一个新的季风指数及其年际变化和与雨量的关系  

A New Monsoon Index,Its Interannual Variability and Relation with Monsoon Precipitation

作　　者：李建平[1] 曾庆存[1] 

机构地区：[1]中国科学院大气物理研究所,北京100029

出　　处：《气候与环境研究》2005年第3期351-365,共15页Climatic and Environmental Research

基　　金：国家自然科学重点基金项目40233027;国家杰出青年科学基金项目40325015

摘　　要：作者按曾庆存等所定义的标准化风场季节变率(和利用新的资料重新作了计算,为与国外传统的和至今大多数学者的定义一致,取δ*=-δ2>0(即冬、夏风向差大于π/2)作为季风区,结果涵盖了迄今国内外所指出的全球所有季风区(但比曾庆存等算得的区域略为小些),尤其是热带季风区正处于冬季和夏季赤道幅合带(ITCZ)位置所夹的范围内。其后,用李建平和曾庆存建议的动态风场标准化季节变率δm*=δm-2(δm形式上与δ相似,但依赖于年份m)作为各年季风指数,计算了各主要季风区区域平均的δm*的年际变化,得到南亚夏季风和东亚夏季风自20世纪70年代中期起、南海夏季风自20世纪80年代起和西非夏季风自1967年起都有不同程度的长期减弱趋势,尤其以西非夏季风减弱最明显。西非夏季风指数和南亚夏季风指数与当地夏季雨量呈显著正相关,东亚夏季风指数与中国和东亚夏季雨量的空间分布有一定的统计相关结构,而南海夏季风指数则与全球各海区夏季降水和海平面气压异常有较好的大范围统计相关。The normalized seasonality of winds δ presented firstly by Zeng is calculated again by use of new datasets. To consist with the traditional and known definitions from many researchers, we take the region where δ^＊=δ-2〉0, i.e, the difference in wind direction between winter and summer is lager than π/2 as monsoon region. The geographical extent of the global monsoons form the method here covers all monsoon regions over the world known so far （however, the domain here is slightly smaller than that from Zeng）, especially the tropical monsoons are just included in the region between the positions of the Intertropical Convergence Zone or ITCZ in winter and summer. Then, the interannual variations of areal average δm^＊ of some key monsoons as the broad scale monsoon index proposed by Li and Zeng are analyzed by virtue of the dynamical normalized seasonality （DNS） of winds δm^＊=δm-2 （δm is similar to δ but depends on year m）. The long-term decreasing trends with different extent can be found in the intensities of the South Asian summer monsoon （SASM） and East Asian summer monsoon （EASM） since the mid- 1970s, the South China Sea summer monsoon （SCSSM） since 1980s, and the West African summer monsoon （WASM） since 1967, especially the most remarkably weakening in the WASM. Both the West African summer monsoon index （WASMI） and the South Asian summer monsoon index （SASMI） are significant positively correlated with the summer precipitation over the local monsoon regions, respectively, and there is statistical structure in the correlation map between the East Asian summer monsoon index （EASMI） and summer rainfall in China and East Asia, and there exist better statistical correlations over large regions in every Oceans between the South China Sea summer monsoon index （SCSSMI） and summer global rainfall and sea level pressure anomalies.

关 键 词：标准化季节变率 季风 季风指数 季风区 年际变化 

分 类 号：P434[天文地球—大气科学及气象学]