Spatial Distributions And Vertical Structures Of Multilevel Warm Cloud Systems Over Global Oceans

An accurate measurement of the vertical structure of clouds at the global scale has important implications for studying the macro and microscopic physical properties of clouds,cloud radiative forcing,and the development of climate models.The collocated data from quasi-synchronous Aqua/MODIS and CloudSat/CPR measurements during 2008 are used to investigate the spatial distributions and vertical structures of multilevel warm cloud systems over global oceans.By modifying the traditionally warm cloud determination scheme that is based singly on cloud top temperature criterion,all cloud layers containing warm cloud monomers were classified and counted.The proportions of the dominant 1-4 layer clouds were:68.43%,20.27%,7.8%,and 2.5%,respectively.In the global distribution,the difference between the single-layer clouds and multi-layer clouds is obvious,especially on the geolocation with frequent occurrences.However,the distribution of 2-4 layers of clouds is very close,and densely-distributed areas and sparse areas are highly coincident.In this paper,single layer warm cloud,double layer semi-warm cloud and double layer warm cloud are further studied,due to the absolute dominant position of the single cloud and double cloud in frequency and the similarity of the multilayer cloud distribution.The statistical results show that on the global scale,the proportions of the three configurations are 77.14%,19.15%,and 3.71%,respectively.In the global distribution,the difference between the three configurations of warm clouds is obvious.In terms of structural parameters such as cloud top height,cloud base height and cloud thickness,the statistical characteristics of the lower warm cloud in double layer semi-warm cloud is very close to that of single layer warm cloud,showing the similarity of the two kinds of warm clouds on the geometric structure.This indicates that the upper cold cloud in double layer semi-warm cloud does not cause changes in the lower warm cloud,and the upper and the lower one are likely originated from independent cloud-formation processes.The structure of the upper warm cloud in the double layer warm cloud configuration is obviously different from that in the single layer warm cloud,while the lower one is close to that of single layer warm cloud,but with smaller cloud top height and cloud thickness.In addition,the thinner the lower warm cloud,the stronger the upper warm cloud can develop upward.These results suggest that there are probably relevance between the upper and lower warm cloud in double layer warm cloud,and these two cloud layers are closely correlated during their evolution.According to the analysis of the vertical structure of the reflectance in the clouds above the three typical warm clouds,the vertical distribution of the reflectivity of the three types of warm clouds,such as the single layer warm cloud,the lower layer of the double layer semi-warm cloud and the double warm cloud layer,has a very high similarity.The reflectivity profile is consistent with the dominant mode,and the minimum value appears mostly in the cloud top,and has a high heterogeneity in the vertical direction.The upper layer of the double warm cloud has very different vertical reflectivity distribution,which is mainly reflected in the difference of the dominant reflectivity profile and the degree of vertical uniformity.The above indicates that the upper layer of the double layer warm cloud is a unique kind of warm cloud monomer,and its development mechanism and microphysical properties may be very different from that of the general warm cloud monomer.