塔克拉玛干沙漠春季沙尘活动与西风急流位置变化的关系

Relationship between Spring Dust Activity and the Position Change of Westerly Jet in Taklimakan Desert

基于1980-2020年MERRA-2再分析资料和气象站点沙尘日数资料,利用定义的西风急流位置指数挑选了春季各月急流位置显著变化的年份,通过对比分析急流偏北和偏南年沙尘混合比、沙尘日数和大气环流场的差异,初步揭示了西风急流位置变化对塔克拉玛干沙漠沙尘活动的影响。研究发现:(1)春季各月西风急流的位置随年份呈现很强的波动性,且不同月份年际变化趋势不同,其经向移动主要是由沙漠上空南北温度梯度的变化引起的;(2)春季塔克拉玛干沙漠沙尘活动与西风急流位置变化有显著的相关性,当急流北移(南移)时,大气柱各层沙尘混合比均有显著的增加(减少);(3)春季塔克拉玛干沙漠沙尘日数与西风急流的南北移动紧密关联,急流北移将导致春季各月浮尘、扬沙、沙尘暴平均日数增加;(4)伴随春季西风急流北移,青藏高原及塔克拉玛干区域中高层大气被异常反气旋主导,沙漠上空西风急流增强,动量下传增加,同时低层大气出现异常东风,地表风速增强,显著影响了塔克拉玛干沙漠腹地沙尘的排放和输送。

Based on MERRA-2 reanalysis data and the dust records at meteorological stations from 1980 to 2020,we have defined the Westerly Jet stream Position Index(JPI)and provided preliminary insights into the impact of north-south movement of westerly jet stream on dust activity in the Taklamakan Desert(TD).By conducting a comparative analysis of the dust mixing ratio,frequency of dust events,and the atmospheric circulation fields during periods characterized by northward and southward shifts in the jet stream,we have derived the following conclusions:(1)The position of the westerly jet stream in spring exhibits obvious fluctuation between different years,and the interannual variation trend between different months is also different.The meridional movement is mainly caused by the changes of the north-south temperature gradient over the TD.When the temperature decreases in the southern regions and increases in the northern regions,the north-south temperature gradient decreases,causing the jet stream to shift northward.(2)The spring dust activity in the TD exhibits a significant correlation with the positional changes of the westerly jet stream.The dust mixing ratio within the atmospheric column experiences substantial increases(decreases)as the jet stream shifts towards the north(south).The difference in dust mixing ratio is greater in the lower layers than in the middle to upper layers.(3)The frequency of dust events in the TD during spring is closely correlated with the north-south movement of the jet stream.The northward shift of the jet stream leads to an elevation in the average occurrence of floating dust,blowing sand,and dust storms throughout each month in spring.The difference in the number of dust weather days caused by the positional shift of the jet stream is more significant in March and May compared to April.Especially episodes of floating dust,there is an average difference of up to 3 days between northward and southward shifts of the jet stream in May.(4)The northward migration of the westerly jet stream during spring alters the atmospheric circulation fields and exerts a profound influence on the emission and transportation of dust in the hinterland of TD.The abnormal anticyclone dominates the middle and upper atmosphere of the Tibetan Plateau and TD,intensifying the westerly jet stream over the desert and augmenting downward momentum transfer.Additionally,abnormal easterly winds manifest in the lower atmosphere,leading to an increase in the surface wind speed.These new findings will be helpful for understanding the formation mechanisms of spring dust activities in the TD and provide scientific basis and reference for climate change in the arid regions of Northwest China.