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利用1979-2013年春季一日四次的ERA-Interim再分析资料,使用趋势分析和合成分析等方法,对35年来春季(3-5月)西南低涡进行了统计分析.结果表明,1979-2013年春季西南低涡共出现262次,平均每年7.5次,其出现次数具有明显的下降趋势,并且具有显著的年际和年代际变化特征.年际时间尺度上,在春季西南低涡偏多年,影响西南低涡出现次数多寡的大气环流易在青藏高原(下称高原)南北部形成“北低南高”以及在贝加尔湖和日本海附近形成“东高西低”型的位势高度,而这样型态的位势高度分布,非常有利于高原南部的异常西风气流和高原东部的异常南风气流在高原东部四川盆地附近形成气旋性环流;在年代际时间尺度上,贝加尔湖附近位势高度出现正的年代际差值和乌拉尔山附近位势高度出现负的年代际差值,非常不利于北边的冷空气侵入我国四川附近,加之高原附近正的位势高度差值中心的存在,也不利于西南低涡出现次数的偏多,这两者是导致春季西南低涡在1989年发生年代际减少的重要原因.“,”Based on the four times a day ERA-Interim reanalysis data provided by ECMWF in the spring (March to May) of 1979-2013,the long-term trends,interannual variability and interdecadal variability of the number of spring southwest vortex are analyzed by using the methods of synthetic analysis,trend analysis and others.The result shows that the spring southwest vortex appeared 262 times in total and the annual average is 7.5 in 1979-2013.The number of the spring southwest vortex decline significantly in the 35 years,and the correlation coefficient with time is-0.652,which past the significance level of 0.001.There are also obvious interannual and interdecadal variations characteristics of the spring southwest vortex.The years with more spring southwest vortex are 1979,1980,1982,1984,1987 and 1988.The years with less spring southwest vortex are 2000,2004,2008,2009 and 2011.The number of the spring southwest vortex appears as interdecadal significant mutation in 1989,shifts from more to less.The characteristics of atmospheric circulation which have effect on the number of spring southwest vortex are similar in both interannual scales and interdecadal scales.On the interannual scale,no matter the atmospheric circulation of the years of more (or less) spring southwest vortex or the most (or the least) year of it,in the lower troposphere,the geopotential height difference value distribution which is low in the northern Qinghai-Tibetan Plateau but high in the southern plateau and which is low in Lake Baikal but high in the sea of Japan are conducive to form the west wind difference value in the southern plateau and the south wind difference value in the eastern plateau.They are in favor of the formation of the cyclonic circulation near the Sichuan basin,and this cyclonic circulation can promote the generation and maintenance of the spring southwest vortex.On the decadal scale,because the positive geopotential height decadal difference value near Lake Baikal and negative geopotential height decadal difference value near the Ural Mountains can against the north cold air invading Sichuan province in China,combined with the positive geopotential height difference center near the Qinghai-Tibetan Plateau,which is unfavorable to the occurrences of spring southwest vortex,the two are the important reasons of the decadal reduction of the spring southwest vortex in 1989.