| The cloud vertical structure features are very important not only for weather and climate study but also for weather modification, however there are few direct and efficient observation methods in operations. By comparison, the paper firstly selects the relative humidity (RH) threshold method as the method to analyze cloud vertical structure, and secondly the paper prudes its feasibility and availability by using data of ground based radar, space based radar, surface observation, ceilometer and cloud top height retrieved from FY-2C/D, and lastly applied research shows how the application of the method. The main results are as follows:The cloud vertical structure features can be analyzed from sounding data. The time evolution of clouds in a region can get though the time sequence analysis of sounding data from a site in that region, and spatial profile analysis for multi-sites will show the spatial structure features of different weather cloud systems.The analysis of freezing rain's temperature and humidity structure by using sounding data shows that, the main mechanism for the occurrence of freezing rain in our country is the warm mechanism, which accounts for 73%, while the ice-phase mechanism occupies only 27%. The freezing rain caused by warm mechanism does not have a high cloud top (less than 3km), while cloud top of freezing rain by ice-phase mechanism is relatively high (up to 9km). When freezing rain occurs the surface temperature (the temperature in instrument shelter) is lower than 0℃. The warm layer thickness of ice mechanism freezing rain is basically above 1km, and the maximum temperature of the warm layer is averagely higher than 3℃. The mechanisms for freezing rain in the North (the area north of latitude 30) are simple which are mainly occupied by ice mechanism, while in the South (the area south of latitude 30) both the two mechanisms exist, and affected by the terrain, usually in areas of high altitude there is more warm mechanism freezing rain than ice mechanism one.Using the relative humidity threshold method and data of two years from 2009 to 2010, and selecting 10 sites according to different geographical and climatic zones to analyze cloud vertical structure features, the results show that:in our country, the average cloud base height, cloud top height and cloud thickness are respectively 2361m,6383m and 4022m, cloudy days account for 68.4%, and in these days the monolayer clouds and multilayer clouds are half and half. Cloud structure features has the seasonal variation law, cloud base height changes little with the seasons, while cloud top height reaches its highest in summer and lowest in winter, and cloud thickness is consistent with the change of cloud top heightThere are regional characteristics of the cloud structure, especially the differences between humid areas and arid areas:in humid areas the cloud thickness and interlayer thickness is relatively thicker, while in arid areas cloud base height is higher but cloud thickness and interlayer thickness is thinner. In those areas, days without clouds are in a higher proportion, at 40% or more, even if there are clouds, monolayer clouds are in majority. In humid areas, proportion of days without clouds is small, at weather with clouds there are mainly multilayer clouds. Raining clouds and non-precipitating clouds have some differences that raining clouds' cloud base height is low and cloud top height is high, cloud thickness is thick and interlayer thickness is thin, but precipitating clouds are just the opposite.Using weather forecast scoring ways BS and TS, and referring different relative humidity thresholds to analyze scores, the optimum different relative humidity thresholds for judging clouds of responding different heights are got. After optimizing the series of the thresholds fatherly, a final set of methods is summarized, which is fit for using our country's secondly L-band sounding data to analyze cloud vertical structures.
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