关键词: 急流, 暴雨, 环境条件, WRF模式

Abstract:  Using conventional surface and upper meteorological observations, wind profile radar data and WRF model data, this paper analyzed physical field and trigger conditions of a rainstorm process with low-altitude jet enhancing in Jiangxi. The results are as follows: (1) The rainstorm happened under the weather situation of subtropical high jumping northward and southwest jet strengthening, and it was caused by joint action of multi-systems such as subtropical high, short-wave troughs in the westerlies, monsoon, mesoscale convergence system and low-altitude shear. (2) Increase of both temperature and humidity in the low-level layer, invasion of cold convection in middle troposphere and abnormal value of all kinds of thermal instability indexes took high energy, high humidity and high instability over north of Jiangxi Province, and formed mesoscale θse energy front and dew point front over northeast Jiangxi. Frontogenesis was one of causes of this rainstorm. (3) Low-altitude jet strengthening brought enough water vapor and mesoscale convergence system developing along the jet produced mesoscale energy and temperature front. And condensation latent heating released by convective precipitation promoted meso-scale convective system. That helped strong rainfall. The jet pulsation with the speed more than 16 m·s-1 from 1.5 to 3 km  would forecast strong rainfall in downstream zone of southwest wind 1-3 hours in advance. (4) The 500 hPa positive vorticity advection developing increased the cyclone vorticity in middle troposphere, which caused positive vorticity column to grow, and made a secondary circulation with descending motion in the north of vorticity column. Meanwhile, high potential vorticity center developed downwards, which was favorable to cyclonic vorticity and frontogenesis development in low layer, promoting rising motion, and rainstorm keeping.

Key words: jet stream, rainstorm, trigger condition, WRF model