere shows a
629
sinusoidal behavior.
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619
Table 5
630 631
Table 5 shows six order polynomial best fit for the rate of nucleation vs temperature (L2-L1) variation in
632
International Standard Atmosphere (ISA). Rate of precipitation vs temperature (L3-L2) after 15 min and 30 min
633
(L4-L3) are also shown in table. Last column shows high degree coefficient of determination. Table 6
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634
Table 6 shows six order polynomial best fit for the rate of nucleation vs pressure (L2-L1) variation in International
636
Standard Atmosphere (ISA). Rate of precipitation vs pressure (L3-L2) after 15 min and 30 min (L4-L3) are also
637
shown in table. Last column shows high degree coefficient of determination.
638
6th order best fit polynomials in tables 5 and 6 for L2-L1 i.e. Rate of Nucleation(RN), are having very high
639
coefficient of determination (≈ 0.9) hence could also be used as statistical prediction model.
640
6.0 Scope of Improvisation
641
Jonathan et al (2007) used Spontaneous Raman scattering and Stimulated Raman spectroscopy for the determination
642
of droplet size with nanometre accuracy and can allow the characterization of near-surface composition. Takahama
643
et al, (2011) had used Fourier transform infrared (FTIR) spectroscopy for organic functional groups (OFG) to
644
separate burning and non-burning forest sources of the measured organic aerosol. Testing of the efficiency of
645
seeding agents, described in the present cloud chamber is currently based on simple optical luxmeter measurements.
646
It is hoped that in future, with the addition of multispectral spectroscopy equipments in the chamber, the scope of
647
researches in this chamber could be multiplied many fold.
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648 649
7.0 Conclusions.
19
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650
i.
This cloud chamber is specifically designed and fabricated to simulate the tropical atmosphere for testing
651
different IN. Optional pressure (<350hPa), temperature ranges (-150 to + 500C) and humidity (30 to 99.9%)
652
have been provided to simulate any particular level’s atmospheric conditions, with in cloud.
653
ii.
In the cloud chamber Pressure could be stabilized at any optional value within acceptable rise margin of 40hPa/hr. Temperature remains stabilized in the range of ± 30C and Humidity sensor keeps it stabilized in
655
the range of ± 3% within 30 to 60 seconds. Humidity can be measured up to 99.9% by digital sensors with
656
resolution of 0.1% RH.
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654
657
iii.
Environment friendly compressors have been used for refrigeration.
658
iv.
Hypothesis of quantitative assessment of cloud formation is based on the assumption that drop in
illumination is directly proportional to particulate concentration per unit volume. Albeit hypothesis
660
is reasonably valid for small size of droplets (≤ 20 µm) it is still uncertain for the solid phase or
661
mixed phase of the droplets e.g. when super cooled liquid droplets and ice crystals are together in
662
the ensemble of nuclei. Fragmentation of a freezing drop in the forms of splintering, shattering, or
663
bursting has been known between the o to -200C (Cheng, 1970; Harris-Hobbs and Cooper, 1987;
664
Yano and Hillip, 2011). Nevertheless further study and experimental verification is needed for
665
applying the exact correction factor (Korolev, et al., 2012).
668
If drop in luminosity is d and total concentration of particulate matters is Cp per unit volume then d
667 vi.
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α
Cp
Rate of Nucleation(RN) is assessed on the hypothesis that Rate of Nucleation (RN)
669
α
L5 - L0
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659
670
Where L0 is the lux meter reading at the time of release of IN and L5 is lux meter reading after 5 minutes of
671
the release of IN.
672
vii.
Circulation fan provided inside the chamber relentlessly keeps circulating the cloud mass with in the chamber, hence cloud particle makes several round of the chamber space during the process of its growth
674
by coalescence or by Bergeron process resulting into growth of cloud droplet . Precipitation could be
675
drizzle, rain or hydrometeor. For Rate of Precipitation (ROP) if the Lux meter reading after 15 Minutes of
676
the release of IN is L15 and after 30 minutes interval if it is L30 then it may be hypothesized that
EP
673
678
viii.
AgI Pyrotechnic cartridge formulation as mentioned in table 3 generates effective cloud seeding nuclei
performed in the standard atmospheric conditions. The results have got to be validated for other
681
combination of temperature and pressure in actual atmosphere.
682 ix.
The rate of nucleation within 5 min of the release of nuclei shows higher values at low temperature (≈ 200C) and slower values at higher temperature (≈ - 50C).
684
686
L30 - L15
and range of pressure between 532.86 and 386.76 mmHg (≈ 710 and 514hPa). Experiments were
680
685
α
which works in the actual atmospheric conditions optimally in the range of temperature -3.70 C and -190C
679
683
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Rate of Precipitation (ROP)
677
x.
The rate of precipitation shows higher values at higher temperature (≈ - 50C) and slower values at lower temperature (≈ - 200C) . 20
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687
xi.
Nuclei. This needs to be reexamined for different size of cloud chamber.
688 689
The process of nucleation and precipitation seems to be complete within 30 minutes after the release Ice
xii.
Six order polynomial successfully simulates the nucleation process for temperature vs luxmeter reading and also pressure vs luxmeter reading. In both these cases it is observed that coefficient of determination
691
shows a very high values. It might be caused due to simultaneous change in temperature and pressure in
692
actual atmosphere.
693 694 695
xiii.
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Six order polynomials in tables 5 and 6 for L2-L1 are having high very coefficient of determination (≈0.9) hence could also be used as statistical prediction model for condensation and rate of condensation.
Acknowledgement.
Author is deeply grateful to Indian Council of Agriculture Research’s programme on National Initiative of
697
climate Resilient Agriculture (NICRA,) for funding this project entitled “Hailstorm Management Strategy
698
in Agriculture”. Author is also grateful to D. Jaykumar,SRF, Debprasad Pati, JRF and Shweta Bhardwaj,
699
JRF, NICRA Project for helping me in various operations/experiments during the fabrication and
700
development phase of cloud chamber. Thanks are due to MIT World Peace University, Pune, Maharashtra,
701
India for providing the new building for the Hailstorm Laboratory. Author also expresses sincere thanks
702
also to both the referee for making valuable suggestions.
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703 References.
705
Am. Soc. Of Civil Eng., (ASCE) 2015, Guidelines for operational hail suppression programs (39-15),
706
Standards ANSI/ASCE/EWRI 39-15, pp 62.
707
Am. Met. Soc.(AMS), 1952, Ed. Ralph E. Huschke, Glossary of Met., Boston, Massachusetts, pp 397-398.
708
TE D
704
Burley G and Herring D.W., 1962, Effect oon Silkver Iodide particles exposed to light, J. of Appl.
710
Meteoro., Vol. 1, 355-356.
711 712 713
Cheng, Roger J., 1970. Water Drop Freezing: Ejection of Micro droplets, Science, New Series, Vol. 170, No. 3965 ,Dec. 25, pp. 1395-1396, American Association for the Advancement of Science. (URL: http://www.jstor.org/stable/1730870).
714 715 716 717 718 719 720 721 722 723 724 725 726 727 728
Chernov,A. A., 1984.Modern Crystallography III-Crystal Growth ~Springer, Berlin.
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709
Colin D. O’Dowd and Waner Paul, 2007, Nucleation and Atmospheric Aerosols, 17th Int. Conf., ICNAA2007, Galway, Ireland, pp-1255. Das Gupta, N.N., Ghosh S.K. 1946.A report on the Wilson cloud chamber and its applications in physics. Reviews of modern physics 18 (2): 225–365.
DeMott J. Paul, 1982. A characterization of mixed silver iodide-silver chloride ice nuclei. Atmospheric science paper no. 349, Department of Atm. Sc., Colorado State University, CO, U.S.A. DeMott J. Paul, 1995, Quantitative descriptions of ice formation mechanisms of silver iodide-type aerosols, Atmospheric Research 38, 63-99
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Dennis A. S. 1980. Weather modification by cloud seeding, Int. Geophysical Ser., Vol. 24, Acad. Press, NY, 1980, pp 107-110.
746 747 748
Harris-Hobbs, R. L., and W. A. Cooper, 1987: Field evidence sup-porting quantitative predictions of secondary ice production rates.J. Atmos. Sci.,44,1071–1082.
749 750
Head, R.B., 1962, Ice nucleation by some cyclic compounds, J. of Phys. And Chem. Of solids, Vol. 23, Issue 10, Oct., pp 1371-1378.
Edwards G.R. and Evans L.F., 1960. Ice Nucleation by Silver Iodide: I. Freezing vs Sublimation, J. Meteo., Vol. 17, 627-634.
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Fukuta N. 1969. Experimental studies on the growth of small Ice crystals, J. Atm. Sc., May, Vol. 26, pp522-531. Garvey. D. M., 1975. Testing of Cloud Seeding Materials at the Cloud Simulation and Aerosol Laboratory, 1971-1973. J. Appl.Meteor.,14, 883-890. Grant and Steele, 1966.Weather Modification by cloud seeding,,Arnett S Dennis. Int. Geophysical Ser., Vol. 24, Acad. Press, NY, 1980, pp 108.
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Hallett, J. and Mossop, S.C., 1974, Production of Secondary Ice Particles during the Riming Process. Nature, 249, 26-28.
751
Jonathan P. Reid , Helena Meresman , Laura Mitchem & Rachel Symes, 2007, Spectroscopic studies of the size and composition of single aerosol droplets, International Reviews in Physical Chemistry, Volume 26, 2007 - Issue 1, Pages 139-192
755 756
Singh H, Datta R K, Chand S, Mishra D, Kannan B,2011. A study of hail storm of 19th April 2010 over Delhi using Doppler weather radar observations, Mausam, Vol 62, Number 3, 433-440.
757 758 759
Summers, P.W., Mather G.K. and Treddenick, D.S., 1972, The development and testing of an airborn Droppable pyrotechnic flare system for seeding Alberta Hailstorms, J. of Appl. Metor., June, Vol.11, 695703.
763 764 765
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Koenig L. Randall,1964, Some chemical and physical properties of silver-iodide smokes, J. Appl. Meteor., Vol.3, 307-310.
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752 753 754
KumarP.,2017. Hailstorm Prediction, Control and Damage Assessment. Second edition, BS Publication and
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CRC Press,Vol. 1, ISBN: 978-81-7800-248-4. pp-286.
767
Kumar P. and Debaprasad, Pati, 2015.Radar Imageries Information Extraction and its use in Pre-Hail
768
Estimation Algorithm, Mausam, 66,4,October,698-712.
769 770 771
Korolev, A., Shashkov A. and Barker H., 2012. , Parameterization of the Extinction Coefficient in Ice and Mixed-Phase Arctic Clouds during the ISDAC Project, Environment Canada, Cloud Physics and Severe Weather Research Section, Toronto, Canada. 22
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Liua X. Y., 2000.Heterogeneous nucleation or homogeneous nucleation? Journal of Chemical Physics, Volume 112, Number 22 8 June..
Liu Guoliang, Manxuan Xiao, Xingxing Zhang, Csilla Gal, Xiangjie Chen, Lin Liu, Song Pan, Jinshun Wu, Llewellyn Tang,Derek Clements-Croome, 2017, A review of air filtration technologies for sustainable and healthy building ventilation, Sustainable Cities and Society 32, 375–396
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772 773 774 775 776 777 778 779 780 781 782 783 784 785
Mahen Konwer, Maheshkumar, R.S., Kulkarni J.R., Freud E, Goswami B.N. and Rosenfeld D., 2012, Aerosol control on depth of warm rain in convective clouds, J. of Geophysical Res., Vol. 117, pp-1-10.
Matteo Leoneand Nadia Robotti, 2004. A note on the Wilson cloud chamber (1912), European Journal of Physics, Volume 25, Number 6 , 14 September.
788
Mason, B.J., 1957, The physic of clouds, Chs 1-4.
789
McDonald, J.E., 1953, Homogeneous nucleation of supercooled water drops, J.Met., pp. 416-433.
790 791
Mossop, S.C., and Jayaweera, K.O.L.F., 1969, AgI-NaI Aerosols as Ice Nuclie, J. of Appl. Meteo., April, pp-241-244.
792 793
Pruppacher, H.R. and Beard, K.V., 1970, A wind tunnel investigation of the internal circulation and shape of water drops falling at terminal velocity in air, Quart. J. R. Met. SOC. (1970), 96, pp. 247-256.
794 795
Pruppacher, H.R. and Klett James D., 2010. Microphysics of cloud and Precipitation, Atmospheric and Oceanographic Sciences Library, Vol. 18, Spiringer. Ch. 7,pp 191-209 & ch. 9, pp 287-355.
796 797
Reutova, T.V., Zhinzhakova, L.Z., Chernyak, M.M., and Shvedov, S.V., 1996, Nucleation and Atmospheric Aerosols, 14th Int. Conf.,ICNAA-1996, pp-885-888.
798 799
Rogers R. R., and Yuan M.K., 2006, A short course in cloud physics, IIIrd ed., Butterworth-Heinemann Pub.
800
Sohnel O. and Mullin, J. W.1978. J. Cryst. Growth 44, 377.
802 803 804 805
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Skripov, V. P.,1977. In Current Topics in Materials Science, edited by E. Kaldis and H. J. Scheel ~NorthHolland, Amsterdam,. 327–378.
Sulakvelidze G.K., 1969. Rainstorm and Hail, IPST Press, Jerusalam.
806 807 808 809 810
Takahama S., Schwartz, R. E, Russell L. M., Macdonald A. M. Sharma S. and Leaitch W. R., 2011, Organic functional groups in aerosol particles from burning and non-burning forest emissions at a highelevation mountain site, Atmos. Chem. Phys., 11, 6367–6386, www.atmos-chem- phys.net/11/6367/2011/ doi:10.5194/acp-11-6367-2011 23
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Vonnegut, B., 1949. Nucleation of supercooled water clouds by silver iodide smoke. Chem. Rev., 44, 277-
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289.
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Wang P. K. and Pruppacher H. R.1977. Acceleration to terminal velocity of cloud and rain drops, March, Vol. 16, J .of Appl. Met., 275-280.
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Witt A , Eilts M. D., Stump G. J., Johnson J. T., Michell E. D., 1998, An enhanced hail detection algorithm for the WSR-88D, Wea. and Forecasting, 13, 2, 286-303.
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Yano, J.-I. and Hillip, V. T. J. P, 2011, Ice–Ice Collisions: An Ice Multiplication Process in Atmospheric Clouds, Vol. 68,February, pp-322-333
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AMS, U.S.A.2015, Met Glossary: http://glossary.ametsoc.org/wiki/Nucleation
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ANSI/ASCE/EWRI 2015 hail suppression document. http://www.asce.org/templates/publications-book-
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detail.aspx?id=15783
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EPA, U.S.A. 2017 https://www.epa.gov/pm-pollution/particulate-matter-pm-basics#PM
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Towards Design and Development of Isothermal Cloud Chamber for Seeding
2
Experiments in Tropics and Testing of Pyrotechnic Cartridge
3
Tables
4
Table-1 Front Panel Controls
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1
Description
POWER ON
Light glows when 3 phase mains supply is properly connected in mail sequence.
DOOR OPEN
Light glows when chamber doors are opened or are not properly closed.
O/L CH. FAN
Light glows when Compressor fan is turned off in case of over loading.
O/L COMP 404
Light glows when Compressor R-404 is turned off in case of excessive overloading on
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Pilot Lights
compressor.
Light glows when condenser fan R-404 is turned off in case of over loading
H.P. 404
Light glows when Compressor R-404 is turned off in case of discharge pressure of
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O/L COND. FAN
compressor decreases below the specified limit.
L.P. 404
Light glows when Compressor R-404 is turned off in case of suction pressure of compressor decreases below the specified limit.
Light glows when Vacuum Pump 1 gets turned off in case of excessive overloading on
EP
O/L VACCUM PUMP
VACUUM
Light glows when vacuum is on
DE VACUUM
Light glow when vacuum is being released
OVER TEMP
Light glows when temperature inside the chamber increases beyond the set limit.
LOW WATER
Light glows when water is low in humidifier
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5
6
7
Vacuum Pump 1.
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8
9
Control Switches of the Cloud Chamber
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Table-2
10
Used to switch on Air Flow
Heat ON/OFF
Used to switch on Heater
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Air ON/OFF
Cool ON/OFF
Used to switch on Cooling
CH. LIGHT ON/OFF
Used to switch on the Chamber light
CH. LIGHT (LUX)
Used to switch on the Luxmeter light
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ON/OFF
POWDER
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DISPERSION
Used to trigger the burning of pyrotecnique cartridge
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AGI ON/OFF
Used to start Powder Dispersion fan
NEBULIZERS
Used to start Nebulizer
HUMIDITY ENABLE
Used to switch on humidifier
VACUUM ENABLE
Used to switch on Vacuum Pump
AUX
Auxiliary Switch
AUX
Auxiliary Switch
EMERGENCY STOP
Used to switch
11
12
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Table 3: AgI Pyrotechnic Cartridge chemical Formulation
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Pyrotechnic cartridges composition Material Percent by Weight Silver iodate 45.0 Potassium perchlorate 27.0 Magnesium 20.0 Nitrocellulose 4.0 Triacetin 4.0 13 14 15 16
20 21 22 23 24 25 26 27 28 29
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Table-4. Results of experiments performed inside the cloud chamber with same formulation of pyrotechnic cartridge as in table-3, at ≈100% humidity and varying temperature and pressure, as per actual atmospheric conditions (vide quasi International Standard Atmosphere). To view integrated picture of performance of the cartridge inside cloud from 522hPa (-4.80) up to 368.7hPa (-200C) layer wise results are stacked up in a tabular form. These layers are the “discrete - samples” from the continuum structure of atmosphere with respect to pressure vis-à-vis temperature.
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Date (dd/mm/yy)
Pressure (mmHg)
Temperature (0C)
Humidity (%)
Lux meter Readings(LUX)
At 0 min L1
At 5th min L2
2
3
4
368.7
-20.40C
99.9%
11.5
112
100.5
214.5
2
10/1/14
376.0
-19.70C
99.9%
55
154
99
201.5
3
15/1/14
395
-18.70C
99.9%
20
104.5
84.5
204.5
4
15/1/14
411.7
-16.50C
99.9%
16
96.5
80.5
207
5
17/1/14
429
-14.70C
99.9%
70
49.5
191
7
23/1/14
446
-12.70C
99.9%
40.5
110
69.5
194
8
24/1/14
464
-10.80C
99.9%
31.5
102
70.5
204.5
9
4/2/14
483
-8.80C
99.9%
14.6
82.2
67.6
211
10
7/2/14
502
-6.80C
99.9%
31
70
39
205
11
11/2/14
522
-4.80C
99.9%
13.7
68.2
54.5
198
33 34 35 36 37 38 39
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7
Trans ition perio d
8
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1
20.5
L3-L2
At 15th min L3
10/1/14
31
6
Lux meter Readi ngs(L UX)
1
30
5
L2-L1 (RN)
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Sr.No
9
Lux meter Readi ngs(L UX)
L4-L3 (ROP)
At 30th min L4
10
11
220 102.5
5.5 220
47.5
18.5 212.5
100
8 211.5
110.5
4.5 224
121
33 227.5
84
33.5 229.5
102.5
25 242
128.8
31 236
135
31 241
129.8
43
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Table 5: Polynomial and coefficient of determination of the best fit curve for Temperature vs Luxmeter difference reading Six Degrees Polynomial Equation
L2-L1
y = 0.0009x6 + 0.0704x5 + 2.3005x4 + 38.415x3 + 342.76x2 + 1533.3x + 2713.3
R² = 0.889
L3-L2
y = 0.0017x6 + 0.1237x5 + 3.6122x4 + 53.321x3 + 417.08x2 + 1635.7x + 2645.7
R² = 0.6788
L4-L3
y = -0.0006x6 - 0.0472x5 - 1.4471x4 - 22.424x3 - 183.82x2 749.11x - 1142.5
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42 43
48 49 50 51 52 53 54 55 56 57
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coefficient of determination
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Temperature vs Luxmeter difference reading
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R² = 0.8496
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Table 6: Polynomial and coefficient of determination of the best fit curve for Pressure vs Luxmeter difference reading Pressure vs Luxmeter difference reading
Six Degrees Polynomial Equation
L2-L1
y = 9E-10x6 - 2E-06x5 + 0.0025x4 - 1.4163x3 + 455.45x2 77831x + 6E+06
coefficient of determination
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58 59
R² = 0.9302
R² = 0.7171
L3-L2
y = -2E-10x6 + 5E-07x5 - 0.0005x4 + 0.3069x3 - 97.442x2 + 16366x - 1E+06
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y = -5E-10x6 + 1E-06x5 - 0.0014x4 + 0.8285x3 - 273.5x2 + 48109x - 4E+06
60 61
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R² = 0.8454
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Towards Design and Development of Isothermal Cloud Chamber for Seeding
2
Experiments in Tropics and Testing of Pyrotechnic Cartridge
3
Figures Only
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7 8 9 10 11
Fig1a Cloud Chamber – Front door is closed.
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12 13 14
1
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Fig.1(b)Left. Inside view of the cloud chamber. Right-top is the NaCl powder spray unit. It has fan inside for blowing the powder out of mesh. Right-middle is the NaCl nebulizer unit which produces spray of NaCl droplets for seeding. Powder spray unit and the nebulizer unit both are kept on the same platform as per the need of experiment. Right-bottom is the pyrotechnic cartridge burning stand under the canopy. Horizontal pipe holding it has the electric wire for triggering the fire. 15
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20
Air Filters of 1µm, 3 µm and 5 µm
N
Nebulizer
AC C E H HS HPG LED C LMD LR LS
Air Compressor Circulator Fan Evaporator Heater Humidity Sensor High Pressure Valve LED Camera Luxmeter Digital Display Luxmeter receiver Luxmeter Source
OL PTCH PG PRV S Ts VD VS VP
Outlet for Air Pyrotechnic Cartridge Holder Pressure Gauge Pressure Relief Valve Salt powder spry stand Temperature Sensor Video Display Screen Vacuum Sensor Vacuum Pump
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AF
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Fig. 2. Schematic diagram of Cloud Chamber.
3
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25 26 27
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Fig. 3 Extinction correction values1-f, as determined by Monte Carlo simulation (heavy lines)and light lines for water spheres and various pin-hole aperture sizes(as listed on the plot) as functions of particle diameter D. (By Korolev, et al. 2012)
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Fig.4 Single Stage refrigeration Unit line Diagram
29 30
34 35 36
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Temperature Chart 160 140
100 80 60 40 20 0 -25
-20
-15
38 39 40
47
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0
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44
-5
Figure 5: Graph showing best fit six order polynomial curve and trend line for Temperature (0C) at x-axis vs Lux meter reading difference at y-axis (L2-L1 in blue, L3-L2 in red, and L4-L3 in green)
41
43
-10
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Pressure Chart 160 140
100 80 60 40 20 0 550
500
450
49 50 51
53
59
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300
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Figure 6: Graph showing best fit six order polynomial curve and trend line for Pressure(mmHg) at x-axis vs Lux meter reading difference on y-axis (L2-L1 in blue, L3-L2 in red, and L4-L3 in green). At 00C, 0.0075006156130264 mmHg = 0.01 hPa.
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Figure A1 Perforated pyrotechnic cartridge. Case made up of PVC
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Figure-A2: Graph showing Nucleation and growth to precipitation by different pyrotechnic cartridge at 0 min, 5min, 15 min, and 30 min. All cartridge testing experiments were conducted at 98% RH and temperature -100C. Each cartridge got completely burnt after the nicrome trigger within 20-30 seconds. Graph show that the cloud takes about 30 minutes to come into a quasi-steady state equilibrium, and that as the number of nuclei continue to be ingested they coagulate. In some cases because of the method of their creation and resulting coating act as submersion nuclei, allowing cloud – aerosol interaction that yields a broadening of the droplet size distribution.
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Highlights 1.
A new Isothermal cloud Chamber is designed and fabricated based on optical scattering concept. It is first of its kind for testing the efficiency of seeding agents in simulated warm or cold cloud condition. Results obtained for optimum temperature range of efficiency for IN seeding; match fairly well, with
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preexisting results independently obtained after actual atmospheric seeding. 3.
Entire process of condensation growth and precipitation takes place only ≈ 30 minutes within the chamber.
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6th order polynomial successfully simulates the spontaneous condensation process for simultaneous
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Percentage Cartridge efficiency has been defined
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variation of pressure and temperature with very high coefficient of determination.
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