2011年冬季长江流域气温持续偏低的可能成因探析

Exploration of possible causes for the low temperature throughout the winter of 2011 in Yangtze River basin

利用长江流域50个气象台站的气温资料、NCEP再分析资料和美国国家冰雪数据中心的北极海冰资料,分析了2011年冬季长江流域气温持续偏低的可能成因。结果表明,乌拉尔山阻塞高压和西伯利亚高压异常偏强及稳定维持,是长江流域冬季气温持续偏低的主要影响系统,其持续天数和强度均为1961年以来历史最大值。进一步分析表明,冬季乌山阻高和西伯利亚高压强度偏强和持续天数偏多易发生在La Nina年,500 hPa环流特征类似于La Nina年冬季平均环流条件;北极海冰面积异常偏小使冬季西伯利亚高压得到加强和乌山阻高持续。La Nina事件和北极海冰面积异常偏小是长江流域冬季气温持续偏低的重要外强迫因子。

Exploration of possible causes for the low temperature throughout the winter of 2011 in Yangtze River basin has been performed with the temperature data of 50 meteorological stations in the same basin,NCEP reanalysis datasets and arctic sea ice data from NSIDC.The results have shown both Siberian high and Ural blocking high which is abnormal intensified and stable continuance are main synoptic systems led to low temperature throughout the winter of 2011 in Yangtze River basin,whose intensity and lasting time all have reached to the maximum value since 1961.Further analysis indicate that the stronger intensity and more lasting time of Siberian high and Ural blocking high in winter appear easily in La Nina years,and the circulation features at 500 hPa are similar to mean circulation pattern in winter of La Nina years.Arctic sea ice area being abnormally smaller makes Siberian high strengthened and Ural blocking high lasted.La Nina and arctic sea ice area being abnormally smaller may act as the major external forcing factors causing air temperature to be continuously lower over Yangtze River basin.