北半球冬季纬向平均环流的结构及对我国气候的影响

Structure of the Zonal-Mean Circulation Over the Northern Hemisphere and Its Impact on Climate of China in Winter

冬季对流层纬圈平均纬向风 (u)最主要的模态表现为两个相反符号的极值中心 ,一个在 30°～ 35°N之间 ,另一个则在 5 5°N。与此相联系的纬圈平均高度场最突出的模态也是有两个相反符号的中心 ,一个在 40°N附近 ,另外一个则在 6 5°N附近。因此 40°N和 6 5°N纬圈平均位势高度的差可以很好定义西风指数。西风环流的强弱不仅对北半球的气候有显著影响 ,对我国冬季的气温和降水也有显著关系。在高指数环流盛行的年份 ,我国普遍气温偏高。 16 0个站平均气温与西风指数的相关系数达到 0 .6 3。同时华北及以南降水增加 ,其中黄土高原、关中平原及以东地区相关最显著。 16 0站平均降水量与西风指数的相关达 0 .38。高指数年份里 ,西伯利亚高压和东亚大槽都减弱 ,低指数年份则增强 。

As revealed by the empirical orthogonal function analysis (EOF), the dominant modes of northern hemispheric zonally mean wind ( u ) in winter show two centers of opposite sign, one center located near 30°-35°N and another near 55°N The prominent modes of geopotential heights also show two centers, one is at 40°N and another at 65°N These two modes connected tightly So, the zonal index can be defined as the difference in geopotential height between 40°N and 65°N This kind of zonal index correlate with westerly of 55°N at 0 96 The anomalous variation of the westerly can impact the winter surface temperature and precipitation of China significantly During the high index years, most of China become warmer, and the precipitation in the mid eastern China will increase Correlation between the zonal index and the 160 station mean temperature and precipitation is 0 63 and 0 38 respectively The Siberia High and Eastern Asia Trough that show the powerful control of winter climate of China, usually become weak during the high zonal index years