Microphysical Effects of Cloud Seeding in Supercooled Stratiform Clouds Observed from NOAA Satellite

Transcription

1 224 ACTA METEOROLOGICA SINICA VOL.21 Microphysical Effects of Cloud Seeding in Supercooled Stratiform Clouds Observed from NOAA Satellite DAI Jin 1 ( ), YU Xing 1 ( ), Daniel ROSENFELD 2, and XU Xiaohong 1 ( ) 1 Meteorological Institute of Shaanxi Province, Xi an , China 2 Institute of Earth Sciences, the Hebrew University of Jerusalem, Israel (Received March 3, 2007) ABSTRACT Based on the satellite retrieval methodology, the spectral characteristics and cloud microphysical properties were analyzed that included brightness temperatures of Channels 4 and 5, and their brightness temperature difference (BTD), the particle effective radius of seeded cloud track caused by an operational cloud seeding and the microphysical effects of cloud seeding were revealed by the comparisons of their differences inside and outside the seeded track. The cloud track was actually a cloud channel reaching 1.5-km deep and 14-km wide lasting for more than 80 min. The effective radius of ambient clouds was µm, while that within the cloud track ranged from 15 to 26 µm. The ambient clouds were composed of supercooled droplets, and the composition of the cloud within the seeding track was ice. With respect to the rather stable reflectance of two ambient sides around the track, the visible spectral reflectance in the cloud track varied at least 10%, and reached a maximum of 35%, the reflectance of 3.7 µm in the seeded track relatively decreased at least 10%. As cloud seeding advanced, the width and depth were gradually increased. Simultaneously the cloud top temperature within the track became progressively warmer with respect to the ambient clouds, and the maximum temperature differences reached 4.2 and 3.9 C at the first seeding position for Channels 4 and 5. In addition, the BTD in the track also increased steadily to a maximum of 1.4 C, compared with C of the ambient clouds. The evidence that the seeded cloud became thinner comes from the visible image showing a channel, the warming of the cloud tops, and the increase of BTD in the seeded track. The seeded cloud became thinner mainly because the cloud top descended and it lost water to precipitation throughout its depth. For this cloud seeding case, the glaciation became apparent at cloud tops about 22 min after seeding. The formation of a cloud track in the supercooled stratiform clouds was mainly because that the seeded cloud volume glaciated into ice hydrometeors that precipitated and so lowered cloud top height. A thin line of new water clouds formed in the middle of the seeded track between 38 and 63 min after seeding, probably as a result of rising motion induced by the released latent heat of freezing. These clouds disappeared in the earlier segments of the seeded track, which suggested that the maturation of the seeding track was associated with its narrowing and eventual dissipation due to expansion of the tops of the ambient clouds from the sides inward. Key words: cloud seeding effect, cloud track, satellite retrieval, microphysical property, spectral characteristics 1. Introduction The first launch of TIROS in 1960 in the United States opened a new era of observing the atmosphere from the space. The satellite technology and development of satellite retrieval methodologies provide an observation platform to further learn and understand clouds. Compared with the surface observation, radar, and aircraft with microphysical instruments, the satellite can supply more information of clouds and precipitation on various temporal and spatial scales. At the end of 1980, when the satellite observed ship tracks through thin marine stratocumulus clouds over the Pacific Ocean, it brought our awareness to the coalescence-suppressing effects of pollution aerosols from the stacks of ships, which provides a vivid demonstration of the profound effects of anthropogenic aerosols on the radiative properties and microphysical structure of maritime stratocumulus clouds (Coakley et al., 1987; Radke et al., 1989; Albrecht, 1989). With the increase of sensor channels and progress of retrieval methodologies, more and more microphysical Supported jointly by the National Natural Science Foundation of China under Grant No and the Chinese Ministry of Science and Technology (Grant 2005DIB3J099). Corresponding author: daijohn@msn.com.

2 NO.2 DAI Jin, YU Xing, Daniel ROSENFELD and XU Xiaohong 225 properties of clouds can be obtained from the visible, far-infrared, and mid-infrared wavebands, which typically include the temperature, height, effective particle radius, particle phase of cloud top, and the cloud optical depth. The microphysical properties of clouds can reflect the precipitation forming process. Rosenfeld and Lensky (1998) proposed a satellite retrieval method to infer the relation between the vertical evolution of cloud microstructure and precipitation forming processes in convective clouds, based on the variation of cloud particle effective radius with temperature. This methodology was applied to get a insight into precipitation suppression by smoke from forest fires (Rosenfeld, 1999) and by urban and industrial air pollution (Rosenfeld, 2000), and the way by which large salt aerosols can restore the precipitation (Rosenfeld et al., 2002; Rudich et al., 2002). However, in China, the satellite retrieval methodologies were mainly used to analyze microphysical properties of clouds (Liu et al., 1998, 1999; Zhang and Xu, 2004, Zhang and Zhang et al., 2004; Zhang and Li et al., 2004) and rarely to obtain the information of precipitation forming process. The effects of anthropogenic or natural aerosols on precipitation have been observed many times by satellites that can be considered as the inadvertent cloud seeding. However, besides two previous probable advertent glaciogenic seeding signatures in convective clouds (Woodley et al., 2000; Rosenfeld and Woodley, 2003), there are few reports concerning the effects of advertent seeding clouds observed by satellites in the past. Fortunately, just after an operation of cloud seeding for precipitation enhancement by aircraft was carried out from 1415 to 1549 BT (Beijing Time) 14 March 2000 at the middle part of Shaanxi Province, China, the NOAA-14 satellite imagery was received at 1535 BT. A vivid cloud track appeared on the satellite imagery. By the use of a three-dimensional numerical model of transport and diffusion of seeding material, Yu et al. (2005) demonstrated that the cloud track detected by NOAA satellite was the direct physical evidence of cloud seeding near cloud top. In this paper the satellite retrieval methodology was used to analyze quantitatively the satellite data and to obtain further physical insight to the seeding effects. 2. Cloud seeding operation At 1415 BT 14 March 2000, a seeding operation for precipitation enhancement was carried out by the Center of Weather Modification of Shaanxi Province, when Shaanxi Province was influenced by a frontal weather system. The altostratus (As) and altocumulus (Ac) were main cloud types, and sparse rain was observed on the surface over this area. The aircraft An-26 with an airborne silver iodide solution burner was used in the operation of weather modification, and the average flight speed was 360 km h 1. The seeding duration was 94 min, and consumed 1200 g AgI. The times and coordinates of the seeding flight are given in Table 1. The aircraft ascended to the altitude of 4000 m while circling near airport, point O. The seeding operation started from turning point A, passed to turning points B, C, D, E, F, G, H, and I, and finished in point J. The seeding height was 4.35 km above sea level, where temperature was about 10.0 C. The height of the cloud base was km. Table 1. Operational report of cloud seeding (the initial seeding at 1415 BT and the satellite overpassing at 1535 BT) Seeding time (BT) Before satellite passage (min) Turning points ( N, E) O(34 24, ) A(34 18, ) B(34 24, ) C(34 15, ) D(34 41, ) E(34 31, ) F(34 54, ) G(34 21, ) H(33 38, ) I (33 19, )

3 226 ACTA METEOROLOGICA SINICA VOL.21 The cloud top height ranged from 4.5 to 5.3 km, where temperature was from 13.0 to 17.0 C. 3. Synoptic situation On the Eurasian synoptic map of 500 hpa at 2000 BT 14 March 2000, the middle and high latitudes were controlled by two troughs and one ridge situated near 80 E. The shortwave trough at the front of ridge slid continuously, and there existed an obvious shortwave trough near 110 E, where cold advection was located at the rear part of the trough with a weak uplift (Fig. 1a). On the corresponding surface synoptic map, there was a cold high pressure centered at 50 N, 110 E, and in front of it there was a low pressure centered at 33 N, 95 E. A cold front extended southwestward from the center of low pressure along the edge of high pressure, and swept over the seeding area (Fig.1b). Theoretically, the cold air wedges the base of warm air, which climbs along the front during the movement of front, and the warm air over the front ascends, while the cold air descends, which would cause the cloud system and precipitation to be behind the front, and the clouds from far would be Ac, Ns, As, Cs, and Ci. The observed clouds were low and medium ones including Ci, Ac, Ns, and As. A light precipitation from rain to snow was observed on the surface. 4. Retrieved cloud microphysical properties NOAA-14 satellite carries AVHRR-2 probe with 5 Channels, whose sub-satellite resolution is 1.1 km. Channel 1 centered at 0.6 µm is located at visible waveband, gives the reflectance of target to the sun, and can also be used to retrieve the optical depth of aerosols. Channel 2 centered at 0.9 µm is located at near-infrared waveband. Channel 3 centered at 3.7 µm is located at mid-infrared waveband, whose receiving radiation is composed of long-wave and reflecting one. The reflectance at this waveband depends on the size of cloud particle. Channels 4 and 5 are located at far-infrared waveband, centered at 10.8 and 12.0 µm, respectively, and receive long-wave radiation. After the imagery was rectified, it was synthesized from Channels 1, 2, and 4 with blue, green, and red (RGB) colors, respectively (Fig.2). The turning points A, B, C, D, E, F and G were corresponding to the seeding points A, B, C, D, E, F, and G, and the turning point matched with seeding turning point I could not be found on the image. According to the multi-spectral cloud classification scheme proposed by Rosenfeld and Leskey (1998), the clouds north to point F appearing in heavy red suggest that they are deep precipitating clouds (precipitation not necessarily reaching the ground), whose particles are larger, and the temperature of the cloud top is lower. The yellow indicates rather deep supercooled water clouds, and the green rather thin supercooled water clouds or the clouds composed of small ice particles, typically Ac or As. The seeding track appears conspicuously in red, imbedded in the ambient supercooled stratiform clouds in yellow and orange colors. The initial seeding was at 1415 BT, and the satellite overpassed this area at 1535 BT. The aircraft seeded point A 80 min before the satellite overpass time. The seeding track became younger from points A to H. The seeding aircraft passed through point H 14 min before that satellite overpassed. The cloud seeding flight time from A to H lasted for 66 min. In order to compare the properties of seeded track in different stages, 10 cross sections are chosen and marked with numbers 1 to 10 in Fig.2. Figure 3 displays the information of the individual AVHRR channels and some additional fields produced by them. In order to better understand the threedimensional cloud structure, the clouds are treated with a background of 12.0-µm brightness temperature. It is selected because the clouds have greater emissivity at this wavelength compared with 10.8 µm. With less water vapor above cloud tops as is the case here the 12.0-µm brightness temperature is closer to the actual cloud top temperature than that at 10.8 µm. Figures 3a and b show the 3-D microstructure and temperature of the cloud top. The color composite image (Figs.2 and 3a) highlights the cloud top microstructure and shows the sharp contrast between the flat-top supercooled stratiform clouds and the glaciated clouds in the seeded track, and the seeded track from C to A has been partly obstructed by the surrounding clouds.

4 NO.2 DAI Jin, YU Xing, Daniel ROSENFELD and XU Xiaohong 227

5 228 ACTA METEOROLOGICA SINICA VOL.21

6 NO.2 DAI Jin, YU Xing, Daniel ROSENFELD and XU Xiaohong 229 The cloud top temperature is generally cold in the north and a little warmer in the south as shown in Fig.3b, where the bluer color indicates the lower temperature, and in the seeding area, the temperature in the east is a little lower than that in the west. On the visible image (Fig.3c), there exists a shadow around the seeding track, which indicates the seeding appears to have produced a channel in the cloud tops. The channel is also visible in Fig.3b. Using the length of the shadows for calculating the depth of the channel, its depth is about 700 m at cross section 9 (see markings in Fig.2), and deepens to about 1300 m at cross section 7, remains about this depth to cross section 5 and deepens to about 1500 m at cross section 2. Figure 3d shows the brightness temperature difference (BTD) between Channels 4 and 5, where larger values are brighter and indicate thinner clouds. Apparently, the seeding track in the BTD image is less obscured by thin stratiform clouds above it. The seeded track can be seen under higher thin supercooled cloud near point F. The seeding track becomes wider all the way to point A in the BTD image. This suggests that the narrowing seeding track in the visible image (Figs.2, 3a, and 3b) is due to spreading of the preexisting water clouds from the sides and obstructing above the channel of the seeding tracks. This is evident visually in Fig.3a. The reflectance of 3.7 µm is illustrated in Fig.3e. The characteristics of reflectance in the seeding track differ greatly from those of ambient clouds. The dark of the seeding track indicates that the cloud droplets are larger or the cloud is composed of ice. This is because that ice absorbs strongly, twice as much as water at 3.7 µm. Figure 3f presents the retrieved effective radius (R e ) of cloud top particles, where the larger the R e, the brighter the clouds. 5. Comparison of microphysical properties inside and outside cloud track In order to fully analyze the seeding effects produced by cloud seeding, the spectral characteristics of Channels 1 and 3, the brightness temperatures of Channels 4 and 5, and the effective radii are presented in Fig.4 for the 10 cross sections, which stand for the different stages of seeded track. 5.1 Visible spectral reflectance The visible spectral reflectance of 0.6-µm waveband (A1, black lines in Fig.4) in the seeded track varies at least 10%, compared with that of two ambient sides around the track. From cross sections 10 to 7, the visible reflectances around the track are about 97%, but those in the track vary rarely in cross section 10 due to seeding just finishing, and about 10%, 15%, and 20% in cross sections 9, 8, and 7, respectively. The variation of visible reflectance in the track approaches and exceeds 20% for cross sections 6 and 5, on the basic of 90% reflectance for surrounding. With the seeding progress, the reflectances of ambient clouds decrease to 85%, 80%, 80%, and 75% for cross sections 4, 3, 2, and 1, respectively, on the contrast, the variation of reflectances in the track of corresponding cross sections change by about 10%, 10%, 35%, and 10%, respectively µm spectral reflectance For the same cross section, the reflectance of 3.7- µm waveband (A3, green lines in Fig.4) in the seeded track relatively decreases at least 10%, with respect to the rather stable reflectance of the two ambient sides around the track. For cross sections 10, 9, and 7, the 3.7-µm reflectances around the track are about 23%, but in the track ranging from 3% to 5%, although the absolute variation amplitudes are not so large, the relative variations are about 10%-20%. In cross sections 5 and 4, the reflectance is about 30% for the ambient clouds, and reduces to 20% in the cloud track, and the relative decrement exceeds 30%. The reflectances of clouds around track range 35%-38% from cross sections 3 to 1, but decrease at least by 15% in the track, and produce a relative decrement over 30%. In the track of cross sections 8, 6, and 1, the local increase of reflectance is due to the water there, which can also be seen from the decreasing effective diameters (D eff, the red line with circle in Fig.4). 5.3 The effective radius of cloud top particles The ambient clouds have the particle effective

7 230 ACTA METEOROLOGICA SINICA VOL.21 radius (R e ) of µm. R e increases and reaches a maximum of 26 µm within the track. It is about 19 µm in cross section 10, and exceeds 15 µm and reaches about 24 µm in cross sections 9 and 7. For cross sections 8 and 6, R e increases to 15 and 20 µm first, and then declines to 12 and 15 µm, respectively, due to the water in the seeded track. For cross sections 5 and 4, R e increases from 10 µm to about 20 µm, and ranges from 17 to 23, 17 to 20, and 17 to 26 µm, respectively, for cross sections 3, 2, and 1. The strong absorption of the solar reflectance component of 3.7 µm (Fig.3e) resulting in a large indicated effective radius of cloud top particle (Fig.3f) indicates that the composition of the cloud within the seeding track is ice. The typical size of ice particles that form in mixed phase clouds is much larger than 10 to 15 µm. Therefore, this combination of relatively small effective radius and low temperatures indicates that the ambient clouds are composed of supercooled droplets, possibly with low concentrations of ice particles. This suggests that the seeded cloud volume glaciates into ice, and then grows up to form precipitation and so lower cloud top height. 5.4 The brightness temperature of cloud top The temperature difference between the seeded track and ambient clouds increases with the progress of cloud seeding. Tables 2 and 3 list the temperature difference between them for satellite Channels 4 and 5. For Channel 4 (Table 2), the differences are continuously increased, and the track becomes progressively warmer with respect to the ambient cloud by 0.3, 1.0, 1.1, 1.7, and 1.5 C from cross sections 10 to 6, respectively. This trend of cloud top warming in the seeded track continues with its increasing age to a difference exceeding 2 C from cross sections 5 to 1 and reaches a maximum 4.2 C in cross section 1. For Channel 5 (Table 3), the trend of cloud top warming in the seeded track is similar to that for Channel 4. The differences are 0.3, 0.5, 0.6, 1.1, 0.8, and 1.2 C with respect to the ambient cloud from cross sections 10 to 5, exceed 2 C for cross sections 4, 3, and 2, and reach 3.9 C for cross section 1. Table 4 lists BTD between Channels 4 and 5. The BTD of ambient clouds are C, except for cross section 1, but the BTD within the track increases steadily from 0.7 C in cross sections 9 and 8 to maximum 1.4 C in cross sections 3 and 2, and in the track it also can reveal the decreased cloud thickness. The BTD is near zero for opaque clouds with cold tops. However, when the clouds become sufficiently thin or lose their water, the upwelling radiation from the warmer objects below the clouds would penetrate them and increase the brightness temperature, which is measured by the satellite instruments. Because 10.8 µm is more transparent to the thermal radiation than 12.0-µm channel, it will appear as having larger brightness temperature, so that the BTD would increase for less opaque clouds and for greater thermal contrast with the underlying surface (Inoue, 1989). The BTD of the ambient clouds is K, indicating that they are quite opaque and thick. The BTD within the seeded track decreases with some delay after the glaciation, showing no decrease in the newly glaciated track in cross section 10. At cross section 9 the BTD already increases to 0.7 K and keeps increasing gradually to 1.4 K in cross sections 2 and The width of seeded cloud track Table 5 displays the widths of seeded track for 10 cross sections. The newly glaciated track in cross sections 10 and 9 is not very wide. The widths of track increase with the seeding progress, reach 14 km in cross section 5, and fluctuate around 10 km from cross sections 4 to 1. Combined the depth of cloud track, it is actually a channel with width up to 14 km and depth up to 1.5 km. Table 2. Brightness temperatures and the differences between ambient cloud and cloud track for 10 cross sections in Channel 4 ( C) Cross section Cloud track Ambient clouds Difference

8 NO.2 DAI Jin, YU Xing, Daniel ROSENFELD and XU Xiaohong 231 Table 3. Brightness temperatures and the differences between ambient cloud and cloud track for 10 cross sections in Channel 5 ( C) Cross section Cloud track Ambient clouds Difference Table 4. Brightness temperature difference (BTD) between Channels 4 and 5 for 10 cross sections ( C) Cross section BTD within track BTD around track Table 5. Widths of the seeded track for 10 cross sections (km) Cross section Width Physical interpretation of cloud seeding Multi-spectral analyses of NOAA/AVHRR satellite data clearly reveal the structural and microphysical properties in the seeded track within supercooled stratiform clouds, and evidently document the differences and changes outside and inside seeded track, which are induced by an operational cloud seeding. The cloud seeding produces a channel in the cloud tops, and its depth increases with the seeding progress. The channel depth is about 700 m at cross section 9 and about 1500 m at cross section 2. The cloud thickness from the visible base to top is km, and there is still about 1 km thick cloud depth left below the channel. The earlier experiments showed that seeding supercooled stratiform clouds with depth smaller than 1 km could leave a clear track that could reach a width of 3 km in 35 min, and exist for more than 2 h. Seeding for thicker layer clouds caused glaciation, but often did not cause holes in the clouds (Langmuir, 1961; Mason, 1962). Fortunately, the satellite observed such a cloud seeding effect in thick supercooled stratiform clouds that it produced a channel lasting for 80 min, with width up to 14 km and depth up to 1.5 km. The cloud seeding enlarges the size of cloud particles. R e of ambient clouds around the track is about µm, and mostly less than 15 µm. However, R e inside the track exceeds 15 µm, and reaches a maximum of 26 µm, which is consistent with the threshold of effective radius causing precipitation (Rosenfeld and Gutman, 1994). The cloud seeding warms the track. With the progress of glaciation, the temperature difference increases within the track for the brightness temperatures of Channels 4 and 5, and their BTD also gradually increases. The channel in the visible image, the warming of the cloud tops in the seeded track, and the increase of BTD in the seeded track all demonstrate that the seeded cloud becomes thinner, apparently because the cloud top descends and it loses water to precipitation throughout its depth. The glaciation of clouds for this cloud seeding operation appears about 22 min after seeding (to the south of point G along line G H in Fig.2), which is estimated by comparison between the distance from the appearing point of the seeded track to point G with the distance and time the aircraft traveled from G to H. The first manifestation of the seeded track appearance is the reduced reflectance at 3.7 µm, which reflects the onset of glaciation to the point of being discernable by the satellite. Soon after that the visible cloud tops appear to start sinking, as seen

9 232 ACTA METEOROLOGICA SINICA VOL.21 just to the south of the location of point G in Fig.3c. This starts to appear as warming of the cloud top temperature at about 27 min after seeding, or 5 min after satellite detected onset of glaciation, as seen just to the north of the location of point G in Figs.3a, b, and c. The increase in BTD appears simultaneously with the appearance of glaciation. It is worth noting that in spite of the increased BTD, the visible (0.6 µm) reflectance in the seeded track did not decrease at all and even somewhat increased. This indicates that the clouds were still quite thick and contained much water in various forms. This combination of moderate BTD values with high visible reflectance is typical of mature glaciated precipitating clouds. The glaciation advances and releases latent heat that causes the air to rise in the middle of the seeded track and form a cloud line of small supercooled droplets just in the middle of the channel caused by the sinking of the glaciated cloud tops. This starts shortly after point F, and can be seen obviously in Fig.2. The age of the seeding track at this point is about 37 min after seeding. The growth of small water clouds inside the seeded track keeps occurring intermittently until point C, which is 62 min after seeding. The disappearance of these mid-track water clouds later suggests that the seeded track has matured and no additional latent heat of freezing is being released. However, this kind of water cloud inside the seeded track did not appear from points A to C, which suggests that the maturation of the seeding track was associated with its narrowing and eventual dissipation due to expansion of the tops of the ambient clouds from the sides inward. 7. Conclusions Cloud seeding in thick supercooled stratiform clouds did cause the change of microstructure and microphysical properties of seeded clouds, which can be clearly detected by the NOAA satellite. The retrieved properties of the seeded track suggest that cloud seeding glaciated the cloud through a deep layer and initiated the precipitation processes as intended. The satellite view allows observing the scale of the seeding effects on temporal and spatial scales. The spectral characteristics and cloud microphysical properties were analyzed, e.g., brightness temperatures of Channels 4 and 5, their brightness temperature difference (BTD), the particle effective radius inside and outside the cloud track, and the characteristic differences between them were compared, and the microphysical signatures of cloud seeding were revealed. The cloud seeding effects in thick supercooled stratiform clouds produced a channel lasting for 80 min, with width up to 14 km and depth up to 1.5 km. The cloud seeding enlarged the size of cloud particles. The effective radii of ambient clouds around the track were about µm, and most were greater than 20 µm inside the track. The ambient clouds were composed of supercooled droplets, while the cloud within the track was of ice particles. With respect to rather stable reflectance of two ambient sides around the track, the visible spectral reflectance in the channel of seeding cloud track varied at least 10%, and reached a maximum of 35%, the reflectance of 3.7 µm in the channel of seeding cloud track relatively decreased at least 10%, and the maximum variation exceeded 40%. As cloud seeding advanced, the cloud top temperature in the tracks became progressively warmer with respect to the ambient clouds, the maximum temperature differences reached 4.2 and 3.9 C at the first seeding position for Channels 4 and 5. In addition, the BTD in the tracks also increased steadily to a maximum of 1.4 C, contrast to C of the ambient clouds. The evidence that the seeded cloud became thinner came from the visible image showing a channel, the warming of the cloud tops in the seeded track and the increase of BTD in the seeded track. The seeded cloud became thinner because the cloud top descended and it lost water to precipitation throughout its depth. For this cloud seeding case, the glaciation became apparent at cloud tops about 22 min after seeding. The formation of a cloud valley in the supercooled stratiform clouds was mainly because that the seeded cloud volume glaciated into ice hydrometeors that

10 NO.2 DAI Jin, YU Xing, Daniel ROSENFELD and XU Xiaohong 233 precipitated and so lowered cloud top height. A thin line of new water clouds formed in the middle of the seeded track between 38 and 63 min after seeding, probably as a result of rising motions induced by the released latent heat of freezing. These clouds disappeared in the earlier segments of the seeded tracks, which continued to expand throughout the observation period of more than 80 min. Eventually the seeding tracks started to dissipate by expansion of the ambient cloud tops inward from the sides. Hopefully, this demonstration of satellite capabilities to detect seeding effects on supercooled clouds will bring advancement in the field. It opens new possibilities of using satellite for directing and monitoring weather modification experiments and operations. REFERENCES Albrecht, B. A., 1989: Aerosols, cloud microphysics and fractional cloudiness. Science, 245, Coakley, J. A., R. L. Bernstein, and P. R. Durkee, 1987: Effects of ship-stack effluents on cloud reflectivity. Science, 237, Inoue, T., 1989: Features of clouds over the Tropical Pacific during Northern Hemispheric winter derived from split window measurements. Journal of the Meteorological Society of Japan, 67, Langmuir, I., 1961: Collected Works of Langmuir. Vols. 10 and 11, Suits G., and H. E. Way, Eds., Pergamon Press, New York. Liu Jian, Xu Jianmin, and Fang Zongyi, 1998: Analysis of the cloud properties using NOAA/AVRHH data. Quarterly Journal of Applied Meteorology, 9, (in Chinese) Liu Jian, Xu Jianmin, and Fang Zongyi, 1999: Analysis of the particle sizes at top of cloud and fog with NOAA/AVRHH data. Quarterly Journal of Applied Meteorology, 10, (in Chinese) Mason, B. J., 1962: Clouds, Rain and Rainmaking. Cambridge University Press, 189 pp. Radke, L. F., J. A. Coakley, and M. D. King, 1989: Direct and remote sensing observations of the effects of ships on clouds. Science, 246, Rosenfeld, D., 1999: TRMM observed first direct evidence of smoke from forest fires inhibiting rainfall. Geophysical Research Letters, 26, Rosenfeld, D., 2000: Suppression of rain and snow by urban and industrial air pollution. Science, 287, Rosenfeld, D., and G. Gutman, 1994: Retrieving microphysical properties near the tops of potential rain clouds by multispectral analysis of AVHRR data. Atmos. Res., 34, Rosenfeld, D., and I. M. Lensky, 1998: Spaceborne sensed insights into precipitation formation processes in continental and maritime clouds. Bulletin of American Meteorological Society, 79, Rosenfeld, D., and W. L. Woodley, 2003: Closing the 50- year circle: From cloud seeding to space and back to climate change through precipitation physics. Cloud Systems, Hurricanes, and the Tropical Rainfall Measuring Mission (TRMM). Wei-Kuo Tao and Robert Adler, Eds., 59-80, Meteorological Monographs, 51, AMS. Rosenfeld, D., R. Lahav, A. Khain, and M. Pinsky, 2002: The role of sea-spray in cleansing air pollution over ocean via cloud processes. Science, 297, Rudich, Y., O. Khersonsky, and D. Rosenfeld, 2002: Treating clouds with a grain of salt. Geophysical Research Letters, 29, Woodley, W. L., D. Rosenfeld, and A. Strautins, 2000: Identification of a seeding signature in Texas using multi-spectral satellite imagery. J. Wea. Mod., 32, Yu Xing, Dai Jin, Lei Hengchi, Xu Xiaohong, Fan Peng, Chen Zhengqi, Duan Changhui, and Wang Yong, 2005: Physical effect of AgI cloud seeding revealed by NOAA satellite imagery. Chinese Science Bulletin, 50, (in Chinese) Zhang Jie, Li Wenli, Kang Fengqin, Qu Yongxing, and Sun Xuyong, 2004: Analysis and satellite monitoring of a developing process of hail cloud. Plateau Meteorology, 23, (in Chinese) Zhang Jie, Zhang Qiang, Kang Fengqin, and He Jinmei, 2004: Satellite spectrum character of hail cloud and pattern of remote sensing monitoring in east of Northwest China. Plateau Meteorology, 23, (in Chinese) Zhang Wenjian, Xu Jianmin, Fang Zongyi, et al., 2004: Theory and Methods of Satellite Remote Sensing of Rainstorm System. China Meteorological Press, Beijing, (in Chinese)