Department of Resources,Environment and Geosciences,Yunnan University
The subtropical high of northwestern Pacific (abbreviated as WPSH) is a large-scale circulation system that affects on the climate in China. In this paper, the influence and the physical processes of the sub-seasonal east-west movement of subtropical high on the southwestern China are investigated. First, the east-west displacement index of the WPSH is defined according to the key position of WPSH movement in early summer and late summer. The index has a significant period of 10-30 days and represents well zonal shift of the WPSH. A total of 195 events (1374 days) are chosen based on standardization value of the index. The results show that the subseasonal scale zonal movement of the WPSH is a closed relation to the precipitation in the southwestern China. During the west (east) events, the WPSH move gradually from east→west→east(west→east→west), and the rainfall in most southwestern China changed from less→more →less(more→less→more). The response of southwest precipitation on the sub-seasonal scale to the WPSH change is closed related to the water vapor and vertical movement of the gas flow in the north side of the WPSH and the main area of the WPSH during the movement process of the WPSH. Otherwise, the analysis shows that, in the condition of the WPSH, the consistency of precipitation in Guizhou and Chongqing is good, but the regional difference of precipitation in Yunnan and Sichuan is very significant, especially in Yunnan. In early summer, in the process of the zonal movement of the WPSH, the precipitation in most parts of Yunnan is even contrary to that in most parts of southwest China, especially in Guizhou and Chongqing. Namely, when WPSH move westward, the precipitation is less in most regions of Yunnan, vise verse. In the late summer, the precipitation in north-central Yunnan is opposite to that in other regions.