中纬度阻塞高压指数与华北夏季降水的联系

Association of Mid-latitude Blocking High Index with Summer Precipitation in North China

摘要:

利用500hPa高度场资料计算了亚洲中纬度3个区域(鄂霍次克海区、贝加尔湖区、乌拉尔山区)阻塞高压指数,通过相关分析、合成分析研究了阻塞高压指数与华北夏季降水之间的联系。结果表明3个区域阻塞高压指数均具有明显的年代际变化,并且与华北夏季降水在年代际尺度上关系密切,相关系数分别为-0.4622、-0.6763、-0.6713。在阻塞高压的频发期,中纬度西风在东亚地区发生分支,分别形成极锋和副热带锋区,东亚夏季风偏弱,西太平洋副热带高压位置偏南,我国夏季雨带位置偏南,造成华北夏季干旱;而在阻塞高压的少发期则相反。

关键词:阻塞高压;华北;降水;年代际变化

Abstract:

Based on summer 500hPa geo-potential high fields,mid-latitude blocking high indexes of three areas (Okhotsk Sea,Baikal Lake,Ural Mountains) in Asia are calculated in this paper and the relation between blocking high indexes and summer precipitation in North China is investigated by means of correlation and composite analysis.Results show that the blocking high indexes of the three areas all have distinct inter-decadal variations,and are close related with summer precipitation in North China on inter-decadal time scales,with correlation coefficents being -0.4622,-0.6763 and -0.6713,respectively.When the Asian mid-latitude blocking high occurs frequently,the mid-latitude westerly turns into two branches,forming polar and sub-tropical fronts,and the East Asian summer monsoon is weaker than normal,the sub-tropical high lies south of normal position,and the summer rain-belt lies south of normal,resulting in summer drought in North China.It is vice versa if the Asian mid-latitude blocking high occurs infrequently.

Key words:blocking high;North China;precipitation;inter-decadal variation