2011年4月28—29日中国北方强沙尘暴发生机制位涡分析

A Potential Vorticity Analysis on the Occurrence Mechanism of a Strong Sandstorm in Northern China on April 28-29,2011

利用实况观测资料及NCEP1°×1°再分析资料和位涡理论,对2011年4月28—29日发生在中国北方的一次强沙尘暴发生机制进行研究。结果表明:500hPa强斜压槽为此次沙尘暴的主要影响系统,同时,高原到新疆低层暖高压为沙尘暴的发生提供了有利的不稳定条件;沙尘暴主要发生在地面冷锋后部,是一次锋面后部大风型沙尘暴过程,地面3h变压(▽P3)对沙尘天气的移动路径有明显的指示作用;强沙尘暴发生前CAPE增大,形成了有利的不稳定条件;500hPa位涡对沙尘暴影响系统有明显的指示意义,0.5PVU等值线可作为沙尘天气区的分界线;此次沙尘暴发生过程在位温剖面上表现为高纬的冷空气向低纬度扩展的过程;等熵面高值位涡系统由高层向低层下滑中,由于等熵面坡度增加和位涡守恒,使低层垂直涡度增大,导致地面气旋环流的发展和风速的增强,从而导致了此次沙尘暴天气的发生。

The occurrence mechanism of a strong sandstorm happened in northern China during April 28-29,2011 was analyzed with PV theory using the observed data and the NCEP recalculated data.The results showed that,the strong 500 hPa tilted trough was the main weather system that caused the sandstorm,while the low level warm high over Qinghai Plateau and Xinjiang province provided an instable condition beneficial to the sandstorm occurrence.This storm mainly occurred behind of the cold frontal surface.The surface three-hour air pressure variation had an obvious indication to the moving route of the sandstorm.The values of the CAPE increased before the occurrence of the sandstorm.This was beneficial to formaninstable condition.The 500 hPa PV had an obvious indication to the weather system and the 0.5 PVU contour could be regarded as a threshold of the sandstorm occurrence.The sandstorm occurred with the expansion of the cold air in high latitude to low latitude.The slowing-down of the high-value PV system to the low level enlarged the slope of the isentropic surface but did not change the PV conservation.This may result in the developing of the cyclonic circulation on the ground surface and the growing of wind,and finally induced the outbreak of the strong sandstorm.