39Hydro Evolutionary Mechanism of Cloud Clusters Moving Eastward from the Qinghai Tibet Plateau

Using FY-2E satellite data from June to August 2010, 192 cases of eastward migration processes of plateau cloud clusters accompanied by downstream precipitation were identified within the range of 25-35ºN and 75 -125ºE. These cases were divided into two categories: enhanced and no-enhanced processes in the second-order stepped terrain area, with 114 and 78 occurrences, respectively. The enhanced eastward moving cloud clusters travel from the southeastern part of the plateau along two paths south and north of the Yangtze River to reach the second level stepped terrain area, while the no-enhanced eastward moving cloud clusters move straight eastward from the frequent occurrence area in the eastern part of the plateau to the second level terrain area. The Daba Mountains and Wuling Mountains in the east of Sichuan Basin and the eastern the Yunnan-Guizhou Plateau in the south are the frequent areas of MCS in the eastward moving cloud clusters of the plateau. MCSs mainly occur in June and July, with a lifespan of 5 hours during the enhancement process and 4 hours during the no-enhancement process. The daily variation and nighttime occurrence of MCS frequency in eastward moving cloud clusters within the secondary terrain area are significant, with two peaks: near midnight (main peak) and around 4:00 PM BT in the afternoon (secondary peak). The eastward migration of high-altitude cloud clusters strengthens in the secondary terrain area, and their circulation patterns mainly include four types: multi-wave type (16.4%), northern ridge and southern trough type (33.7%), westerly deep trough type (25.9%), and southern branch trough type (24%). In the middle and lower layers, there is a clear cyclonic circulation of low vortex in the southeastern part of the Sichuan Basin. The southwest airflow or southerly airflow in the southern part of the secondary terrain area is strong, transporting abundant warm and humid water vapor to the secondary terrain area, which is conducive to the continued development and strengthening of convective cloud clusters in the area as the plateau moves eastward