中国北方春季沙尘暴活动与高空西风急流变化的联系

Relation of Spring Dust-Storm Activities in Northern China and Changes of Upper Westerlies

利用1954-2007年中国国家气象信息中心提供的强沙尘暴序列数据集和美国国家环境预报中心与国家大气研究中心(NCEP/NCAR)提供的再分析资料,分析了30°N以北的中国北方沙尘暴活动与东亚高空西风急流变化的联系。结果表明,中国北方春季沙尘暴出现频数与亚洲大陆对流层高层200 hPa中纬度西风急流的位置和强度变化存在着密切的联系。这种关系在年际和年代际时间尺度上均得到体现,在多(少)沙尘暴活动年,急流轴位置比正常年偏北(南)。在研究时段内,沙尘暴活动呈现减少的趋势,同时高空西风急流表现出系统性南移趋势。这种相关性存在内在的联系,反映了高空西风急流轴位置变化对地面沙尘暴活动的影响:当春季200 hPa高空西风急流轴位置比正常偏南时,中国北边界至蒙古国一带的一个关键区(70°E-120°E,42.5°N-52.5°N)对流层高层西风显著减弱,该区高空急流减弱一方面通过动量下传造成沙尘源区低层西风减小,削弱沙尘暴产生所需的动力条件,另一方面使风切变和斜压性减小,不利于地面气旋的生成,从而使沙尘暴活动减少。

Based on the strong sandstorm sequence datasets produced by the National Meteorological Information Center and the NCEP/NCAR reanalysis data from 1954 to 2007,the connection between sandstorm activities in northern China(northward to 30°N) and changes of high-altitude westerly jet in East Asia was investigated.The results of correlation analysis show that the positively correlation is exist between the frequency of spring sandstorm in the northern China and the changes in the high-altitude westerly jet axis position which is significant at α= 0.01,with the correlation coefficient of 0.36,and the relationship exists both at the interannual and interdecadal time scales.The location of jet axis has northern(southern) movement during the years of more(less)sandstorm activities,compared with the normal year.The sandstorm activities exhibit a decreasing trend from1954 to 2007,and the high-altitude westerly jet axis moves southward systematically at the same time.Further analyses shows that the sandstorm activities is impacted by the position changes of high-altitude westerly jet axis.When position of upper westerly jet axis on 200 hPa moves southward in spring,the westerly in the northern boundary between China and Mongolia(70°E-120°E,42.5°N-52.5°N) becomes weaker,on the one hand,which lead to the surface wind in the dust source region decrease through the momentum downward transport,and constrain the power of sandstorm to break out;on the other hand,it reduces the wind shear and baroclinicity,limiting the generation of ground cyclones,finally leading to less sandstorm activities.