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Field measurements of the effects of cloud condensation nuclei on cloud microphysics in various environments
J. Aemsol Sci. Vol. 29, Suppl. 1, pp.S565-M66.1998 0 1998 Published by Elsevier Science Ltd. All rights reserved Printed in Great Britain OOZI-8502/98$19.OO+O.OO
Pergamon
FIELD MEASUREMENTS OF THE EFFECTS OF CLOUD CONDENSATION NUCLEI ON CLOUD MICROPHYSICS IN VARIOUS ENVIRONMENTS J. G. HUDSON, S.S. YUM and Y. XIE Desert Research Institute, P.O. Box 60220, Reno, NV 89506-0220, USA Airborne cloud condensation nuclei (CCN) spectral measurements (Hudson 1989) were made in several field projects (Southern Ocean Cloud Experiment-SOCEX, Aerosol Characterization Experiment-ACE, Small Cumulus Microphysics Study-SCMS). Table 1 shows project averages of all flights (5 to 15 of 2 to 10 hours duration). The CN (total particles) and CCN were measured in the boundary layer near cloud base. Cloud droplet concentrations (NC) were obtained with a forward scattering spectrometer probe (FSSP-2 to 50 urn diameter). MD refers to the mean diameter of the cloud droplet spectrum. Ld is the liquid water content of the drizzle drops (50-620 urn diameter--260X probe). S,g was determined by matching N, with the appropriate supersaturation (S) of the CCN spectrum (Hudson 1984). Table 1. Project Average CCN and Cloud Microphysical Measurements for 4 projects. 1 SOCEXl
CN (cm”) CCN@l% (cm”) [email protected]% (cm”) s.ff (%> N, (cm-3)_FSSP MD(um)_FSSP Ld (mg m”) 260X
Winter 227 36 7 0.93 28 17.1 122
SOCEX2 Summer 457 201 72 0.19 70 13.9 61
ACE- 1 Summer 372 200 72 0.12 56 13.7 34
SCMS maritime 1650 330 189 0.11 117 15.9 4
SCMS continental 2567 1010 454 0.17 256 10.7 1
The CCN, MD, and N, progression seems to uphold the first Twomey effect (indirect aerosol effect)--higher CCN concentrations caused higher N, and smaller MD (Twomey 1977). There is support for the second Twomey effect--the inhibition of drizzle by higher CCN and N, (e.g., Albrecht 1989). The cleanest air ( wintertime Southern Hemisphere-SOCEX-1) also produced the highest !& which seems to uphold the suppression of S by higher CCN concentrations (e.g., Twomey 1959). Less drizzle in SCMS was probably due to smaller sizes and shorter lifetimes of the clouds rather than to the higher CCN concentrations. Nevertheless, the relative difference in drizzle between the two SOCEX and SCMS phases is probably supportive of drizzle inhibition. Note the extraordinary similarities for all parameters between the two Southern Hemisphere summertime projects (SOCEX2 and ACE-l). Figure 1 shows the relationship between CCN and N, for both phases of SOCEX. Each data point is the average for each flight. Figure 2 shows the predictions of N, vs. measurements of N,. The predictions were from a droplet growth model (Robinson 1984) using the fI.111 CCN spectra below cloud and in-cloud updraft velocities. As in Fig. 1 these data points are averages for each flight.
SSf56
Abstracts
of the 5th International
500
Aerosol Conference 150
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400 -
Winter Summer
1998
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Winter
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Summer
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100 sl=99.95+% 0
I 0
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I
I
100
150
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NC (cmm3)
30
60
90
120
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NC (cm9)
Fig. 1. Comparisons of averages for entire flights of CCN (at 1% S) and cloud droplet concentrations during SOCEX.
Fig. 2. Comparisons of predicted vs. measured droplet concentrations for SOCEX. As in Fig. 1 these are flight averages.
ACKNOWLEDGEMENTS This work was supported by NASA grant # NAGW-3753 and NSF grants ATM9419263 and ATM-9422170. Jorgen Jensen and Reinout Boers provided the microphysical data from the CSIRO F-27 in SOCEX. NCAR-RAF provided the microphysical data from ACE-l and SCMS. REFERENCES Albrecht, B.A., (1984) Aerosols, cloud microphysics and fractional cloudiness, Science, 245, 1227-1230. Hudson, J.G., (1984) CCN measurements within clouds, .I Climat. Appl. Meteor., 23, 42-5 1. Hudson, J.G., (1989) An instantaneous CCN spectrometer, .J. Atmos. & Ocean. Tech., 6, 1055-1065. Robinson, N.F., (1984) The efficient numerical calculation of condensational cloud drop growth, J. Atmos. Sci., 41, 697-700. Twomey, S., (1959) The supersaturation in natural clouds and the variation of cloud droplet concentration, Geofis. pura appl. 43,243-249. Twomey, S., (1977) The influence of pollution on the shortwave albedo of clouds, J. Atmos. Sci., 34, 1149-l 152.
Pergamon
FIELD MEASUREMENTS OF THE EFFECTS OF CLOUD CONDENSATION NUCLEI ON CLOUD MICROPHYSICS IN VARIOUS ENVIRONMENTS J. G. HUDSON, S.S. YUM and Y. XIE Desert Research Institute, P.O. Box 60220, Reno, NV 89506-0220, USA Airborne cloud condensation nuclei (CCN) spectral measurements (Hudson 1989) were made in several field projects (Southern Ocean Cloud Experiment-SOCEX, Aerosol Characterization Experiment-ACE, Small Cumulus Microphysics Study-SCMS). Table 1 shows project averages of all flights (5 to 15 of 2 to 10 hours duration). The CN (total particles) and CCN were measured in the boundary layer near cloud base. Cloud droplet concentrations (NC) were obtained with a forward scattering spectrometer probe (FSSP-2 to 50 urn diameter). MD refers to the mean diameter of the cloud droplet spectrum. Ld is the liquid water content of the drizzle drops (50-620 urn diameter--260X probe). S,g was determined by matching N, with the appropriate supersaturation (S) of the CCN spectrum (Hudson 1984). Table 1. Project Average CCN and Cloud Microphysical Measurements for 4 projects. 1 SOCEXl
CN (cm”) CCN@l% (cm”) [email protected]% (cm”) s.ff (%> N, (cm-3)_FSSP MD(um)_FSSP Ld (mg m”) 260X
Winter 227 36 7 0.93 28 17.1 122
SOCEX2 Summer 457 201 72 0.19 70 13.9 61
ACE- 1 Summer 372 200 72 0.12 56 13.7 34
SCMS maritime 1650 330 189 0.11 117 15.9 4
SCMS continental 2567 1010 454 0.17 256 10.7 1
The CCN, MD, and N, progression seems to uphold the first Twomey effect (indirect aerosol effect)--higher CCN concentrations caused higher N, and smaller MD (Twomey 1977). There is support for the second Twomey effect--the inhibition of drizzle by higher CCN and N, (e.g., Albrecht 1989). The cleanest air ( wintertime Southern Hemisphere-SOCEX-1) also produced the highest !& which seems to uphold the suppression of S by higher CCN concentrations (e.g., Twomey 1959). Less drizzle in SCMS was probably due to smaller sizes and shorter lifetimes of the clouds rather than to the higher CCN concentrations. Nevertheless, the relative difference in drizzle between the two SOCEX and SCMS phases is probably supportive of drizzle inhibition. Note the extraordinary similarities for all parameters between the two Southern Hemisphere summertime projects (SOCEX2 and ACE-l). Figure 1 shows the relationship between CCN and N, for both phases of SOCEX. Each data point is the average for each flight. Figure 2 shows the predictions of N, vs. measurements of N,. The predictions were from a droplet growth model (Robinson 1984) using the fI.111 CCN spectra below cloud and in-cloud updraft velocities. As in Fig. 1 these data points are averages for each flight.
SSf56
Abstracts
of the 5th International
500
Aerosol Conference 150
0 0
400 -
Winter Summer
1998
0
Winter
0
Summer
300
200
60
100 sl=99.95+% 0
I 0
50
I
I
100
150
200
0
NC (cmm3)
30
60
90
120
150
NC (cm9)
Fig. 1. Comparisons of averages for entire flights of CCN (at 1% S) and cloud droplet concentrations during SOCEX.
Fig. 2. Comparisons of predicted vs. measured droplet concentrations for SOCEX. As in Fig. 1 these are flight averages.
ACKNOWLEDGEMENTS This work was supported by NASA grant # NAGW-3753 and NSF grants ATM9419263 and ATM-9422170. Jorgen Jensen and Reinout Boers provided the microphysical data from the CSIRO F-27 in SOCEX. NCAR-RAF provided the microphysical data from ACE-l and SCMS. REFERENCES Albrecht, B.A., (1984) Aerosols, cloud microphysics and fractional cloudiness, Science, 245, 1227-1230. Hudson, J.G., (1984) CCN measurements within clouds, .I Climat. Appl. Meteor., 23, 42-5 1. Hudson, J.G., (1989) An instantaneous CCN spectrometer, .J. Atmos. & Ocean. Tech., 6, 1055-1065. Robinson, N.F., (1984) The efficient numerical calculation of condensational cloud drop growth, J. Atmos. Sci., 41, 697-700. Twomey, S., (1959) The supersaturation in natural clouds and the variation of cloud droplet concentration, Geofis. pura appl. 43,243-249. Twomey, S., (1977) The influence of pollution on the shortwave albedo of clouds, J. Atmos. Sci., 34, 1149-l 152.