晋北地区夏季降水异常的时空分布及其环流特征分析

利用美国国家环境预报中心(NCEP)再分析资料以及晋北地区18个台站1960-2008年夏季降水资料,通过M-K突变曲线、滑动t检验、累积距平3种气候突变检验方法对晋北地区夏季降水的统计检验结果均表明,夏季降水在1996年发生了由多到少的转折。线性趋势法分析晋北地区夏季降水表明:夏季降水呈负的线性趋势,说明自1960年以来晋北地区夏季降水一直处在减少的趋势,干旱较为明显,尤其是广灵、平鲁、灵丘干旱趋势更为严重。对晋北夏季多雨、少雨年的大气环流异常特征进行了合成分析,结果表明:欧亚中高纬位势高度异常直接影响着晋北地区夏季降水的异常,多(少)雨年夏季500hPa位势高度呈现出"负(正)-正(负)-负(正)"的分布特征,中高纬地区以经(纬)向环流为主,冷空气活动频繁(偏弱),晋北地区处在槽(脊)的东南部,有利于降水偏多(少)。对流层低层流场多雨年西太平洋有暖湿气流向北输送,直达蒙古到东北一带与西伯利亚分裂下来的弱冷空气在华北地区相遇,有利于晋北地区夏季降水偏多。少雨年水汽条件差,不利于降水。

Temporal spatial features and circulation characteristics of summer precipitation in northern Shanxi

Based on NECP reanalysis data and the observational data from 18 stations in Northern Shanxi during 1960-2008,by using the linear trend analysis,M-K sudden change test,t-test and other methods,we analyzed the characteristics of the summer precipitation in the study area.Results showed that the summer precipitations in northern Shanxi have decreased since 1996.By analyzing the summer precipitation tendency,the result showed that the summer precipitations in northern China have decreased since 1960.The composite analysis of atmospheric circulation shows that the geopotential height in Eurasian middle-high latitudes correlated with the summer precipitation in northern Shanxi.In rainy years,the 500hPa geopotential height anomaly was positive,zonal circulation strengthened,and the cold air was active frequently.The situation in drought years was in opposite to that of rainy years.In addition,in rainy years the moisture transport from West Pacific met the cold air from Siberian,which was good for raining.