ANALYSIS OF THE WESTWARD EXTENSION OFWESTERN PACIFIC SUBTROPICAL HIGH DURING A HEAVY RAIN PERIOD OVERSOUTHERN CHINA IN JUNE 2005

The NCEP/NCAR Ⅱ daily mean reanalysis data and observed precipitation data are employed to investigate the westward extension of the western Pacific subtropical high (WPSH) during the heavy rain period over the southern China in June 2005. Results show that there may exist a relationship between the east-west shift of the WPSH and the process of a southern China heavy rain. The analysis indicates that the vertical motion in the WPSH area is mainly caused by the latent heat release of monsoon rain belts on its northern and southern sides. The vertical motion could cause the accumulation of air mass in the center and west of the WPSH, which leads to its strengthening. The appearance of the northern and southern monsoon rain belts could not only enhance the WPSH by strengthening the descending draft, but also excite the development of positive vorticity and restrict the WPSH's movement in the north-south direction. Moreover, the Indian monsoon rainfall to the west of the WPSH may excite the development of anticyclonic vorticity on its eastern side, which leads to the westward extension of the WPSH.