1. Departure of Atmospheric Science, Sun Yat-Sen University, Guangzhou 510275 China 2. Macau Meteorological and Geophysical Service, Macau, China 3. Shenzhen Meteorological Bureau, Shenzhen 518040 China
Abstract:
The onset of South China Sea summer monsoon in 1998 occurred on May 21st. Using the U.S. National Centers for Environmental Prediction reanalysis data, this paper examines the physical process of the weakening of a subtropical anticyclone in West Pacific during the onset period using the Zwack-Okossi vorticity equation. Results show that during the pre-onset period, the positive vorticity advection in front of an upper tropospheric trough was the most dominant physical mechanism for the increase of the cycl...