一次局地特大暴雨湿位涡的中尺度分析

A MESOSCALE STUDY ON MOIST POTENTIAL VORTICITY(MPV) OF A LOCAL HEAVY RAINFALL EVENT

利用一个考虑陡峭地形的１６层η坐标模式对１９９０年８月１４－１５日发生在湖北省远安县的一次局地特大暴雨过程进行数值模拟。在较成功的控制试验基础上，利用该模式输出结果研究了本次暴雨过程湿相对位涡的演变特征。结果显示，在暴雨发生发展阶段，有强的湿相对位涡负值中心相伴随。对湿绝对位涡方程的诊断分析表明，在暴雨发展阶段，湿位涡变率为正，说明此时对流不稳定已有较强释放，这时起主要作用的是网格尺度铅直通量辐合和次网格尺度的扭转效应；在暴雨消亡阶段，湿位涡变率为负，这主要是由气旋性涡度加强较快所致，对其起主要作用的是网格尺度的水平通量辐散和次网格尺度的铅直通量辐散。

By using a regional sixteen level η coordinate model which considerated the steep topography,a numerical simulation on a local heavy rainfall which occured in Yuan′an,Hubei province on August 14-15,1990 with the maximum rainfall 366 8mm in 4 hours is performed in this paper.On the basis of the well simulation,the developing characteristics of MPV of this heavy rainfall event were studied.The main results show that,in the developing stage of the heavy rainfall,the precipitation center accompanied by a negative center of moist relativity potential vorticity (MRPV).Results from the diagnosis of MPV equation indicate that,before the peak value of the precipatation,the varying rate of MPV is positive.It means that the convective instability has been released at that time.The dominant physical effects are the vertical flux convergence of mesh scale MPV and the twisting effect on subgrid scale.After the peak value,the varying rate of MPV is negative.This is resulted from the rapid strenthening of the cyclonic vorticity.The dominant physical effects are the horizontal flux divergence on mesh scale and the vertical flux divergence on subgrid scale.