关键词: 暴雨, 环境场分析, 斜压发展特征, 集合预报检验

Abstract:  A continuous rainstorm event in the middle of Shanxi Province during 1-3 August 2015 was analyzed by using meteorological observations and NCEP/NCAR reanalysis data. Based on the test of ECMWF ensemble forecast products, the joint probability method was used to improve the ensemble forecast of rainstorm. The results are as follows: (1) The precipitation was characterized obviously by convection in this event, which could be divided into two stages. The first stage was the sudden rainstorm in the front of the cold front. In the second stage, the heavy rainfall was caused by the regional strong convective weather, which was affected by the high trough, the low shear line, and the surface cold front. (2) The strong upward motion caused by the convergence of the lower level made many mesoscale convective cloud clusters merge and develop continually, which resulted in rainstorm directly. In the first stage, the convergence layer at the middle and low level was deeper, the suction effect at high level was stronger, and the precipitation rate was greater. In the second stage, the dynamic and energy disturbances at the lower layer were more obvious, and the precipitation area was more concentrated. (3) Mesoscale baroclinic diagnosis showed that, in the first stage, the convergence and frontogenesis of the wet Q-vector at the lower layer increased many times and caused the convective motion stronger and the range larger, and formed many rain peaks of the precipitation. While in the second stage, the baroclinic development of mesoscale system was stronger, but the thickness of instability decreased, therefore the precipitation intensity decreased. (4) The improved ensemble forecast product of the joint probability showed that the range of high probability coincided with the center of rainstorm.

Key words: heavy rainfall, environmental field analysis, baroclinic development characteristics, ensemble forecast test