中文摘要：

基于1948-2013年NCEP/NCAR逐月逐日再分析资料、美国国家海洋大气局月平均海表温度资料,1958-2013年日本JRA-55再分析陆地雪深资料,采用850 hPa相对涡度场气旋追踪方法,统计了春季蒙古气旋的年际及年代际变化特征。根据蒙古气旋偏多年与偏少年的高度场环流背景,研究了影响蒙古气旋的主要环流系统。对北大西洋海温、欧亚大陆积雪深度分布对于蒙古气旋生成的影响进行了探讨。主要结论如下：（1）蒙古气旋活动具有明显的年代际变化特征。20世纪80年代初到90年代末期蒙古气旋数量处于下降趋势,2000年以后又处于增多趋势。（2）贝加尔湖西北侧的大气环流异常中心会对蒙古气旋的生成造成明显影响。冬季北大西洋格陵兰岛南部地区海温升高会在欧亚大陆激发遥相关波列,造成乌拉尔山以北地区的冬春季节雪盖深度的减小,雪盖深度减小产生的热力作用异常会造成贝加尔湖西北侧高度场的升高,导致蒙古气旋的减少。（3）乌拉尔山北部地区的冬季积雪深度可以作为预测春季蒙古气旋个数的前兆因子,其与春季蒙古气旋频次为正相关。

英文摘要：

Based on the four times daily NCEP/NCAR reanalysis dataset,NOAA sea surface temperature reconstruction dataset and JRA-55 reconstruction snow depth dataset,the 850 hPa relative vorticity cyclone tracking method was employed to identify the genesis regions in Mongolian cyclones for the years 1948 —2013 in spring.The inter-annual and inter-decadal variations of the frequencies of Mongolian cyclones were investigated.According to the geopotential height anomaly distribution of the years with high and low frequencies of Mongolian cyclones,the main circulation pattern which had significant impact on Mongolian cyclones was revealed.Meanwhile,the impact of snow depth and sea surface temperature on the Mongolian cyclones was analyzed.The main conclusions are as follows;（1） The frequency of the Mongolian cyclones has shown an decreasing trend in the beginning-1980 s and ending-1990 s,an increasing trend since the beginning of the 21 st century.（2） The circulation pattern to the northwest of Lake Baikal had a significant impact on the frequency of the Mongolian cyclones.The increased sea surface temperature in winter over the south of Greenland would induce a circulation pattern which could reduce the snow depth over the northern part of Ural Mountains.Then the decreased snow depth would lead to the positive height anomaly to the northwest of Lake Baikal.As a result,the frequency of the Mongolian cyclones would decrease.（3） The winter snow depth over the northern part of Ural Mountains in winter could be a predictor for the frequency of the Mongolian cyclones.There is a positive correlation between the frequency of Mongolian cyclones and the winter snow depth over the northern part of Ural Mountains.