The Impacts of Atmospheric Moisture Transportation on Warm Sector Torrential Rains over South China

Abstract

Warm Sector Torrential Rains (WSTRs) occurring during the outbreak of the monsoon in May of 2015 in South China were studied using surface automatic weather observational data, sounding, European Centre for Medium-Range Weather Forecasts Reanalysis interim Data (ERA-interim), satellite and radar data, and a four-level nested grid simulation with the finest grid spacing of 1 km using the Weather Research and Forecasting model (WRF). The results show that the extreme precipitation event, which had maximum rainfall amounts of 406.3 mm in 10 h and 542.2 mm in 24 h on 20 May 2015, and was characterized by its rapid development and its highly concentrated and long duration of heavy rainfall, occurred over the trumpet-shaped topography of Haifeng. The simulation results indicated that the South China Sea (SCS) atmospheric moisture transportation (AMT) was crucial in triggering the precipitation of the WSTR over South China. The simulation of the WSTR was conducted by using the total energy-mass flux scheme (TEMF), which provided a reasonable simulation of the circulation and the vertical profile in the Planetary Boundary Layer (PBL) as well as the estimation of the precipitation. The AMT, which extends from the Beibu Gulf and the South China Sea to the coastal areas and provides Shanwei with a considerable amount of moisture in the boundary layer, and the effects within the PBL, which include orographic effects, an extra low-level jet, and a high-energy tongue characterized by a high-potential pseudo-equivalent temperature tongue with a warm and moist southwesterly wind, were the important large-scale factors causing the WSTR.