【摘要】 利用M icaps常规资料,对2000—2004年30~50°N之间的沙尘暴日与高空急流的关系进行了统计,把与沙尘暴相伴的高空急流分为2类:单急流型和双急流型;沙尘暴多发生在高空西南和西北急流的左侧及其右后方,与西北+西南型高空双急流相伴的沙尘暴多出现在西北急流中心的左前方和西南急流中心的左后方以及西北急流中心的右前方和西南急流中心的左后方。还对沙尘暴典型个例的风场结构的垂直分布、环流场的垂直结构等进行了动力学分析,结果表明:影响沙尘暴的高空急流有单急流、双急流、甚至三急流;一般北支高空急流高度较低,中心多在300 hPa,南支高空急流高度一般在200 hPa,中心风速多大于北支急流,北支急流多随高度升高向南倾斜,南支急流随高度的升高向北倾斜,单急流型沙尘暴多发生于北支急流下沉支的南侧,双急流型沙尘暴发生于双急流合并下沉支的下方;不论是上升气流还是下沉气流均有可能产生沙尘暴:低层辐合、高层辐散导致的抽吸作用,可在近地层形成大风和沙尘暴,强的下沉气流可导致高层动量有效下传有利于沙尘暴的产生;在南、北支高空急流之间往往会形成一支环流促进沙尘暴的形成,所以不仅是北支急流,南支急流也对沙尘暴的发生和发展产生作用。更多还原

【Abstract】 Using the Micaps regular date,correlation and statistical analyses between sandstorm days and the upper level jet stream between 30～50°N during 2000—2004 are carried out in this study.The results show that the sandstorms accompanied by the upper level jets can be divided into 2 kinds:single jet stream pattern and double jet stream pattern.For single upper level jet patterns,sandstorm is likely to occur beneath the left side and right rear side of the upper level SW or NW jet stream;and for double(a NW plus a SW) jet streams patterns,sandstorm is likely to takes place beneath the left front side of the NW jet and the left rear side of the SW jet,or beneath the right front side of the NW jet and the left rear side of the SW jet.Dynamic analyses on the vertical distributions of wind filed structure and the vertical structure of circulation field for selected typical sandstorm cases are also carried out.The analysis results suggest that the upper level jet associated with sandstorms includes single jet pattern,double jet pattern and even trijet pattern;generally the height of the north branch upper level jet is lower,at 300 hPa,and the south branch jet is higher,at 200 hPa;the maximum wind speed of the south branch is greater than that of the north branch;the north branch jet tilts to the south with height,while the south branch leans northwards with height.Sandstorms for single jet pattern mostly occur beneath the south side of the descending leg of the secondary circulation of the north branch jet,and sandstorms for double jet pattern are likely to occur beneath the merged descending leg of the two jets,sandstorms could occur either in the desceing area of upper level jet or in the ascending area:in the ascending area,the suction resulted from the low level convegence and the upper level divergence induces the low level strong winds and sandstorms,and in the descending area,the downward transfer of upper level momentum is in favor of the genesis of sandstorm.Between the north and south branch jet streams there always is a vertical circulation cell,which facilitates the genesis of sandstorm,therefore both the north branch jet and the south branch jet jointly impact the genesis and development of surface sandstorms.更多还原