一次积层混合云降水不同尺度结构的数值模拟

利用中尺度数值模式WRF-ARW（V3.2）对2009年4月18-19日发生在张家口地区的一次积层混合云降水进行了模拟,并结合观测资料从不同尺度对这次降水过程进行了对比分析.结果表明：700 hPa西风槽、850 hPa低涡是影响这次降水的主要天气系统,来自南方的暖湿空气和西北内蒙古低涡带来的水汽是这次降水的主要水汽来源,两股水汽在张家口附近低层出现了大尺度辐合,有利于该地区云系的发展、降水的形成;降水云系呈东北-西南向带状分布,带长约1 000 km,带宽300km,在大片的云带中分布着很多个小的高值中心,中心区域一般在几十千米;结合雷达回波可以看到在均匀的回波层中镶嵌着柱状对流回波,具有典型的积层混合云降水回波特征;沿着雷达回波做剖面,发现云中云水含量分布无论是水平方向还是垂直方向都是不均匀的,雨水的大值中心与上层的霰、雪的大值中心相对应,中心水平范围在1020 km.

Numerical simulation on a convective-stratiform mixed cloud precipitation in different scales

The precipitation of a convective-stratiform mixed cloud in Zhangjiakou during 18--19 April2009 is simulated using the mesoscale numerical model WRF-ARW （V3.2） and comparativelyanalyzed with the observation data in different scales.Results show that the west wind trough at 700 hPaand the low vortex at 850 hPa are the main weather systems responsible for convective-stratiform mixedcloud.The warm wet air from the southern and the low vortex from northwest Inner Mongolia are mainwater vapor suppliers, which converge in Zhangjiakou region and thus are conducive to cloud systemdevelopment and precipitation formation.The cloud system shows a NE-SW banded distribution, whichis 1 000 km long and 300 km wide, and has lots of cloud water centers, which are about tens of kilome-ters.The cloud system has the echo characteristics of typical convective-stratiform mixed cloud precipi-tation, such as columnar echo of cumulus cloud embedded in uniform echo layer. The cross-section ofradar echo shows that the cloud water content is heterogeneous either horizontally or vertically.The cen-ters of rainwater are corresponding with the centers of graupel and snow in the upper layer, with hori-zontal range of 10--20 km.