河西走廊“2010.04.24”特强沙尘暴特征分析

利用全天空成像仪、地面、高空气象观测资料、数值模式资料和NCEP/NCAR再分析资料,对2010年4月24日甘肃河西走廊的特强沙尘暴过程进行了分析。结果表明,从观测到沙尘至天空完全被沙尘遮蔽,仅仅只有2.5min;中西伯利亚—新疆北部的偏北大风携带着极地强冷空气入侵,造成了甘肃河西走廊的特强沙尘暴。进一步的分析还表明,沙尘区域上空存在一个西风急流中心,其高度在200-250hPa之间,沙尘暴爆发时,风速增大到40m.s-1,高度降低,范围扩大。由急流中心向地面伸展的最大风速带将高空动量向下传播,引发了河西走廊的沙尘暴;南北风的变化主要发生在250hPa以下,最大中心高度均位于400hPa附近,北风前锋到达之处,沙尘暴爆发;冷空气爆发时,首先造成地面气温的急剧下降,其次是700hPa和500hPa气温下降;地面热低压的强烈发展,一方面使气压梯度加大,另一方面导致边界层对流不稳定,二者的作用都增强了沙尘暴的强度。

Characteristic Analysis of the Severe Dust Event Occurred in Hexi Corridor on April 24, 2010

The features of dust event occurred in the Hexi corridor of Gansu province on April 24,2010 were analyzed,using the data measured by Total Sky Imager(TSI),routine surface and upper air measurements,numerical weather forecastproducts and NCEP/NCAR reanalysis data.The results show that it only took 2.5 minutes from the bright sky to totally be covered by dust.The northern wind from middle Siberia to north Xinjing with strong polar cool air caused the severe dust storm.Further analyses show that there was a center of westerly between 200 and 250 hPa over this region.The wind speed of the westerly center reached to 40 m·s~-1when the duststorm burst up,then the height of the center dropped down and extended.When the gale area extended from the upper level to near surface,the momentum of west wind would be transmitted downward.There were major changes of north and south wind below 250 hPa,the center of maximum wind speed was on 400 hPa.The duststorm broke when the frontier of north wind reached to the low level of south wind area.The outbreak of cold air led to the extreme air temperature decrease successivelyfrom near surface to 700 hPa and 500 hPa.The intense development of surface hot low-pressure system resulted in not only the increase of barometricgradient,but also the convective instability in boundary layer.The intensity of duststorm was enhanced by both of these consequences.