Change of Large Scale Circulation and Its Impact on the Water Vapor over North China

Using the data of monthly precipitation at 25 stations form 1951to 2006 in North China and NCAR/NCEP monthly reanalysis datafrom 1948 to 2006,and the HYSPLIT_4 Model,the variation features of precipitationand the water vapor transportationin North China in summer(JJA)oninterdecadal and interannual time scales are investigated.The results show thatthe characteristic of water vapor transportation and it′s path change are obvious.The interannual change of northern limit for south wind in summer(June~August) along 100°～125°E(East Asia) has very important influence on the water vapor transportation,the northern limit for south wind moved southward causing the decreasing of the water vapor.The D-value of wind field in more or less precipitation years shows that the southwest windstream of west Pacific subtropical high affects the water vapour transportation over North China in summer;its southwestern air flow from South China Sea carries abundant water vapor to the North China,which brings large quantity of rainfall,and it has obviously rised wind and meridional circulation in averaged along 100°~120° E in North China in typical wet years,which is different in typical dry years.