Characteristics Analysis on Heavy Rain over the Yangtze River Valley Induced by the Eastward-moving Cloud Clusters from the Tibetan Plateau

Based on the data from plateau observation test and reanalysis, the macro and micro parameters' characteristics of the eastward-moving cloud clusters over the Tibetan Plateau (TP) and the mechanism of heavy rains in the Yangtze River basin induced by the eastward-moving cloud clusters were studied. Initially finds are summarized as follows：Evolution of the cloud belt during eastward movement of the TP cloud clusters: when the cloud clusters move from the TP eastward to the middle reaches of the Yangtze River, the temperature of ice cloud top decreases, the height increases, and the effective radius decreases, indicating that the plateau convection system become enhanced with moving eastward. It should be noted that, the ice cloud shows weakening and dissipating state when it moves to northeast of Sichuan province, but it become strengthen again after merger with the convective cloud from the south, and move eastward to the middle reaches of the Yangtze River.

Energy conversion and wave-current interaction mechanism: the energy of middle and upper troposphere transmits from the TP to the east during the eastward movement of the plateau cloud cluster. The energy conversion occurs near the second-level topography in eastern Sichuan province, which is conducive to the strengthen of energy transmission. In the process of energy transmission, there are significant wave-current interactions. The average flow energy is transformed into disturbance flow energy, which indicates that the fluctuation of the plateau cloud clusters absorb energy from the base flow during eastward process. So that the convective disturbance become enhanced, prompting the cloud clusters to continue moving eastward and affecting the downstream region. At the same time, the interaction flow energy is also transformed into disturbance kinetic energy. Near the moment of heavy precipitation, the middle and lower troposphere in the Yangtze River Basin and its southern regions are characterized by a large concentration of water vapor