华南前汛期一次特大暴雨过程的数值模拟及其诊断分析

利用WRF3 DVAR同化常规观测和全国自动站资料的WRF模拟结果,对2010年6月18—20日华南前汛期一次特大暴雨过程发生发展的动力条件和热力条件进行详细的诊断分析和研究。结果表明,同化观测资料的WRF模式能较好地模拟出特大暴雨过程的强降水中心、雨带分布及降水强度的变化趋势。稳定的大尺度环流是特大暴雨发生的背景条件。高低空急流及其耦合产生的次级环流的建立是特大暴雨过程的主要动力机制。地面不稳定能量的累积和西南急流输送的充沛水汽和不稳定能量在强垂直运动作用下形成的湿上升,以及中高层冷空气在次级环流的下沉支作用下向低层侵入是特大暴雨过程的热力条件。湿位涡和锋生函数的诊断表明,对流层中高层的干冷空气在次级环流作用下向低层侵入与上升的暖湿空气相互作用,促使斜压不稳定和对流不稳定的释放和发展,是特大暴雨发生发展的触发机制。

NUMERICAL SIMULATION AND DIAGNOSTIC ANALYSIS OF A RAINSTORM DURING THE ANNUALLY FIRST RAINY SEASON OF SOUTH CHINA

With the outputs from the WRF model and the WRF 3DVAR model(version 3.2),this study gives detailed diagnosis and study of the thermal and dynamical conditions of a heavy rain that happened from June 18 to 20 during the annually first rainy season of South China.First,the simulation assimilated the data from regular observation stations and the automatic weather stations.The results showed that the distribution and intensity variations of the torrential rainstorm from the WRF model outputs were consistent with the observation.Second,a stable large-scale circulation was the background condition of this rainstorm.Third,an upper-level jet stream(ULJ),a lower-level jet stream(LLJ) and a vertical secondary circulation driven by them were the main dynamical mechanism of this process.Fourth,an ascending wet jet was induced by the continuous accumulation of convective available potential energy(CAPE) on the surface,and warm water vapor and unstable energy were transported by a southwest jet stream.This process was driven by strong vertical motion.Accompanied by dry intrusion driven by a dry cold from the mid-and upper-level invading the low level,the process served as the thermodynamic condition of this rainstorm.Finally,diagnose of the moist potential vorticity(MPV) and frontogenetical function indicated that the dry cold air from the mid-and upper-levels of the troposphere that invaded the lower level due to the secondary circulation interacted with the ascending warm,wet air flow from low levels,being conducive to the release and development of baraclinic instability and convective instability energy,which may have triggered the rainstorm.