High Circumfluence Characters in Spring-rainy Year and Drought Year in Northwest of China
西北地区春季多雨与少雨年的高空环流特征

Based on the spring precipitation data of 1961-2000 recorded at 119 meteorological stations in northwest of China,it has been analyzed for its space-time change,its 500 hPa high field and OLR distribution as well as 700 hPa wind field and specific humidity distribution in spring-rainy year and drought year.In rainy year,the 500 hPa high-field over middle latitude is positive in east and negative in west,the East Asian Low is weak and the Europe Low is strong;the 700 hPa vector wind is divergence field in areas of Africa-Europe,Siberia Sea and Philippine Sea Basin,and convergence field in areas of India and North China;the specific humidity field in North Hemisphere distributes in areas of Arabia Sea to Bengal Bay and the Yangtse River Basin;the main negative OLR anomaly centers locate in southeast seaboard,Bengal Bay and northwest regions,and the main positive in western Pacific Ocean.In drought year,the 500 hPa high-field is positive in west and negative in east,the high-pressure ridge from Mid-Asia to Xinjiang of China and the East-Asian trough are all strong;the 700 hPa vector wind is divergence field in northwest China and convergence field in areas of Europe,western Siberia and Tailand;the 700 hPa positive specific humidity field centers distribute in areas Bengal Bay and Philippine Sea Basin;the main negative OLR anomaly centers locate in areas from southeast seaboard to northern Tibet Plateau to northern Xinjiang,and the main positive in western Pacific Ocean and also in northwest China.