一次山地积云并合扩展层化过程的数值模拟

Numerical simulation of cumulus merging and stratification in mountainous areas

因复杂地形下热力和动力抬升对近地面空气的扰动作用,贵州地区容易形成内部嵌有许多小对流单体的积层混合云。选取2005年5月29日发生在贵州省的一次积层混合云降水个例进行分析,并利用WRF模式模拟该云系的生成、发展过程。结果表明:积层混合云由积云并合扩展层化形成,其发展过程经历三个典型的并合阶段。云系的降水特点是降水范围很大,分布不均匀,雨区中存在多个强降水中心,降水量累计最大值可达60mm,且强降水中心与云中小对流单体的位置对应;积层混合云形成过程中,地面产生强降水的最终原因是,云并合过程中释放的不稳定能量改变了云中的气流场和含水量场。

Because of response of the surface air flow to the distinct thermodynamic and dynamic disturbances by the complex topography in Guizhou Province, the convective-stratiform mixed clouds in which several convective cells imbed occur frequently. A typical convective-stratiform mixed clouds system in Guizhou Province on 29 May 2005 is studied in detail with observation data and simulation results. Results show that the convective-stratiform mixed clouds system is formed by cumulus merging and stratification, and the formation process goes through three typical merging stages. Precipitation is widespread with inhomogeneous distribution, and several strong centers embedded in rain field, which locate in small convective cells with the maximum precipitation of 60 mm. In the formation process of convective-stratiform mixed clouds, the ultimate cause why the intense precipitation occurs is that wind field and water content experience dramatic changes by release of instability energy during this process.