近50a来华北地区负积温变化特征

利用华北地区62个气象站1961-2008年冬季日平均气温资料和NCEP／NCAR再分析资料，运用经验正交函数分解（empirical orthogonal function，EOF）、旋转经验正交函数分解（rotated em—pirical orthogonal function，REOF）、Morlet小波和合成分析等方法，分析了华北地区负积温变化特征及同期环流背景场的变化特征。结果表明，1）华北负积温具有全区一致性增加的特点，其中山西北部增加明显。2）由于华北地区东部和西部负积温增长幅度不同，可将华北地区分为2个区域。两区负积温均有突变，其中Ⅰ区负积温的突变年份为1988年，Ⅱ区负积温的突变年份为1986年，Ⅰ区负积温存在3～6a周期振荡，Ⅱ区负积温存在2～4a周期振荡。3）北半球冬季环流场的变化与华北负积温异常有一定相关关系。合成分析的结果表明，在近地面层，偏冷年西伯利亚高压偏强，华北冬季偏冷，负积温绝对值偏大；在对流层中层，东亚大槽及乌拉尔山高压脊为主要影响系统，东亚大槽较深、乌拉尔山脊偏强，冷空气活动偏强；偏暖年则反之。

Characteristics of the negative accumulated temperature change in North China in recent 50 years

Based on the observed daily temperature data from 62 stations in North China and NCEP/ NCAR reanalysis data from 1961 to 2008, the characteristics of negative accumulated temperature （NAT） change in North China and its circulation background were studied through methods such as EOF, REOF, and wavelet analysis. Results show that： 1 ） the NAT in North China increased consistent- ly, especially in Northern Shanxi Province ;2） The NAT in North China can be divided into two subdi- visions because the NAT increasing amplitudes were different in east and west. There were both abrupt changes in the west and east of North China, occurring in 1988 and 1986 respectively. A 3-6 years＇ cycle period was found in the west of North China while it was 2---4 years in the east of North China; 3 ） Changes of Northern Hemisphere winter atmospheric circulation had a close relation with the NAT anomalies in North China. Further composite analysis showed that cold periods were represented by stronger Siberian High, colder winter in North China and larger NAT＇ s absolute value near the ground while the main influence systems were the East Asian trough and Ural ridge in the middle troposphere.The stronger Ural ridge and the deeper East Asia trough made the cold air activity stronger in North China. In warm periods, it was the opposite situation.