一次强梅雨暴雨过程的数值模拟和伴随的中尺度系统分析

Numerical Simulation of a Mei-yu Front Heavy RainProcess and Analysis of the Concomitant Mesoscale System

利用PSU/NCAR的中尺度非静力数值预报模式MM5,采用高分辨率套网格方案和适当的物理过程,对2002年7月22日08时到23日08时的一次强梅雨暴雨过程和伴随的中-β尺度系统进行了数值模拟,模拟结果很好地描述了本次暴雨降水的时空分布及相伴随的中-β尺度系统的发生发展过程。试验结果表明,梅雨切变线上出现的一串中-β尺度系统是此次暴雨的直接影响系统;高空中尺度辐散系统的存在和变化方式对中-β系统的发展有重要的影响;中低层中尺度涡旋的形成会导致尺度更小的强冷暖平流的出现,从而进一步激励中尺度系统自身的斜压发展;降水潜热对暴雨的发展和维持也有重要的反馈作用。

Adopting a high resolution nested grid scheme and proper physical parameters,a Mei-yu heavy rain process in the middle reach of the Yangtze River from 0800 BST July 22 to 0800 BST July 23,2002 is simulated by use of PSU/NCAR mesoscale nonstatic numerical forecast model MM5 in this paper.The simulation results successfully describe the spatial and temporal distributions of the rain process and the developing course of the concomitant meso-β-scale system.The result shows that a series of meso-β-scale systems developing along the Mei-yu shear line are the direct influencing systems of this heavy rain process.The existence and changing fashion of the mesoscale divergence systems at high levels affect greatly the development of the meso-β-scale systems.The outgrowth of the mesoscale vortexes at low and middle levels could lead to the appearance of smaller scale strong cold and warm advection,which excites the baroclinic development of the mesoscale systems themselves.What's more,the latent heat of precipitation in turn have an important feedback effect to the development and maintenance of the heavy rain process,too.