积雪在El Ni(n)o影响东亚夏季气候异常中的作用

摘要

本文利用1948-2010年Global Land Data Assimilation System(GLDAS) NOAH陆面模式资料、GPCC月平均降水资料和NCAR/NCEP全球月平均再分析资料,采用滤波、距平合成和线性相关等方法,分析了El Ni(n)o成熟位相冬季欧亚大陆积雪异常的分布特征,研究了关键区积雪融化对后期春、夏季土壤湿度、土壤温度以及大气环流与降水的影响,揭示了El Ni(n)o事件通过关键区积雪储存其强迫信号并影响东亚夏季气候异常的机制和过程.主要结论如下:El Ni(n)o成熟阶段冬季伊朗高原、巴尔喀什湖东北部和青藏高原南麓区域是雪深异常的三个关键区,这些区域的雪深、雪融和土壤湿度有明显的正相关;这三个关键区雪深异常通过春季融雪将冬季El Ni(n)o信号传递给春、夏季局地土壤湿度,通过减少感热通量和增加潜热通量对大气环流产生影响;春末夏初伊朗高原土壤湿度异常对东亚夏季气候异常的影响最大,其引起的降水异常与El Ni(n)o次年夏季降水异常分布基本一致,春夏季青藏高原南麓和巴尔喀什湖附近土壤湿度也都明显增加,均会对中国华北降水增加有显著正贡献.总之,在利用El Ni(n)o事件研究和预测东亚夏季气候异常时,还应考虑关键区雪深异常对El Ni(n)o信号的存储和调制作用.%Utilizing the datasets of Global Land Data Assimilation System (GLDAS) NOAH land surface model,GPCC monthly mean rainfall and NCAR/NCEP global monthly mean reanalysis from 1948 to 2010,and the methods of filtering,composite and linear correlation,the characteristics of Eurasian snow depth anomalies in El Ni(n)o mature winter,its influences on soil moisture after snow melting,and finally on East Asian summer monsoon are investigated,and the main conclusions are as follows:In El Ni(n)o mature winter,the snow depths in regions of Iranian Plateau,northeast of Balkhash Lake,and south of Tibetan Plateau increase remarkably,so are the related snow melting and soil moisture.The above-mentioned three regions are identified as the key regions for snow depth to store and extend the El Ni(n)o signals.In spring,the snow begins to melt,and the soil moisture increases correspondingly,thus the El Ni(n)o signals are transmitted from winter snow depth to soil moisture in spring.As a result,sensible heat flux decreases and latent heat flux increases,and the atmospheric circulations are greatly influenced.The anomalous soil moisture in the Iranian Plateau is most important for the East Asian summer monsoon in El Ni(n)o decaying summer,since it has similar impact pattern on the anomalous summer precipitation as the El Ni(n)o composite.The spring and summer soil moisture in both the south of Tibetan Plateau and the northeast of Balkhash Lake increase simultaneously,which significantly contribute to the increased precipitation in North China.Therefore,to investigate and predict the East Asian summer monsoon variabilities by using El Ni(n)o signal,the roles of snow depth in storing and modulating El Ni(n)o impacts in those key regions should be considered.