一次梅雨锋暴雨过程的数值模拟及机理分析

SIMULATION AND MECHANISM ANALYSIS OF A MEIYU FRONT RAINSTORM

对2003年6月24、25日的江南北部暴雨过程进行了数值模拟及其结果分析。研究表明:这是一次在高空槽、低空切变线及高低空急流的共同影响下,冷暖空气交汇形成梅雨锋而引发的降雨;在暴雨过程中,高低空急流的共同作用对暴雨的发生发展起着重要作用,风场的特殊结构,使得中空出现三个无辐散层、两个垂直上升运动中心,从而维持了整层的垂直上升运动;去除潜热的“干”敏感性试验表明,潜热释放加热了深厚的大气层,使得高层加压辐散,暴雨区北侧的高空西北急流加强,低层减压辐合,暴雨区南侧的低空西南急流加强,同时使得低层的切变线得以维持加强。

Based on the correct numerical simulation for a Meiyu front heavy rainfall during 24-25 June 2003 in the area south of the Yangtze River valley, this paper analyzes the mechanism for the rainstorm. The results show that, with the collective influence from an upper-level trough, low-level shear line and upper and low-level jets, warm and cold drafts converge and a Meiyu front forms to cause the rainstorm. During the event, the collective effect of the upper and low level jets is important, and the special velocity field results in three non-divergence layers and two centers of vertical velocity, maintaining deep ascending flows. The‘dry＇ experiment shows that, the latent heat release heats the deep atmosphere, strengthening the upper pressure and divergence, enforcing the upper-level northwest jet north of the rainfall. Furthermore, the effect of latent heat release makes the lower level decompress and converge, strengthens the lower-level southwest jet south of the rainfall, and maintains the low-level shear line.