Researches On Long-term Variation Trends Of Cloud Amount And Optical Thickness In China And The World

The annual and seasonal distribution and variation trends of total cloud amount, low cloud amount, middle cloud amount, high cloud amount and cloud optical thickness over China were analyzed by using the monthly mean data of ISCCP D2 from 1983 to 2009. Results show that the total cloud and middle cloud amounts are large in southern China and small in northern China. In Qinghai-Tibet Plateau there are large high cloud amount but smaller low cloud amount. The total and middle cloud amounts increased in eastern China and decreased in western China during the studied period, but the low and high cloud amounts decreased in most areas of China. Seasonally, the total cloud amount increased in the north and decreased in the west in spring and autumn, while increased in most areas in summer and decreased in winter. The low cloud, middle cloud and high cloud amounts show different distribution and variation trends. The cloud optical thickness, which is larger in southern China than in northern China, increased in most areas.The annual and seasonal distribution and variation trends of the global total cloud amount and optical thickness were analyzed by using MODIS data from 2001 to 2013. Results show that the total cloud amount is larger on the sea than on the land. There are three areas of high total cloud amount in the latitudes near the equator, 40 degrees south latitude and 40 degrees north latitude. The low areas of total cloud amount situate on the Sahara Desert, Middle East, western America, south of Latin America, southern Africa, Western Australia and Antarctica. The main increased areas situate at low latitudes, especially ITCZ. The cloud optical thickness, which is smallest on the sea of low latitudes and deserts in Sahara and Arabia, is higher on the land than on the sea in the middle and low latitudes. Moreover, the cloud optical thickness decreases in most areas of middle and low latitudes.Additionally, the impacts of aerosol optical depth on the total cloud amount and cloud optical thickness over China were discussed by using MODIS data. The analysis of four typical areas shows that the total cloud amount and cloud optical thickness are large in the areas with high aerosol optical depth. The variations of the total cloud amount are positively related to the changes of aerosol optical depth in the north of East China, the middle of Northeast China and the east of Qinghai-Tibet Plateau. In addition, the variations of the cloud optical thickness are positively related to the changes of aerosol optical depth in Sichuan Basin and the east of Qinghai-Tibet Plateau. However, they are in a negative correlation in the north of East China and the middle of Northeast China. It means that the variation of cloud is affected by other elements besides aerosol.The latest satellite data were used to provide the distribution and variation trends of cloud amount and optical thickness over China and world in this paper. The impacts of aerosol optical depth on the cloud were also be discussed. These results can promote the researches of cloud in climatic change.