东亚冬季风指数及其对东亚大气环流异常的表征

COMPARISON OF FOUR EAST ASIAN WINTER MONSOON INDICES

基于月平均NCEP/NCAR再分析资料、CMAP全球降水资料及中国台站降水和冷空气资料,首先概括了东亚冬季风环流系统的主要成员,并对基于这些环流系统定义的有代表性的4种东亚冬季风指数进行了比较分析。结果表明,4种指数具有比较一致的年际和年代际变化特征,相互间都为显著正相关,表明各指数都能较好地反映出其他环流系统成员的异常。功率谱分析结果显示,所有东亚冬季风指数均具有3—4年的年际变化周期和6.5年周期及9—15年的年代际变化周期。此外绝大部分指数在20世纪80年代之后都有线性减弱的趋势。所有季风指数都能够很好地反映“强(弱)冬季风年,低层西伯利亚高压偏强(弱),阿留申低压偏深(浅),副热带北风气流偏强(弱),东亚副热带地区气温偏低(高),中层东亚大槽偏深(浅)及高层副热带西风急流偏强(弱)”的基本特性。但各指数与冬季影响中国的冷空气次数间均无很好的对应关系。另外,绝大多数指数与东亚地区夏季降水也有较好的滞后关系,表明冬季风不仅对同期环流系统存在作用,而且还可能影响到夏季。

Monsoon circulation is an important component of the global circulation systems. Based on the monthly NCEP/NCAR 50-year reanalysis dataset in 1958 - 2003, the global gridded CPC Merged Analysis of Precipitation （CMAP） dataset in 1979- 2003 and the observed precipitation, temperature, and cold air activity frequencies at 160 stations in China in 1958 - 2003, the main members of the East Asian winter monsoon （EAWM） circulation systems are summarized in this paper, and four typical EAWM indices （EAWMI） reflecting the basic characteristics of the main member are calculated and compared, respectively. Results show that all four indices display similar interannual and interdecadal variation characteristics in the research periods, and are positively, significantly correlated each other at a confidence level of 99 %, indicating that each index is able to describe the anomaly pattern of the EAWM circulations. The power spectra of four EAWM indices reveal that the indices all pose the most predominant interannual period of 3 - 4 years, the secondary period of about 6.5 years, and the main interdecadal period of 9- 15 years. Besides, most of four indices have shown a significant decreasing trend since the 1980s. Results also indicate that in strong （weak） EAWM years, both the Siberian high and the upper-level subtropical westerly jet are stronger （weaker）, and the Aleutian low and the East Asia trough are deeper （shallower） than normal, thus favorable （unfavorable） for the dominance of more powerful northwesterly wind and lower temperature over the subtropical region of East Asia. However, none of four indices has good relationship with the frequency of cold air activities in winter in China. Besides, after strong （weak） EAWM, less （more） summer precipitation will be seen over the regions from the Yangtze River valley to southern Japan and more （less） summer precipitation from the South China Sea to the tropical western Pacific. Therefore, the EAWM also has a remarkable influence on the next summer monsoon.