Characteristics of the Subseasonal-Scale Zonal Movement of Subtropical High in Summer and Its Relationship with Precipitation in Southwest China

Western Pacific subtropical high (WPSH) is a large-scale circulation system that affects climate change in China. It is of great significance to study the influence of the subseasonal WPSH east–west movement on the precipitation anomalies in Southwest China. In this study, the WPSH east–west displacement index is first defined according to the main activity region of the WPSH in early and late summers. The index has a significant period of 10–30 d and can well indicate the WPSH zonal movement. A total of 195 east and west WPSH events (1374 d) are chosen based on the standardization index. The results show that the subseasonal WPSH zonal movement is closely related to the precipitation in Southwest China. During the west (east) events, the WPSH moves gradually as follows: east→west→east (west→east→west), and the rainfall in most of Southwest China changes as follows: less→more→less (more→less→more). The precipitation variation in Southwest China is closed related to the anomalous water vapor and atmospheric vertical movement in the northern side and main WPSH area. Furthermore, the results show that the precipitation anomalies in Guizhou and Chongqing are well coincident, which demonstrates the significant characteristics of the regional difference in Yunnan and Sichuan during the subseasonal WPSH movement, especially in Yunnan. In early summer, the precipitation anomalies in Yunnan are contrary to those in most of Southwest China, especially in Guizhou and Chongqing. For example, when the WPSH moves westward (eastward), the precipitation is less (more) in most of Yunnan; on the contrary, the precipitation in most regions of Southwest China is more (less). In the late summer, except the central and northern Yunnan, the precipitation anomalies in most of Southwest China are basically accordant.