【摘要】 华北地区夏季降水在20世纪70年代中期以后进入年代际偏少阶段,表现出明显的干旱化趋势。华北干旱加剧具有特殊的大气环流背景,主要表现为在20世纪70年代中期以后亚洲大陆东部的热低压减弱,同时对流层低层到高层东亚夏季风环流减弱。这种异常的大气环流背景主要是由海陆热力差异和北极涛动的年代际变化造成的。近二十几年来,北极涛动维持在高指数位相是导致东亚地区大气环流异常的重要原因,并由此造成了华北干旱的加剧。更多还原

【Abstract】 The summer rainfall in North China has entered a decadal decreasing stage sincethe middle of 1970′s,which occurrences the considerbly droughtytrend.The aridization trend in North Chinahappensagainst a special background of atmospheric circulation.It is characterized by weaker heat lowover East Asia and the weakerEast Asian summermonsoon circulation after the middle- 1970′s.This kind of anomalous atmospheric circulation is mainly caused byinterdecadal variations of Arctic Oscillation(AO)and land-sea thermal contrast.AO always keeps at highindexphase during the recent two decades.It plays an important role inthe anomaly of atmospheric circulationof East Asia and finally cases the droughtyexasperation in North China.更多还原