海雾的准周期振荡特征

根据南海北部海雾外场观测获取的高分辨率液态含水量、长波辐射通量数据,采用小波分析方法分析了2008年3月16—17日和18—19日两次海雾中的液态水含量、净长波辐射通量的变化特征,讨论南海北部海雾发展和维持的冷却机制。结果显示:(1)无论在有云或无云条件下,海雾都可发展和维持;但前者的液态含水量明显小于后者,而风速大于后者;(2)在地面海雾的生成之前和生成初期,净辐射通量都存在准周期振荡现象,无论无云/有云,地面海雾液态水的大幅度发展的阶段都存在含水量的准周期振荡现象;(3)含水量的准周期振荡现象与振荡发生时段的长波辐射通量关系不大,而主要通过湍流对液态水的混合作用与高空海雾液态水大量生成阶段的雾顶长波辐射间接相关。(4)海雾的生成都与雾顶长波辐射冷却密切相关,但发展和维持可通过不同的冷却机制,既可通过海气间湍流热量输送和辐射传输,也可通过雾顶长波辐射冷却。     

Macro- and Micro-Structures of Heavy Fogs and Visibility in the Dayaoshan Expressway

Belonging to the southern subtropical moist type of monsoon climate, the Nanling mountainous area experiences heavy fogs whenever quasi-stationary fronts appear there from September to May. There can be as many as 15-18 days of heavy fogs per month. Fogs have more serious consequences in the Lechang-Ruyuan section of the Beijing-Zhuhai Expressway (the longest expressway in China) that passes through the main part of the Nanling Mts., where the road rises from 200 m to more than 800 m above sea level (ASL).For a major motorway in the mountainous areas of Nanling Mts., two multidisciplinary integrated field observations were carried out, which measured visibility by the naked eyes, visibility by instrument, spectrum of fogdrops, liquid water content (LWC) of fog, tethered sounding, dual-parameter low-level sounding, turbulence diffusion within fog layers, aerosol spectra of size and composition, sampled fog water compositions, and sampled rainwater compositions. Typical cases were probed for their analyses of synoptics, micro- and macro-structures and microphysics. It is understood that heavy fogs take place with high frequency in the area and bring about serious consequences. Being typical advection and upslope fogs, they are in essence low-lying clouds appearing at high altitudes,which are closely related with the activity of South China frontal processes, especially the South China quasi-stationary fronts, and reflect on the role of local terrain as well. The heavy fogs are characteristic of long duration, extremely low visibility, well-organized lump-shaped structure, large-size fog-drops, moderate concentration, high LWC, and stronger turbulent diffusion within the fog layers than in ne sky. They di er much from radiation fogs, which are better documented in previous study in China. It is found that fog LWC is in significant anti-correlation with visibility so that large LWC is associated with small visual range. It is also noted that one of the reasons for the fluctuation of characteristic quantities of micro-structure such as the LWC of fog in the area is, in addition to the inhomogeneous structure of the fog itself, the effect of advection and inhomogeneous underlying surface;during the translation of fog with the ambient wind, irregular upslope and cross-over movement is another reason for the inhomogeneous structure and fluctuation of fog. The spectrum of the aerosol size displays itself as the power function of monotonous descent. The concentration of submicrometer particles is even higher. The high-concentration sulfate particles found in the aerosols of Nanling Mts. are actually good nuclei for condensation, which are favorable for the formation of fog. The presence of fog can help cleanse the trace compositions in the atmosphere so that fog droplets contain high levels of polluting elements. In the meantime, compared to cloud droplets, fog droplets are easier to be captured by the vertical surfaces of objects on the land surface, such as vegetation and buildings to constitute another kind of cleansing process.In vast stretches of forest like the Nanling Mts., this kind of cleansing may be quite important. Studying the characteristic variation of fogs in the area realistically assists in setting up a forecast and warning system for local fogs and provides basic information for fog dispersal experiments.     

A New Tethered Balloon-Borne Payload for Fine-Scale Observations in the Cloudy Boundary Layer

A new scientific payload is introduced for fine-scale measurements of meteorological (wind vector, static air temperature, humidity, and air pressure) and microphysical (aerosol particles and cloud droplets) properties, suspended below a tethered balloon. The high resolution sensors and the tethered balloon are described. Measurements in a lifted fog layer from a first field campaign are presented.The detailed investigation of the fog/haze and the temperature inversion layer demonstrates the damping influence of the fog on temperature fluctuations, while thewind fluctuations are significantly decreased by theevolving temperature inversion, whichwas about 30 m above the fog layer.From spectral analysis the noise floors of the high-resolution sensors are determined to10^-6 kg m^-3 for the LWC (liquid water content) and 4 mK for the fast temperature sensor (UFT-B). The correlation betweentemperature and LWC structures in shallow haze layers is investigated. The release of latent heat and the corresponding warming in the haze of about 0.1 K could be quantified.     

Macro-and Micro-Structures of Heavy Fogs and Visibility in the Dayaoshan Expressway

Belonging to the southern subtropical moist type of monsoon climate,the Nanling mountainous area experiences heavy fogs whenever quasi-stationary fronts appear there from September to May.There can be as many as 15-18 days of heavy fogs per month.Fogs have more serious consequences in the Lechang-Ruyuan section of the Beijing-Zhuhai Expressway(the longest expressway in China)that passes through the main part of the Nanling Mts.,where the road rises from 200m to more than 800m above sea level(ASL).For a major motorway in the mountainous areas of Nanling Mts.,two multidisciplinary integrated field observations were carried out,which measured visibility by the naked eyes,visibility by instrument,spectrum of fog- drops,liquid water content(LWC)of fog,tethered sounding,dual-parameter low-level sounding,turbulence diffusion within fog layers,aerosol spectra of size and composition,sampled fog water compositions,and sampled rainwater compositions.Typical cases were probed for their analyses of synoptics,micro- and macro-structures and microphysics.It is understood that heavy fogs take place with high frequency in the area and bring about serious consequences.Being typical advection and upslope fogs,they are in essence low-lying clouds appearing at high altitudes,which are closely related with the activity of South China frontal processes,especially the South China quasi-stationary fronts,and reflect on the role of local terrain as well.The heavy fogs are characteristic of long duration,extremely low visibility,well-organized lump- shaped structure,large-size fog-drops,moderate concentration,high LWC,and stronger turbulent diffusion within the fog layers than in fine sky.They differ much from radiation fogs,which are better documented in previous study in China.It is found that fog LWC is in significant anti-correlation with visibility so that large LWC is associated with small visual range.It is also noted that one of the reasons for the fluctuation of characteristic quantities of micro-structure such as the LWC of fog in the area is,in addition to the inhomogeneous structure of the fog itself,the effect of advection and inhomogeneous underlying surface; during the translation of fog with the ambient wind,irregular upslope and cross-over movement is another reason for the inhomogeneous structure and fluctuation of fog.The spectrum of the aerosol size displays itself as the power function of monotonous descent.The concentration of submicrometer particles is even higher.The high-concentration sulfate particles found in the aerosols of Nanling Mts.are actually good nuclei for condensation,which are favorable for the formation of fog.The presence of fog can help cleanse the trace compositions in the atmosphere so that fog droplets contain high levels of polluting elements.In the meantime,compared to cloud droplets,fog droplets are easier to be captured by the vertical surfaces of objects on the land surface,such as vegetation and buildings to constitute another kird of cleansing process. In vast stretches of forest like the Nanling Mts.,this kind of cleansing may be quite important.Studying the characteristic variation of fogs in the area realistically assists in setting up a forecast and warning system for local fogs and provides basic information for fog dispersal experiments.     

Comparison of cloud properties between cloudsat retrievals and airplane measurements in mixed-phase cloud layers of weak convective and stratus clouds

Cloud microphysical properties including liquid and ice particle number concentration (NC), liquid water content (LWC), ice water content (IWC) and effective radius (RE) were retrieved from CloudSat data for a weakly convective and a widespread stratus cloud. Within the mixed-phase cloud layers, liquid-phase fractions needed to be assumed in the data retrieval process, and one existing linear (p1) and two exponential (p2 and p3) functions, which estimate the liquid-phase fraction as a function of subfreezing temperature (from -20°C to 0°C), were tested. The retrieved NC, LWC, IWC and RE using p1 were on average larger than airplane measurements in the same cloud layer. Function p2 performed better than p1 or p3 in retrieving the NCs of cloud droplets in the convective cloud, while function p1 performed better in the stratus cloud. Function p3 performed better in LWC estimation in both convective and stratus clouds. The REs of cloud droplets calculated using the retrieved cloud droplet NC and LWC were closer to the values of in situ observations than those retrieved directly using the p1 function. The retrieved NCs of ice particles in both convective and stratus clouds, on the assumption of liquid-phase fraction during the retrieval of liquid droplet NCs, were closer to those of airplane observations than on the assumption of function p1.     

Application of aircraft observations over Beijing in cloud microphysical property retrievals from CloudSat

Cloud microphysical property retrievals from the active microwave instrument on a satellite require the cloud droplet size distribution obtained from aircraft observations as a priori data in the iteration procedure.The cloud lognormal size distributions derived from 12 flights over Beijing,China,in 2008-09 were characterized to evaluate and improve regional CloudSat cloud water content retrievals.We present the distribution parameters of stratiform cloud droplet （diameter ＜500 tm and ＜1500 μm） and discuss the effect of large particles on distribution parameter fitting.Based on three retrieval schemes with different lognormal size distribution parameters,the vertical distribution of cloud liquid and ice water content were derived and then compared with the aircraft observations.The results showed that the liquid water content （LWC） retrievals from large particle size distributions were more consistent with the vertical distribution of cloud water content profiles derived from in situ data on 25 September 2006.We then applied two schemes with different a priori data derived from flight data to CloudSat overpasses in northern China during April-October in 2008 and 2009.The CloudSat cloud water path （CWP） retrievals were compared with Moderate Resolution Imaging Spectroradiometer （MODIS） liquid water path （LWP） data.The results indicated that considering a priori data including large particle size information can significantly improve the consistency between the CloudSat CWP and MODIS CWP.These results strongly suggest that it is necessary to consider particles with diameters greater than 50 tm in CloudSat LWC retrievals.     

Aircraft Measurements of Cloud–Aerosol Interaction over East Inner Mongolia

To investigate the potential effects of aerosols on the microphysical properties of warm clouds, airborne observational data collected from 2009 to 2011 in Tongliao, Inner Mongolia, China, were statistically analyzed in this study. The results demonstrated that the vertical distribution of the aerosol number concentration(N_a) was similar to that of the clean rural continent. The average aerosol effective diameter(D_e) was maintained at approximately 0.4 μm at all levels. The data obtained during cloud penetrations showed that there was a progressive increase in the cloud droplet concentration(N_c) and liquid water content(LWC) from outside to inside the clouds, while the Nawas negatively related to the Ncand LWC at the same height. The fluctuation of the N_a, Ncand LWC during cloud penetration was more obvious under polluted conditions(Type 1) than under clean conditions(Type 2). Moreover, the wet scavenging of cloud droplets had a significant impact on the accumulation mode of aerosols, especially on particles with diameters less than 0.4 μm. The minimum wet scavenging coefficient within the cloud was close to 0.02 under Type 1 conditions, while it increased to 0.1 under Type 2 conditions,which proved that the cloud wet scavenging effect under Type 1 conditions was stronger than that under Type 2 conditions.Additionally, cloud droplet spectra under Type 1 conditions were narrower, and their horizontal distributions were more homogeneous than those under Type 2 conditions.     

2006年12月南京连续4天浓雾的微物理结构及演变特征

2006年12月24-27日南京地区出现了连续4天的浓雾天气,其中能见度小于50 m的强浓雾持续了40多个小时.利用FM-100型雾滴谱仪,连续观测了雾滴谱、数密度和含水量等微物理参量.结合自动气象站及能见度仪观测资料,分析了这次浓雾过程的微物理特征,并与1996年观测结果进行对比:雾滴的平均含水量和平均直径与1996年观测结果相当,含水量最大值比1996年观测结果大4倍,数密度比10年前小.认为前2个子过程的雾滴数密度、含水量很高,造成了南京奉次大雾能见度长时间低于50 m的恶劣天气.结合边界层探空资料,认为形成这种强浓雾的主要原因足近地层持续存在强盛的水汽平流,具有平流雾的特征.根据雾微物理参量的起伏变化,将浓雾过程分成4个子过稃,分析并比较了4个子过程的雾滴谱分布,总过程的谱分布及4个子过程的谱分布都服从Dcirmendjian分布,谱型都基本呈指数下降,雾滴主要集中存小滴段.最后,对第一个子过程微物理参量的变化特征进行了细致分析.发现这次浓雾是在夜间晴空辐射降温后形成的,午夜最强,日出后随着气温的升高逐渐减弱,反映了辐射雾的口变化特征.另外,还发现雾形成以后,开始变化不大,但随着进一步辐射降温,地面雾团不断产牛,雾爆发性发展.     

一次高压型海雾中的液态含水量演变特征

2008年3月16—17日在粤西电白出现了一次在高压天气系统控制下的海雾过程。利用这次海雾的综合观测数据,分析了这一高压型海雾的液态含水量演变特征,讨论了液态含水量与雾滴平均直径和数密度以及气温、风速、湍流交换等的关系。结果显示:(1)海雾有发展-消散-再发展的准周期性变化特征;(2)海雾过程中的雾滴数有显著的变化,而雾滴平均直径的变化较小;雾滴数变化对海雾的发展、消散起主要作用;(3)在海雾生成和发展阶段,空气的冷却机制起主要作用;而在海雾的维持阶段冷却机制的作用并不明显;(4)在雾的生成阶段,弱湍流交换有利于雾的生成;而在雾的发展和维持阶段,湍流交换减弱,液态水增长,反之液态水减少。湍流交换的强、弱与海雾发展-消散-再发展的周期性变化有密切关系。     

Microphysical Structure and Evolution of a Four-Day Persistent Fog Event in Nanjing in December 2006

A persistent thick fog event occurred in Nanjing during 24-27 December 2006,and the bad visibility below 50 m lasted for more than 40 h.Microphysical characters and evolution of the fog event have been analyzed based on the continually observed data of drop-size distribution,number concentration,liquid water content(LWC),etc.,by an FM-100 fog particle spectrometer,as well as routine observations by an auto-weather station and a ZQZ-DN visibility meter during the fog episode.The results were compared with...     

用于研究冰雪晶生长的小型垂直过冷云风洞系统

研制了一个新的小型垂直过冷云风洞及其测试系统,实现了风、温数据自动采集,风洞内含水量测量方便易行.实验测量了温度-5—-18℃、含水量0.5—3.0g/m~3范围内冰雪晶生长的习性、下落速度、线性尺度增长率等诸参数.     

Vertical cloud structures of the boreal summer intraseasonal variability based on CloudSat observations and ERA-interim reanalysis

The boreal summer intraseasonal variability (BSISV), which is characterized by pronounced meridional propagation from the equatorial zone to the Indian Continent, exerts significant modulation of the active/break phases of the south Asian monsoon. This form of variability provides a primary source of subseasonal predictive skill of the Asian summer monsoon. Unfortunately, current general circulation models display large deficiencies in representing this variability. The new cloud observations made available by the CloudSat mission provide an unprecedented opportunity to advance our characterization of the BSISV. In this study, the vertical structures of cloud water content and cloud types associated with the BSISV over the Indian Ocean and subcontinent are analyzed based on CloudSat observations from 2006 to 2008. These cloud structures are also compared to their counterparts as derived from ERA-interim reanalysis. A marked vertical tilting structure in cloud water is illustrated during the northward propagation of the BSISV based on both datasets. Increased cloud liquid water content (LWC) tends to appear to the north of the rainfall maximum, while ice water content (IWC) in the upper troposphere slightly lags the convection. This northward shift of increased LWC, which is in accord with local enhanced moisture as previously documented, may play an important role in the northward propagation of the BSISV. The transition in cloud structures associated with BSISV convection is further demonstrated based on CloudSat, with shallow cumuli at the leading edge, followed by the deep convective clouds, and then upper anvil clouds. Some differences in cloud water structures between CloudSat and ERA-interim are also noted, particularly in the amplitudes of IWC and LWC fields.     

An algorithm for generating stochastic cloud fields from radar profile statistics

An algorithm is described for generating stochastic three-dimensional (3D) cloud fields from time–height fields derived from vertically pointing radar. This model is designed to generate cloud fields that match the statistics of the input fields as closely as possible. The major assumptions of the algorithm are that the statistics of the fields are translationally invariant in the horizontal and independent of horizontal direction; however, the statistics do depend on height. The algorithm outputs 2D or 3D stochastic fields of liquid water content (LWC) and (optionally) effective radius. The algorithm is a generalization of the Fourier filtering methods often used for stochastic cloud models. The Fourier filtering procedure generates Gaussian stochastic fields from a “Gaussian” cross-correlation matrix, which is a function of a pair of heights and the horizontal distance (or “lag”). The Gaussian fields are nonlinearly transformed to give the correct LWC histogram for each height. The “Gaussian” cross-correlation matrix is specially chosen so that, after the nonlinear transformation, the cross-correlation matrix of the cloud mask fields approximately matches that derived from the input LWC fields. The cloud mask correlation function is chosen because the clear/cloud boundaries are thought to be important for 3D radiative transfer effects in cumulus.The stochastic cloud generation algorithm is tested with 3 months of boundary layer cumulus cloud data from an 8.6-mm wavelength radar on the island of Nauru. Winds from a 915-MHz wind profiler are used to convert the radar fields from time to horizontal distance. Tests are performed comparing the statistics of 744 radar-derived input fields to the statistics of 100 2D and 3D stochastic output fields. The single-point statistics as a function of height agree nearly perfectly. The input and stochastic cloud mask cross-correlation matrices agree fairly well. The cloud fractions agree to within 0.005 (the total cloud fraction is 18%). The cumulative distributions of optical depth, cloud thickness, cloud width, and intercloud gap length agree reasonably well. In the future, this stochastic cloud field generation algorithm will be used to study domain-averaged 3D radiative transfer effects in cumulus clouds.     

Changes of cloud microphysical properties during the transition from supercooled to mixed-phase conditions during CIME

A ground-based seeding experiment using carbon dioxide and propane sprayed from pressurized bottles was carried out under supercooled cloud conditions on a small spatial and short time scale. Water vapor deposition on the artificially generated dry ice and propane ice germs as the main ice formation process (nucleation and growth) is consistent with the experimental results. After nucleation, diffusional growth of the ice particles, partly at the expense of evaporating small droplets, was identified during the mixing of the seeding line with the ambient supercooled cloud. Within the seeding plume, ice water contents up to 80% of the total condensed water are observed, although the size of the formed ice particles did not exceed 25 μm. From the changes of the ice and supercooled liquid phase with time under mixed-phase conditions, liquid water content (LWC) evaporation, ice water content (IWC) formation, and ice crystal growth rates are estimated, which are not affected by the artificial nucleation process. Thus, these rates are assessed to be applicable for a growing ice phase of small ice particles in a young mixed-phase cloud, where other growth mechanisms, like riming or aggregation, are negligible.     

降水条件下的云雷达与微波辐射计反演液态水含量对比分析

为了发展云雷达与微波辐射计联合反演液态水含量的方法, 利用2019年4—9月中国气象科学研究院在广东龙门开展的综合观测试验中的双波段云雷达和微波辐射计数据, 首先检验了在降水条件下微波辐射计天顶观测和斜路径观测两种探测模式反演温度(T)、相对湿度(RH)、液态水含量(LWC)和液态水路径(LWP)的合理性, 然后分析了两种探测设备反演LWC和LWP的差别。得到以下结论: (1)微波辐射计在斜路径观测模式下反演的产品受降水影响较小, 其反演结果明显优于天顶观测模式; (2)两种探测设备反演的LWP相关性较好且随时间变化较为一致, 但云雷达反演LWP与平均回波强度有明显相关, 随着雷达回波强度的增大, 云雷达与微波辐射计反演的LWP之比越大; (3)两种探测设备反演的LWC相关性较差且存在明显偏差, 在不考虑融化层的情况下单波段云雷达反演LWC与微波辐射计随高度变化趋势相近, 双波段云雷达反演LWC与微波辐射计反演结果在1 km及其以上区间存在明显差异。      

Ground-based remote sensing of LWC in cloud and rainfall by a combined dual-wavelength radar-radiometer system

This paper describes the retrieval procedure of liquid water content (LWC) in cloud or rainfall distri-bution by a combination of microwave radiometry and radar and its numerical simulation. The per-formance of a combined dual-wavelength (35.0& 9.375 GHz) radar-radiometer system for the remote sensing of cloud LWC and rainfall is given. During the two summers of 1980 and 1981, the preliminary obser-vations of different clouds and storms by the combined system and combined radar-radiometric cloud and rain parameter retrievals are carried out. Research results show that by the use of the combined radar-radiometric method, improvement are obtained in accuracy of rms LWC and rainfall over the pure radio-metric technique or the radar alone.     

Characteristics of Quasi-Periodic Oscillations During Sea Fog Events

Based on the high-resolution datasets collected in a sea fog field experiment at the northern coast of South China Sea, the variations of liquid water content (LWC) and net longwave radiation flux (NLRF) during two sea fog events on 16th-17th and 18th-19th March, 2008 are exaimeed by wavelet analysis, and the cooling mechanisms for fog formation and persistence are also investigated. The main results are shown as follows. (1) Sea fog may develop and persist whether it is cloudy or not aloft. However, when there is cloud aloft the LWC is less and wind speed in sea fog is higher than that in the clear sky. (2) The quasi-periodic oscillations (QPOs) of NLRF are observed in the formation stage of the two fogs. QPOs of LWC are only found in the developing stage no matter with cloudless or cloudy condition. (3) It is likely that sea fog forms by the cooling effects of longwave radiation and develops through the vertical mixing induced by the radiative cooling at the upper level. (4) During sea fog development and persistence, other mechanisms could also play important roles in fog-layer cooling, such as turbulent heat transport and radiation transport between air-sea interfaces.     

闽南沿海一次春季海雾过程微物理特征分析

利用地面自动站观测、风廓线雷达、ERA5再分析资料、葵花8号高分辨率卫星资料以及FM-120型雾滴谱资料,分析了2019年4月7日闽南沿海一次强浓雾过程的环流形势以及微物理特征。环流形势分析表明,此次海雾过程500 hPa为槽底偏西西北气流,700 hPa至地面为一致的偏南气流,探空形势稳定。海雾发生前,整层风速明显减小,弱风速层厚度迅速增大,为海雾的形成提供了稳定的环流背景。卫星监测分析表明,海雾首先快速形成于台湾海峡上,在偏南气流作用下,平流至沿海地区。水文条件分析表明,福建近海存在一条冷水带,从海峡中部至沿海海温梯度大,海温在18~24℃,近海气海温差介于0~2℃,有利于海峡内平流冷却雾的形成。雾滴谱分析表明,翔安站能见度显著下降伴随着粒子数浓度、液态水含量显著增加,雾滴谱爆发性拓宽。海雾过程中,5 min平均粒子数浓度最大超过200个·cm^-3,瞬时数浓度最大达到468个·cm^-3,雾过程平均数浓度为100个·cm^-3。5 min平均液态水含量最高达到0.41 g·m^-3,瞬时液态水含量最大达到1.35 g·m^-3,雾过程平均液态水含量为0.17 g·m^-3。粒子浓度呈现双峰结构特征,峰值分别位于4~6和22~26μm,表明小粒子和大粒子对海雾的形成均有明显的贡献。     

Some physical aspects of summer monsoon clouds—comparison of cloud model results with observations

The physical characteristics of the summer monsoon clouds were investigated. The results of a simple cloud mod-el were compared with the aircraft cloud physical observations collected during the summer monsoon seasons of 1973,1974,1976 and 1981 in the Deccan Plateau region.The model predicted profiles of cloud liquid water content (LWC) are in agreement with the observed profiles. There is reasonable agreement between the model predicted cloud vertical thickness and observed rainfall.The observed cloud-drop spectra were found to be narrow and the concentration of drops with diameter >20μm is either low or absent on many occasions. In such clouds the rain-formation cannot take place under natural atmos-pheric conditions due to the absence of collision-coalescence process. A comparison of the model predicted and ob-served rainfall suggested that the precipitation efficiency in cumulus clouds of small vertical thickness could be as low as 20 per cent.The clouds forming in the Deccan Plateau region during the summer monsoon are, by and large, cumulus and strato-cumulus type. The vertical thickness of the cumulus clouds is in the range of 1.0-2.0 km. The LWC is found to be more in the region between 1.6-1.9 km A. S. L., which corresponds to the level at almost 3 / 4 th of the total verti-cal thickness of the cloud and thereafter the LWC sharply decreased. Nearly 98 per cent of the tops of the low clouds in the region are below freezing level and the most frequent range of occurrence of these cloud-tops is in the range of 2.0-3.0 km A. S. L.. The dominant physical mechanism of rain-formation in these summer monsoon clouds it the col-lision-coalescence process.     

Instrument intercomparison study on cloud droplet size distribution measurements: Holography vs. laser optical particle counter

During the EUROTRAC Ground Based Cloud Experiment (GCE) 1990, a newly developed HODAR (Holographic Droplet and Acrosol Recording) was operated for the first time to measure cloud droplet size distributions by recording Fraunhofer in-line holograms of small cloud sample volumes in situ and analyzing the holographic images in the laboratory.This technical note compares the resulting size distributions with those obtained from two FSSP-100 laser optical particle counters. For all holograms analyzed during the GCE90 field experiment, the size distributions obtained from the two different methods agree well. Additionally, the liquid water contents (LWC) were measured directly by a Gerber particulate volume monitor PVM-100. The LWC calculated from the measured droplet size distributions deviate from the PVM-100 data.