春季南半球环状模与长江流域夏季降水的关系:Ⅱ 印度洋和南海海温的“海洋桥”作用

THE RELATIONSHIP BETWEEN THE SUMMER PRECIPITATION IN THE YANGTZE RIVER VALLEY AND THE BOREAL SPRING SOUTHERN HEMISPHERE ANNULAR MODE: Ⅱ THE ROLE OF THE INDIAN OCEAN AND SOUTH CHINA SEA AS AN “OCEANIC BRIDGE”

  • 摘要: 用回归、合成、相关、ESVD等方法分析了春夏季印度洋、南海海温异常在春季南半球环状模(SAM)与夏季长江中下游降水关系中的作用。研究发现春季南半球环状模指数(SAMI)正(负)异常时,同期南印度洋中高纬、北印度洋海域海温出现了明显正(负)异常,这种海温的正(负)异常在夏季依然存在,并且北印度洋的海温异常得到加强。对印度洋和南海海域详细划分区域后的进一步分析表明春季南半球热带外大气环流(SAM)异常可以强迫南印度洋中高纬海域海温发生明显异常。这种异常可以持续到夏季,而且表现出传播特性,即:南印度洋中高纬海温异常可以传播到北印度洋(包括阿拉伯海和孟加拉湾)和南海海域,加强这些海域的海温异常。对东亚夏季风与夏季海温关系的分析表明:东亚夏季风异常对应的夏季北印度洋、南海海温异常与春季SAM异常对应的夏季北印度洋、南海海温异常的形势相似,符号相反。说明印度洋、南海海温是春季SAM影响夏季长江中下游降水的一个“桥梁”。基本思路为:强(弱)春季SAM可以引起南印度洋中高纬海域海温的偏高(偏低);南印度洋中高纬海域偏高(偏低)的海温从春季持续到夏季并且传播到阿拉伯海、孟加拉湾、南海海域;这些海区偏高(偏低)的海温可以导致东亚夏季风减弱(加强),而东亚夏季风减弱(加强)是长江中下游降水偏多(偏少)的一种有利条件。

     

    Abstract: The role of SSTs in the Indian Ocean (IO) and South China Sea (SCS) in the relationship between the summer precipitation in the Yangtze River valley and the boreal spring Southern Hemisphere annular mode (SAM) was examined by applying regression, composite, correlation and extended singular value decomposition (ESVD). When the boreal spring Southern Hemisphere annular mode index (SAMI) is anomalous, significant SSTA occurs in the middle and high latitudes of South Indian Ocean (SIO) and North Indian Ocean (NIO), which may continue to the summer time and enhance in NIO. Based on the partition in the IO and SCS, the further analyses reveal the extratropical Southern Hemisphere atmospheric circulation anomalies (SAM) in the boreal spring may force SST and induce SSTA in the middle and high latitudes of SIO, which may continue to the summer. The anomalies may propagate from the middle and high latitudes of SIO to NIO (including the Arabian Sea and Bay of Bengal) and SCS and reinforce the SSTA in these regions. The study on relation between East Asian summer monsoon (EASM) and SST indicates that the summer SSTA in NIO according to EASM is similar to that according to the boreal spring SAM, but the signs are opposite. It indicates that the SSTA in the IO and SCS is a bridge between the boreal spring SAM and summer precipitation in the Yangtze River valley. The basic process is that the strong (weak) boreal spring SAM may lead to the high (low) SSTs in the middle and high latitudes in SIO, which propagate to the Arabian Sea, Bay of Bengal and SCS in which the high (low) SSTs conduce to the above (below) than normal summer precipitation in the Yangtze River valley by EASM.

     

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