前期夏季西太平洋暖池热含量对江南春雨的影响及其可能机理

利用GODAS海洋温度资料、中国753站逐日降水资料以及NCEP/NCAR逐日再分析资料讨论了前期夏季西太平洋暖池热含量异常对江南春雨的影响,并通过高低层环流异常解释了其可能过程和机制。研究结果表明:(1)前期夏季暖池区热含量影响春雨的敏感海区位于9°~16°N,150°~166°E,与春雨强度呈显著反相关,前期夏季关键区热含量的显著偏低是春雨异常偏多的强信号。(2)多雨年和少雨年大气环流差值场与夏季暖池热含量(取反号)回归的次年春季大气环流形态基本一致。低层菲律宾海异常反气旋西北侧的暖湿西南气流输送及江南地区高层辐散抽吸运动是造成春雨偏多的直接原因。(3)关键区热含量在前期夏季的异常偏低使低层异常反气旋在其西北侧触发生成,并在菲律宾海附近持续存在(前夏至当年春季),春季引导强盛的西南气流向江南输送水汽;同时,热含量异常偏低在我国大陆东部激发出高层异常气旋并持续维持(前秋至当年春季),导致春季西风急流轴异常南压,高层形成异常辐散中心,形成强烈的抽吸作用,导致江南春雨显著偏多。前夏热含量显著偏高引起江南春雨偏少的过程则与之相反。

Impact of the preceding-summer heat content over western Pacific warm pool on Spring Persistent Rain and its possible mechanism

In this paper, the impact of the preceding-summer heat content over western Pacific warm pool on Spring Persistent Rain was analyzed based on the GODAS monthly mean sea temperature, China 753 stations precipitation and NCEP/NCAR daily reanalysis data. Possible process and mechanism were studied through anomalous circulation in upper and low level. Major results were: (1) Heat content over key region(9°~16°N,150°~166°E) in preceding-summer was anti-correlated with the intensity of SPR. The significant low heat content in preceding-summer strongly indicated surplus rainfall in spring. (2)Difference field (rainy years minus drought years) in spring was consistent with spring circulation regressed by the heat content(opposite sign) in preceding-summer over warm pool. Direct causes of surplus rainfall were warm and wet southwest airflow in the low level, which located in northwest of the anomalous Philippine Sea anticyclone, and the pumping effect over Jiang Nan in upper level. (3)The anomalous low heat content over key region in preceding-summer induced low-level anomalous anticyclone in northwest, which persisted to current spring from preceding-summer. In spring, driven by the anomalous anticyclone, powerful southwest flow carried abundant moisture to Jiang Nan. Meanwhile, anomalous cyclone of upper level over mainland of China was stimulated and lasted from preceding-autumn to current spring. The anomalous cyclone led to southward replacement of westerly jet axis and formation of the abnormal divergence center with intense pumping effect in the upper level, hence resulting in surplus rainfall in spring. Process of abnormally less rainfall in spring caused by anomalous high heat content in pre-summer was on the contrary.