近50年环贝加尔湖区变暖对中国华北夏季降水的影响机理

Impact of the Surface Air Temperature Warming around Lake Baikal on Trend of Summer Precipitation in North China in the Past 50 Years

利用1951-2007年中国722站逐月降水观测资料、NCEP/NCAR再分析资料及1958-2002年逐月欧洲中心的ERA-40再分析资料,分析了近57年中国华北夏季降水的年代际变化特征,重点讨论了全球变暖背景下环贝加尔湖地表气温升高对中国华北夏季降水长期变化的影响机理。结果表明,华北夏季降水长期减少趋势与全球变暖存在密切联系,环贝加尔湖地区的地表气温升高是影响中国华北夏季降水长期变化的关键因子之一。根据热成风原理,该地区地表气温的持续升高导致蒙古国和中国华北区对流层温度经向梯度和纬向风垂直切变的减小,从而对流层的大气斜压性减弱,易维持暖性异常反气旋环流,导致环贝加尔湖地区气旋活动的频率和华北地区夏季降水持续减少。

The trend of summer precipitation in North China during 1951-2007 and its possible linkage to the surface air temperature in Northern Hemisphere is discussed on the basis of the monthly mean precipitation dataset at 722 stations in China,NCEP/NCAR monthly mean reanalyzed data,as well as ERA-40 monthly mean reanalyzed data from 1958 to 2002.It is found that the change of the surface air temperature（SAT） around Lake Baikal is one of key factors to affect the North China summer rainfall anomaly on interdecadal time scale.Evidences suggest that the warming of SAT around Lake Baikal can decrease the meridional temperature gradient in the lower and middle tropospheres over Mongolia and North China,weaken the vertical zonal wind shear and the atmospheric baroclinicity in the troposphere,maintain an anomalous warmer anticyclone in the troposphere over Mongolian region,which weakens activities of Mongolian cyclone and results in the decrease of precipitation in North China.