Properties Of Ice Clouds Under Different Optical Depth And The Effects From Aerosol Over China Based On Multi-source Polar Orbit Satellite Data

Ice clouds are crucial to the Earth's radiation balance.Two active sensors,the Cloud Sat radar and the CALIPSO lidar,provide the opportunity to detect ice clouds over the global region.Data DARDAR?li DAR/ra DAR?combines these two active sensors advantages to derive ice cloud products,which make obtain optical thin and thick ice cloud vertical properties possible.Based on the data product DARDAR from January 2013 to December2016,the ice cloud occurrence frequency,horizontal and vertical distribution,seasonal variation and microphysical properties of various optical depth ice clouds in China were analyzed.The results show that the occurrence frequency of ice clouds is 52%over the last four years,which is higher in spring and summer than in autumn and winter and the occurrence height is mainly between 5 and 10 km.The mean ice cloud optical depth,ice water path,and effective radius of China are approximately 4,157 g?m^-2and 51?m,respectively.The properties of ice cloud in China not only have obvious regional and seasonal variation characteristics,but also related to the type of ice cloud defined by different optical depth?values.Optically thin ice clouds?0.03<?<0.3?and opaque ice clouds?0.3<?<3?are the most frequently observed in China which account for approximately 65%of all ice cloud samples and the high concentration area is in the Qinghai-Tibet Plateau.Except for the subvisual ice clouds??<0.03?,the main occurrence height of other types of ice clouds decreases with the increase of optical depth.Seasonal changes of different types of ice clouds are not obvious except for thicker ice clouds??>20?.The more thick ice clouds with?>3are more occurred in summer while the thin ice cloud with?<3 are more occurred in winter.In terms of microphysical properties,the ice water content?IWC?are changing with the variation of optical depth.The Probability Distribution Function?PDF?of subvisual ice clouds accumulate with the IWC distribution.However,the range of PDF increases with optical depth increasing and both of the IWC distribution range and mode value increase.The relationship between the effective particle radius and height of the ice cloud is more closely related to the optical depth.According to the vertical frequency distribution analysis,all types of ice cloud effective radius increases with height decreasing significantly,optically thinner ones??<3?frequency distribution almost unanimously,while thicker ones??>3?effective radius is generally larger.The ice cloud data from DARDAR are collocated with aerosol product data from MODIS to derive the aerosol-ice cloud sample data sets in China from 2014 to 2016.The relationship between aerosol optical depth?AOD?and the macroscopic characteristics of ice clouds shows that the occurrence frequency of ice clouds over China increases with the value of AOD,which is pronounced around the value of 0.3.However,this effect would limit the formation of ice clouds that leads to the low occurrence frequency of ice clouds.Affected by aerosols,the occurrence of ice clouds in northwestern China,northern China,and the Qinghai-Tibet Plateau increased significantly,with the smallest changes in southern China.The distribution of the occurrence height of ice clouds indicates that comparing with clean conditions,the amount of high-level ice clouds has increased under pollution conditions throughout the country.The variation of the vertical cloud amount is not obvious in the Qinghai-Tibet Plateau.However,the amount of ice clouds above 8 km has increased in the Southern areas while ice cloud occurs decreasing under 8 km.The relationship between aerosol and ice cloud properties shows that the aerosol has a significant impact on the optical thickness and ice water content of ice clouds when aerosol values are lower,which shows a positive correlation over China region.The influence of aerosols on the effective particle radius of ice clouds is more complicated.When the water vapor vapor are sufficient,the increase of aerosols content has little effect on the ice cloud particle radius.However,when the water vapor content is low,high-value aerosols will lead to form more small-sized ice crystals,leading the average ice cloud particle radius to decrease.Compared with clean conditions,the variation of the average particle radius of ice clouds in Northwest China,the North China and the Qinghai-Tibet Plateau is not evident,while the effective particle radius of ice clouds decreases significantly with the increase of aerosol values in the South areas.