2001年春季中国北方沙尘暴的环流动力结构分析

Circulation Dynamical Structure in Course of Dust Storm Occurrence in North China in Spring of 2001

通过对 2 0 0 1年春季中国北方 5次沙尘暴的高度场、涡度场、散度场和风场的分析 ,研究了沙尘暴强盛期的环流动力结构。结果表明 ,在 5次沙尘暴强盛期有相似的环流动力结构特征。在沙尘暴强盛期的高度场上 ,蒙古国有深厚的低值系统 ,乌拉尔高压发展 ,其间的强气压梯度是沙尘暴的动力源 ;低值系统有正涡度中心支持 ,外围是负涡度区 ,其间有强涡度梯度带 ;低值中心伴随有低层辐合高层辐散的垂直结构 ,易于发生近地面大风和上升气流 ,有利于地面起沙上扬 ,形成沙尘暴 ;大风区与强涡度梯度带一致 ,强风速切变形成的涡度输送有利于加强低值系统 。

The fields of geopotential height, vorticity, divergence and wind speed as the circulation dynamical structure in course of the dust storm occurrence in north China in spring of 2001 are analyzed based on the NCEP/NCAR data. The results show that there are some similar circulation dynamical structure features in strong stage of the dust storms. There is a deep low pressure system over Mongolia and a well developed high pressure ridge system over Ural, and a strong pressure gradient between the both. It is the dynamical source driving dust. The low pressure system is supported by positive center of vorticity, the minus vorticity area around it and strong gradient zone between both. There is a verticalstructure with convergence at lower level and divergence at upper level in the center of system, it is favorable for occurring strong wind near ground and rising air stream which raise dust into the dust storm. The strong wind region is cosistent with the strong vorticity gradient zone. The vorticity transfer made by the strong wind shear strengthens the low pressure system and then enhances the wind speed further.