Characteristics Analysis of Cloud-Layer Thickness in East Asia Using Occultation Data

Based on the idea that getting cloud boundary height by using mutation of relative humidity profile when it comes into or out of clouds,we obtain the statistical characteristics of cloud-layer thickness in East Asia by using COSMIC occultation wet-air data from Jan.2007 to Jan.2009.The results show that minimum detecting altitude of COSMIC is lower than 3 km height,which mainly affects the retrieval of cloud-layer thickness of part middle-and low-level clouds.Occurrence frequencies of clouds along the direction of latitude and longitude show different distribution characteristics,and as altitude increases,frequencies of various types of clouds also have different variation regularity.Average thickness of all clouds in East Asia is 1.78 km,and single-layer cloud has the same distribution with highest-layer cloud,and two-layer and other-layer clouds have similar geographic distribution.Single layer cloud is relatively uniform in spring and autumn but the differences in summer and winter are relatively large.Two-dimensional frequency distributions of cloud-top height and layer thickness of highest-layer cloud in summer and winter are different,which mainly indicates that there are more thicker high clouds existing in upper troposphere in summer than in winter.