华北夏季旱涝的环流特征分析

本文运用月降水量、500hPa、100hPa月平均高度场和海平面气压场，在对50a华北夏季旱涝等级重新评定的基础上，分析了与华北夏季旱涝年对应的环流异常特征。结果表明华北旱涝年，对应整个北半球上各层都存在显著的环流异常变化。旱年500hPa环流异常使得极涡偏心，相应乌拉尔山和北美的气候槽偏强；中纬度位于华北的平均槽东移到朝鲜日本一带，而西部脊东移控制华北；低纬西太平洋副高偏东，印度低压槽偏弱。涝年则相反。在海平面气压场上，除了在与高层对应的显著异常区有相应变化外，在我国东部大陆大部及赤道中东太平洋上也有一显著的异常区，证实夏季风和KNSO与华北旱涝存在密切的联系。在100hPa高度场旱涝年环流差异主要表现为南亚高压南北界的位置变化。

AN INVESTIGATION ON ATMOSPHERIC CIRCULATION ANOMALY OF FLOODS/DROUGHTS OVER NORTH CHINA

Based on 1951-2000 summer flood/drought severity graded by a new scheme, atmospheric circulation characteristics associated with floods/droughts over North China are addressed in terms of monthly rainfall, 100hPa, 500hPa height fields and sea level pressure data from NCC. Evidences suggest that prominent anomalies occur over Northern Hemisphere with the fact that the polar eddy partially locates over western Siberia and North America indicative of deeper than normal land troughs, and on a local basis the normal ridge and trough shift eastward over North China and Korea respectively while at lower latitudes presented are a weaker Indian trough, stronger North African High and eastward shifting West Pacific subtropical high. And in sea surface pressure maps, prominent anomalies are present over most part of East China and the tropics of east Pacific apart from those counterparts at mid-troposphere denoting possible linkage to summer monsoon and ENSO. While the location variation of South-Asian high at 100hPa level is also related to the floods/droughts over North China.