Microstructure of cirrus clouds observed by HYVIS

ATMOSPHERIC RESEARCH ELSEVIER

AtmosphericResearch 32 (1994) 115-124

Microstructure of cirrus clouds observed by HYVIS H. M i z u n o , T. M a t s u o , M. M u r a k a m i , Y. Y a m a d a Meteorological Research Institute, Tsukuba, Ibaraki 305, Japan (Received November 20, 1992; revisedand acceptedJuly 19, 1993)

Abstract In situ observations of cirrus clouds were carried out using a special sonde, the hydrometeor videosonde (HYVIS), at Tsukuba, Japan, in June 1989. The HYVIS provided direct images of cloud particles of 7 pm to 1 cm in size by radio. The HYVIS observations were made of three cirrostratus clouds extended northward portion from the surface warm and stationary fronts. The cloud base and cloud top were about 7 km ( - 2 0 °C) and 13 km( - 6 0 °C), respectively. They contained no cloud droplets and were composed of ice crystals of 10 pm to 1.5 mm in size. The concentrations of ice crystals were about l05 m -3. Most of the ice crystals were column and bullet types, providing the 22 ° halo. It is suggested that the ice crystals grew by deposition in a synoptic scale updraft region up to 10 cm s- J. The results provided an useful information about composition and structure of cirrus clouds.

I. Introduction It is well known that cirrus clouds are closely involved in the radiative energy balance in the atmosphere (e.g., Liou, 1986; Liou, 1992). They reflect solar radiation and also absorb infrared radiation emitted by the Earth's surface and lower clouds. Infrared radiation emitted by the Earth-atmosphere system is decreased by the presence of cirrus clouds. Furthermore, cirrus clouds cover about 20% of the globe (Barton, 1983). They are considered to have an important effect on climate. The optical properties of cirrus clouds are highly dependent on their microphysical properties such as types and sizes of ice crystals. For example, halos formed in cirrostratus are attributed to the refraction of the light in hexagonal ice crystals (e.g., Humphreys, 1964; Greenler, 1980). Information on the composi0169-8095/94/$07.00 © 1994 ElsevierScienceB.V. All rights reserved SSDIO169-8095(93)EO061-3

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tion and structure of cirrus clouds is needed for estimation of their optical and also radiative properties. Composition and structure of cirrus clouds are observed by two different methods: one remote sensing, the other in situ observations. Satellite, lidar and radar are remote sensing measurements. Satellite can observe cirrus clouds over global scale area (Curran and Wu, 1982; Barton, 1983). The advantage of lidar is continuous observation of vertical structure of clouds (Platt, 1973; Uchino et al., 1988; Imasu and Iwasaka, 1991; Sassen, 1991 ). However, remote sensing can not directly determine crystal types and size distribution of ice particles. The types and size distribution have been observed by aircraft observations (Braham and Spyers-Duran, 1967; Heymsfield and Knollenberg, 1972; Knollenberg, 1972; Heymsfield, 1975, 1986; Heymsfield et al., 1990). Although Knollenberg 2D-C probe has often been used in aircraft observations, it is well known that the measurements for small particle less than about 100/zm in size do not enough to discern phase and types of particles from its shadow image (Heymsfield and Baumgardner, 1985). In order to overcome these difficulties, recently Tanaka et al. (1989) and Murakami and Matsuo (1990) have developed an airborne video-microscope for measuring cloud particles (AVIOM-C) and a special sonde, the hydrometeor videosonde (HYVIS), for cloud and precipitation particles. The HYVIS can provide direct images ofhydrometeors from 7/2m to 1 cm with two TV cameras by radio, and observe a vertical distribution of hydrometeor as well as meteorological elements. With the HYVIS Mizuno and Murakami ( 1989 ), Matsuo et al. (1992) and Murakami et al. (1992a) observed successfully microphysical structures of winter monsoon snow clouds, and Murakami et al. (1992b) investigated warm-frontal clouds. Using the HYVIS, in situ observations of cirrus clouds were made in June 1989 at Tsukuba, Japan. The purpose of this paper is to present the results of the cirrus cloud observations and to describe the microstructure.

2. Synoptic condition The HYVIS observations were made of three cirrostratus clouds: one cirrostratus cloud extended northward portion from the surface stationary front on 22 June 1989, the other two clouds extended northeastward from the surface warm front on 30 June 1989. Here only results of a detailed case study for 22 June will be described, because this case was observed intensively by 3-hourly soundings over a 18-hour period. The other cases had a similar characteristics in microstructure. Fig. 1 shows a satellite picture around the Japanese Islands on the observation day. A surface stationary front (heavy line), Baiu front, is located about 300 km south of the site (filled triangle), Tsukuba, and a 20 kPa jet core (broken line) to the north of the site parallels the Baiu front. This situation indicates that there exists a frontal zone tilting toward the cold air with increasing height. A wide

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Fig. 1. Visible GMS-3 image at 1200LST 22 June 1989. Heavy line and broken line denote a surface stationary front (Baiu front) and 20 kPa jet core, respectively. A filled triangle represents an observation site. (Meteorological Satellite Center, JMA photo)

cloud band system in Fig. 1 is associated with the Baiu front overrunning to the north. The Baiu front moved slowly northward, and the cloud layer over the site changed from upper clouds at 0830 LST to middle cloud at 1130 LST. The HYVIS observation was carried out at 1105 LST in the course of the northward movement of the large scale system.

3. Microstructure

3.1. Sounding Fig. 2 shows profiles of temperature and humidity with respect to water observed with the HYVIS. From Fig. 2 cloud base was determined to be about 7 km ( - 20 ° C) and cloud top was estimated to reach the tropopause level at about 13 km ( - 60°C), although the measurement of humidity becomes unreliable as temperature decreases, especially below - 4 0 ° C. Below the cloud base air was very dry and air inside cloud layer was estimated to be almost ice-saturated (82% at - 2 0 ° C and 75% at - 3 0 ° C ) .

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HUMIDITY (%) 40 60 80 100 F---~T ~ I I~ r ! • ~ II05LST 22 -1150 " JUN 1989 4200 '\\\ TSUKUBA • ~'~

0 20 151~ ~ ~ 'h t ~ L~ v

/-

T

J•

T 5

j {

"

""-,a

\ J

-60

I

' ....

400 4S00 :

............

40

-20 0 TEMPERATURE (°¢)

20

Fig. 2. Temperature and humidity profiles for 1105LST 22 June 1989.

3.2. Types of cloud particles HYVIS has two TV images different in magnification: one close-up image for precipitation particles, the other microscope image for cloud particles. The sampiing volume per each image in this case is about 3 1 for the former and about 0.06 1 for the latter. HYVIS observation provided images of single ice crystals in the cloud layer. Cloud droplets and aggregates were not observed, although the collection efficiency of HYVIS for cloud droplets with diameter D ( < 130/zm) and for aggregates larger than 300 #m are determined to be 0.067D+0.14 and 0.77, respectively (Murakami and Matsuo, 1990 ). Fig. 3 shows images taken through a closeup and microscope TV cameras at 9.8 km ( - 34°C) in the middle of the cloud layer. The close-up image shows an ice crystal (340 #m in size) with a background of a portion of 22 ° halo and a balloon (dark circle in center). The microscope image shows a solid bullet (240/zm in length and 64 ~tm in width). The columnar crystal occurrence is consistent with the halo appearance, in accordance with the crystal habit expected from ice crystal diagram of Magono and Lee (1966). Most of ice particles in the cirrostratus were identified to be column or bullet types from the microscope images. Fig. 4 shows a vertical distribution of close-up images of the HYVIS showing a portion of halo. In Fig. 4 halos appeared in the layer between 8.5 km and 11.5 km. In that layer, column or bullet types were detected by the microscope images.

3.3. Size distribution Fig. 5 shows the vertical change in size distribution of ice crystals obtained from the micrographs. In order to decrease statistical sampling errors, size distribution in every 500 m in depth were calculated. The sampling volume for micro-

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119

CIRROSTRATUS 1125LST 22 JUN1989

8.5mm

I= I - -

1---

10 °

1.6mm

,-I -t

-34"C

9.8 km

,q

Fig. 3. Ice crystal images observed at 9.8 km M.S.L. ( - 34 ° C). The top image shows a ice crystal (340 # m in size), a portion o f 22 ° halo, and a balloon taken through a close-up TV camera. The b o t t o m shows a solid bullet taken through a microscope TV camera.

scope images in this data procedure is about 0.3 1 and for close-up images 15 1. Ice crystals are composed of about 10 #m to 240 #m in size in the upper and middle part of the cloud. The total concentrations are about 105 m - 3 and the number concentration generally decreases with increasing size. In the lower part of the cloud, the concentration decreases. From the close-up images, ice crystals up to 1.5 mm were found in the middle part of the cloud layer. The total concentration of ice crystals in close-up images were about 103 m-3 in the middle and upper part of the cloud layer, and decreased in the lower part. These are consistent to the results from microscope images. Considering absence of droplets and the vertical change in size distribution of ice crystals, it is inferred that the ice crystals in the cirrostratus grew by deposition as they fall.

H. Mizuno et al. /Atmospheric Research 32 (1994) 115-124

120

HYVIS 13

IMAGES

FOR C I R R O S T R A T U S TSUKUBA 1105LST 22 JUN 1989

12

11

,~10 E ,¢

"1"

V

-rm

O _d

9

LL! "1-

8

7

6

Fig. 4. Vertical distribution of HYVIS images showing 22 ° halos for 1105LST 22 June 1989.

H. Mizuno et al. / Atmospheric Research 32 (1994) 115-124

121

1105LST 22 JUN 1989 15~! ~ i -i --[---- -60 -40v

HALO

--30 !

I O 5-19

~-20

~< rr IJJ

4qO

~

!

I o o_79 i 0

0

_1 I 100 200 SIZE (IJm)

I 300

i

10

120

Fig. 5. Vertical change in size distribution of ice crystals. The number concentration of ice crystals in each 500 m layer is indicated.

jWc

WANL

"-6o

--20 ~ UA

--tO ~ i 1105LST 22 I JUN 1989 L TSUKUBA 0 ~ -30

-0

tlA i.--

- ~0

~ ±

L ~_ ! L2o 50 100 VERTICAL VELOCITY (cmls)

Fig. 6. Vertical velocity (WANL) and critical vertical velocity (We) are indicated. WANL is estimated from the isentropic method. Wc is calculated using the data of ice crystal concentration observed on the assumption that ice crystals grow by deposition in water saturated condition in the absence of cloud droplets,

3.4. Vertical velocity

Estimation of vertical velocity profile was made using the isentropic method according to Starr and Wylie (1990). Although it should be noted that this method has some errors to the vertical velocity, the updrafts up to 10 cm s-1 were analyzed in the region between the cloud base and 12 km level ( WANLin Fig. 6 ). In order to examine the relationship between the updraft profile and the ob-

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H. Mizuno et al. / Atmospheric Research 32 (1994) 115-124

served microstructure, a critical vertical velocity (Wc) was defined and was calculated according to Jiusto ( 1971 ). It was defined as the vertical velocity which allows all ice crystals to grow by deposition in water-saturated without producing any droplets. If the analyzed vertical velocity (WANL) is higher than Wo cloud droplets will be expected. Since WANLis lower than Wc through the middle and upper part of the cloud, it is considered that no cloud droplets are produced and ice crystals grow by depositional process. These are consistent with the observed microstructure.

4. Conclusions Cirrostratus clouds extending northward from a surface stationary front and warm front were observed by the HYVIS. The microstructure of the cirrostratus clouds is schematically represented in Fig. 7. The main results are summarized as follows: ( 1 ) Updraft up to 10 cm s- ~associated with a large-scale frontal overrunning was analyzed in the clouds. (2) The clouds had no cloud droplets included and were composed of single ice crystals of about 10 a m to 1.5 m m which grew by deposition. ( 3 ) The dominant types of ice crystals were column and bullet types and were consistent with a 22 ° halo in the middle part of the clouds. (4) In the upper and middle parts of the clouds, the total concentrations were about 105 m -3 and the number concentration generally decreased with size. The largest ice crystals were found in the middle part. (5) In the lower part of the clouds, the concentration of ice crystals decreased. These results provide useful information on the composition and structure of cirrus clouds. CIRROSTRATUS (ll05LST 22 JUN 1989, TSUKUBA) 13km ~

~1

-10pm]

-- -600C

-105/m 3 / / I DEPOSITION / ":" i

~ ~10 cm/s

~

-! m m I 1

HALO -

~ ~O

--

-20

ICE CRYSTALS

NO DROPLETS 7k

m

~

Fig. 7. Schematicdrawingof verticalstructurein the cirrostratusclouds.

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Acknowledgements This work was done as a part of the WCRP/MRI program entitled "the Field Experiments and Theoretical Modeling of Cloud-Radiation Processes" (FY19871990 ). We would like to thank all the colleagues who contributed to this experiment. We would also like to acknowledge the contribution of the Aerological Observatory in providing special rawinsonde data. The computations were made with the HITAC M280D Computer Systems of the MRI. References Barton, I.J., 1983. Upper level cloud climatology from an orbiting satellite. J. Atmos. Sci., 40: 435447. Braham, R.R. and Spyers-Duran, P., 1967. Survival of cirrus crystals in clear air. J. Atmos. Meteorol., 6: 1053-1061. Curran, R.J. and Wu, M.L.C., 1982. Skylab near-infrared observations of clouds indicating supercooled liquid water droplets. J. Atmos. Sci., 39: 635-647. Greenler, R., 1980. Rainbows, Halos, and Glories. Cambridge University Press, New York, pp. 2364. Heymsfield, A.J. and Knollenberg, R.G., 1972. Properties of cirrus generating cells. J. Atmos. Sci., 29: 1358-1366. Heymsfield, A.J., 1975. Cirrus uncinus generating cells and the evolution of cirriform clouds, part I: Aircraft observations of the growth of the ice phase. J. Atmos. Sci., 32: 799-808. Heymsfleld, A.J. and Baumgardner, D., 1985. Summary of a workshop on proceeding 2-D probe data. Bull. Am. Meteorol. Soc., 66: 437-440. Heymsfield, A.J., 1986. Ice particles observed in a cirriform clouds at - 8 3 ° C and implications for polar stratospheric clouds. J. Atmos. Sci., 43:851-855. Heymsfield, A.J., Miller, K.M. and Spinhirne, J.D., 1990. The 27-28 October 1986 FIRE IFO cirrus case study: Cloud microstructure. Mon. Weather Rev., 118:2313-2328. Humphreys, W.J., 1964. Physics of the Air. 3rd. ed. Dover, New York, pp. 501-536. Imasu, R. and Iwasaka, Y., 1991. Characteristics of cirrus clouds observed by laser radar (lidar) during the spring of 1987 and the winter of 1987/88. J. Meteorol. Soc. Jpn., 69:401-411. Jiusto, J.E., 1971. Crystal development and glaciation of a supercooled cloud. J. Rech. Atmos., 5: 6985. Knollenberg, R.G., 1972. Measurements of the growth of the ice budget in a persisting contrail. J. Atmos. Sci., 29: 1367-1374. Liou, K.N., 1986. Influence of cirrus clouds on weather and climate processes: A global perspective. Mon. Weather Rev., 114:1167-1199. Liou, K.N., 1992. Radiation and Cloud Processes in the Atmosphere. Oxford Univ. Press, 487 pp. Magono, C. and Lee, C.W, 1966. Meteorological classification of natural snow crystals. J. Fac. Sci., Hokkaido Univ., Ser. VII, 2: 321-335. Matsuo, T., Murakami, M., Mizuno, H. and Yamada, Y., 1992. Requisites for graupel formation in Japan Sea snow clouds. In: Proc. 1 lth Int. Conf. Clouds and Precipitation. Montreal, Canada, pp. 252-255. Mizuno, H. and Murakami, M., 1989. Microstructure of winter monsoon snow clouds over the Sea of Japan observed with HYVIS. WMO/TD, 269: 69-72. Murakami, M. and Matsuo, T., 1990. Development of the Hydrometeor Videosonde. J. Atmos. Ocean. Tech., 7: 613-620. Murakami, M., Matsuo, T., Mizuno, H. and Yamada, Y., 1992a. Microphysical structures of convective snow clouds over the Sea of Japan. In: Proc. 1 lth Int. Conf. Clouds and Precipitation. Montreal, Canada, pp. 207-210.

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Murakami, M., Matsuo, T., Mizuno, H. and Yamada, Y., 1992b. Microphysical structures of warmfrontal clouds.--The 20 June 1987 case study--. J. Meteorol. Soc. Jpn., 70: 877-895. Platt, C.M.R., 1973. Lidar and radiometric observations of cirrus clouds. J. Atmos. Sci., 30:11911204. Sassen, K., 1991. The polarization lidar technique for cloud research: A review and current assesment. Bull. Am. Meteorol. Soc., 72: 1848-1866. Starr, D. O'C. and Wylie, D.P., 1990. The 27-28 October 1986 FIRE cirrus case study: Meteorology and clouds. Mon. Weather Rev., 118: 2259-2287. Tanaka, T., Matsuo, T, Okada, K., Ichimura, I., lchikawa, S. and Tokuda, A., 1989. An airborne video-microscope for measuring cloud particles. Atmos. Res., 24:71-80. Uchino. O., Tabata, I., Kai, K. and Okada, Y., 1988. Polarization properties of middle and high level clouds observed by lidar. J. Meteorol. Soc. Jpn., 66:607-616.