Gaoyuan qixiang (Jun 2024)
Analysis of Cloud Characteristics in the Loess Plateau Based on CloudSat-CALIPSO Satellite Data
Abstract
Clouds play an important role in the Earth-atmosphere system.To deeply analyze the cloud characteristics in the Loess Plateau region （LP）， the macro and micro physical characteristics of clouds were analyzed by using the CloudSat-CALIPSO data from 2007 to 2016 in four regions of the Loess Plateau， namely， semi-humid， semi-arid， arid， and cold arid.The findings indicate that： （1） In the LP， the annual average frequency of clouds exceeds 55%， with the highest frequency in spring and summer， and relatively lower in autumn and winter.The frequency of clouds in semi-humid region is higher than that in other regions.However， the months with the highest frequency of cloud occurrence in the other three regions are earlier than those in the semi-humid region.（2） The frequency of single-layer clouds is the highest in all regions， accounting for over 60% of the total cloud amount， with double-layer clouds being the main type among multi-layer clouds， accounting for about 25% of the total cloud amount.The seasonal variation of cloud height in each region shows that it is greater in spring and summer than in autumn and winter， and that it is greater in semi-humid region than in other regions in all seasons.The seasonal variation of cloud geometric thickness is not significant in all regions， which is between 1 km and 4 km， with mainly thin clouds， and 78.13% of the cloud geometric thickness is less than 2 km.（3） The annual average value of cloud liquid water content in all regions reaches more than 220.5 mg·m-3， about 6.5 times of the annual average ice water content.It is mainly distributed in the altitude below 8.5 km， and the liquid water content gradually increases as the altitude decreases， in which the cloud liquid water content in the semi-humid region is larger than that in other regions.The ice water content in each region is small throughout the year， mainly distributed in the altitude layer below 16.5 km.（4） The values of the effective radius of liquid droplets in each region are mainly concentrated in the range of 12~16 μm， with a maximum of about 24 μm in the spring in the semi-arid region； the maximum value of the effective radius of ice particles occurs in the summer in the semi-humid region.The values of droplet number concentration in all regions were concentrated at 60~80 cm3， which were smaller than the mean value of ice particle number concentration， with peaks occurring in the summer in all regions， and the peak of ice particle number concentration occurring in the spring in the semi-humid and semi-arid regions.The results of this study can help to understand the cloud characteristics of the Loess Plateau and provide a reference basis for the simulation of cloud characteristics in the Loess Plateau by regional climate models.
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