Study On The Formation Mechanism Of Cirrus Clouds Over The Qinghai-Tibet Plateau In Summer Based On The Joint Satellite Data Of CloudSat And CALIPS

Cirrus clouds are a common type of cloud in the atmosphere,with an average coverage of about 40%of the Earth’s surface.Cirrus clouds are generally composed of non-spherical ice crystal particles and are located in the upper layer of the convective layer or the lower layer of the stratosphere,playing an important role in the Earth’s energy balance,radiation budget,and atmospheric water cycle.Due to the high altitude and unique physical characteristics of cirrus clouds,there is still a lack of systematic research on their spatial and temporal distribution,formation mechanisms,and climate effects.The selected study area in this paper is the Qinghai-Tibet Plateau.By integrating data from the"Cloud Sat"satellite and the"Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations"（CALIPSO）,a gridding processing approach was employed to investigate the spatiotemporal distribution characteristics of summer convective clouds over the Qinghai-Tibet Plateau from 2007 to2010.Additionally,in conjunction with other multi-source remote sensing data and reanalysis data,the study examined the generation mechanisms of convective clouds at a macro scale.Furthermore,by simulating and contrasting the microscale properties of convective clouds,the research investigated the generation mechanisms of microscale ice crystals within convective clouds.The main findings of the study are as follows::（1）The number of high-level cirrus clouds in the summer on the Qinghai-Tibet Plateau is much higher than that of low-level cirrus clouds,with high-level cirrus clouds mainly distributed in the southern region of the plateau,while low-level cirrus clouds have a higher frequency of occurrence in the western part of the plateau and on the edge of the plateau.The number concentration of ice crystal particles in cirrus clouds is much higher in the southern part than in the northern part,which is closely related to the frequent deep convective activity in the summer.Under the influence of aerosol ice nuclei,the size of ice particles in the north is much larger than that in the southern part of the plateau.（2）In the summer,the maximum frequency distribution of the altitude of cirrus cloud tops in the Qinghai-Tibet Plateau region is between 16 to 17 km,and the cloud base height is mainly distributed between 12 to 16 km.The size of ice particles is mainly concentrated between 10 to 20μm,and the ice water content is mainly distributed between 0 to 0.005 mg m^-3.（3）Deep convective activity significantly affects the generation of high-level cirrus clouds,especially strong deep convective activity which is conducive to explosive growth in the number of high-level cirrus clouds.The gravity wave dissipation contributes to the generation of cirrus clouds at different heights.Meanwhile,the obstruction and lifting effect of the plateau topography lead to the advection of water vapor and vertical upward air flow,providing sufficient water vapor and dynamic conditions for the generation of cirrus clouds at the southern border of the plateau.（4）The ice crystal number concentration of cirrus clouds shows a"V"-shaped distribution with vertical variation under homogeneous nucleation,and heterogeneous nucleation determines the peak value of the ice crystal number concentration.Different ice nuclei have different effects on the number concentration.