Characteristics of cloud cover over the Sichuan-Chongqing region revealed by geostationary satellite data

This study is based on observations of meteorological satellites Fengyun-4A and Himawari-8 and combined with the unique terrain over the Sichuan-Chongqing region, which is divided into the eastern low-altitude and the western high-altitude regions. A high-resolution gridded cloudless background field is established for comparison of radiation between cloudless and cloudy environments. The detection of clear sky, water cloud, ice cloud, low cloud/fog, haze, and snow using threshold method is realized to improve the confidence of cloud recognition. Temporal and spatial distributions of all the above types are analyzed from 2016 to 2021. Results show that clouds in the Sichuan-Chongqing region have significant regional characteristics and generally show a notable difference between the east and the west. The overall pattern of cloud cover frequency is larger in the east and smaller in the west. The cloud cover frequency has a high-value center throughout the year, and the cloud cover area has obvious monthly variations. The cloud cover frequency in the eastern low-altitude region is 70%—80% all the year round, while in the western high-altitude region it is 50%—65%. The high- and low-value transition area of cloud cover frequency corresponds to the steep terrain area between the Qingzang plateau and Sichuan basin, and is related to terrain, water vapor condition, and atmospheric circulation characteristics. The cloud cover area in the eastern low-altitude region is relatively stable in each month, accounting for 60%—80%, while the difference is significant in the western high-altitude region. The ice cloud area in the eastern region and the total cloud area in the western region both exhibit significant monthly variations (single peaks) with respective peaks of 37% and 76% appearing in July. In these six years, the interannual fluctuation of all the types is relatively small, and the cloud cover area in the eastern region exceeds 70% throughout the year with water clouds accounting for the largest proportion (35%—40%), ice cloud accounting for the second largest (about 20%), and low cloud/fog accounting for the smallest (about 13%). The cloud cover area in the westernregion accounts for about 60% throughout the year (water clouds 24%—26%, ice clouds 22%—25%, and low cloud/fog about 10%).