黔西南一次中尺度暴雨的数值模拟诊断研究

使用WRF模式 (Weather Research and Forecasting model) 模拟了2006年6月12日贵州省西南部一次典型的突发性强对流暴雨过程, 模式较真实地模拟了这次局地发展的中尺度暴雨天气过程。对流层低层的中尺度辐合线造成了初始的上升运动, β中尺度对流系统首先在地面锋线前不稳定的暖区中生长, 辐合线南侧的偏南气流对水汽和热量的输送是对流能够持续生长的最重要因素。通过非地转ω方程的诊断证明, 在降水开始后, 凝结加热的释放对β中尺度对流系统的发展最为重要, 它强迫产生的上升运动分量超过了低层暖平流强迫造成的上升运动分量。在相应的热力、 动力结构的调整作用下, 对流层低层出现中尺度低空急流、 中尺度涡旋等动力结构。到降水过程后期, 由于偏北气流的侵入, 降水区上空对流层低层转为对流稳定的层结, β中尺度对流系统无法获得不稳定能量以维持其发展, 降水也逐渐减弱直至终止。

A Numerical Simulation Analysis of a Mesoscale Rainstorm System in Southwest of Guizhou Province

Using the Weather Research and Forecasting (WRF) model, numerical experiments are carried out to simulate a sudden severe rain in southwestern Guizhou Province on 12 Jun 2006. The results show that this severe rain is caused by locally rapid-developing meso-β-scale convective systems (M-βCSs) . At the beginning, the initial ascending movement was driven by the mesoscale shear line formed in the lower layer of atmosphere. M-βCSs were developing in the instable warm air in front of the surface cold front, the south wind transporting moist warm air on the south of the convergence zone was the most important factor for sustaining the development of these convective systems. Through diagnosis on the basis of ageostrophic omega-equation, it is showed that the release of condensation heating has an important effect on the development of M-βCSs, the ascending movement forced by it was greater than the contribution of the low-level warm advection. Through the thermodynamic and dynamic adjustment, some dynamic structures such as mesoscale Low Level Jet (mLLJ) and mesoscale vortex appear in the lower troposphere. Near the ending of the rain, the invading of the north flow made the lower layer of atmosphere convert into stable state from convective unstable state, so there was not enough instable energy for maintaining vertical motion, and the precipitation stopped in the end.