内蒙古春季久旱转雨大气环流系统特征

System Characteristic of Atmospheric Circulation from Drought to First Effective Rainfall during Springtime in Inner Mongolia

利用1960—2009年春季内蒙古104个测站逐日降水量资料,统计出春季第一次有效降水作为久旱转雨天气过程,分析了近50年春季久旱转雨降水特征和年代变化,利用NCEP/NCAR再分析资料分析了久旱转雨的大气环流型。结果表明,20世纪60-80年代内蒙古春季久旱转雨天气过程平均为1～2次,90年代有3次,表明1998年以后出现的频次明显增多。60-80年代500hPa高度场在高纬度欧亚大陆地区为一脊一槽的环流形势,乌拉尔山为高压脊,西伯利亚地区维持一稳定的低涡槽系统,西风急流位于50°—60°N之间,内蒙古受强西风控制;中低纬度地区的西风槽成为久旱转雨的主要影响系统。1990-2007年500hPa高度场上,在高纬度地区东亚大槽位置偏北,欧亚大陆50°—60°N西风急流北抬至70°—80°N,中高纬度地区贝加尔湖到东北地区和蒙古高原为低涡,中低纬度地区多短波槽、脊活动。2008年和2009年又出现了60-80年代的环流特征。对500hPa环流系统进行了分型,得到3种类型:A型(蒙古冷槽(涡))、B型(贝加尔湖低涡)和C型(东北低涡)。这3种类型是造成内蒙古春季久旱转雨的主要环流系统。

Using the daily precipitation data at 104 stations in Inner Mongolia,the first effective precipitation event in spring of the past 50 years（1960-2009） have been investigated,The features of the spring precipitation events which happened after a long-term drought and the decadal variations were summarized.The atmospheric circulation patterns for the effective precipitation events were analyzed based on the NCEP/NCAR reanalysis data.The results indicate that the effective precipitation occurs just once or twice from 1960s to 1980s,which happens three times on average from 1990s to 2000s,and significantly increased after the 1998.For the precipitation events in the period of 1960-1990,there is a pattern of one-ridge and one-trough in the high latitude region on 500 hPa geopotential height field over the Eurasian continent.In this pattern,the Ural Mountains is high-pressure ridge,while a stationary trough appears over Siberia,the westerly jet is between 50°-60°N.Under this condition,the most area of Inner Mongolia is controlled by a strong western wind.This westerly jet trough over the mid-low latitude range plays a crucial role in an effective precipitation in springtime.The location of 500 hPa eastern Asian trough during 1990-2007 is more northward than that of normal,while the westerly jet over the Eurasian continent from 50°-60°N approache northward to 70°-80°N.In addition,there is a vortex over the region of the Lake Baikal,the Mongolian Plateau and northeastern region of China.In the region of the mid-low latitude,the short wave trough and ridge act frequently to result in effective precipitation in Inner Mongolia.The circulation characteristic emergenced in 2008 and 2009 is same as in 1960s-1980s.500 hPa circulations are classified into three types： A type is Mongolian cold trough（vortex）,B type is Baikal vortex and C type is Northeastern China vortex,which are the main atmospheric circulation components of leading to effective precipitation in spring of Inner Mongolia.