关键词: 回流暴雪, 急流, 诊断分析

Abstract: Based on the conventional observational data and the NCEP reanalysis data, the dynamic and thermodynamic characteristics of a heavy snow of return-flow event in the southern part of North China were analyzed. The results indicate that synoptic situation of this process is two troughs and one ridge. The influencing system leading to the heavy snow of return-flow event includes high level jet, westerly trough, low vortex shear and low level jet, and cold air in Northeast China triggers this event. The maximum precipitation occurs just at the changing period of southerly wind and northerly wind. Precipitation ends when northeasterly wind controls entirely the low level. The stacking of high level divergence and low level convergence, subsidence of positive vorticity in the high level causes strong precipitation, while the ascending movement center is fairly low. Warming and humidifying before snowfall and insertion of cold air in the low level make the south of North China locating in energy front area of θse and water vapor convergence area, which is benefit to the generation of heavy snow. Water vapor of return-flow event is mainly from the south, and it is transported indirectly by cold air from Northeast China in low level.