一次东北冷涡过程的数值模拟与降水分析

本文利用WRF模式对2007年7月8日至12日的东北冷涡过程进行模拟。通过分析天气尺度背景场可知, 在对流层中高层出现干侵入过程, 干空气主要来源于我国内蒙古西部和东北冷涡的西北部, 随着东北冷涡一起呈涡旋状运动, 在对流层中层的干侵入更加明显; 东北冷涡的东部为水汽通量辐合区, 说明此处水汽丰沛, 该处的暖湿空气与干冷空气相汇, 有利于降水的生成。通过分析中尺度对流系统的地面和对流层中下层的风场结构可知, 中尺度对流系统易发生在东北冷涡东南侧和东北侧的气旋性曲率最大处, 此处的对流层低层易形成强辐合区, 而风场的水平辐合运动激发出垂直上升运动, 在对流不稳定区配合着强上升运动, 有利于对流系统发展而产生降水, 因此在低压系统东南侧及东北侧的 “气旋曲度” 区易形成降水。从对流涡度矢量的垂直分量可知, 在东北冷涡中的东南侧和东北侧, 对流涡度矢量的垂直分量对于中尺度系统的发生位置和降水区域有很好的指示作用。

A Numerical Study and Rainfall Analysis of a Cold Vortex Process over Northeast China

Using the WRF/ARW model to simulate a proceeding of cold vortex over Northeast China during 8-12 July 2007.The analysis of synoptic weather indicates that the cold air mass above the north of Lake Baikal moves to the cold vortex over Northeast China and enforces it.What is more,a part of the cold air transfers to the middle and lower troposphere from the tropopause,which causes the process of dry intrusion.Besides,in the east of cold vortex,there is the convergence of water vapor transport,which indicates the water vapor is plentiful there,and the intersection of the cold dry air and the warm wet air benefits the formulation of rainfall.The results of wind structure of mesoscale convective system(MCS) prove that the southeast and northeast parts of cold vortex,where there exists the maximum of cyclonic curvature,are the areas prone to MCS,which leads to the heavy rainfall.Finally,the vertical component of convective vorticity(CVV) is used to diagnose the location of MCS rainfall,and the corresponding of CVV and rainfall shows that CVV could indicate the area of rainfall.