影响南海夏季风爆发年际变化的关键海区及机制初探

THE KEY OCEANIC REGIONS AFFECTING INTERANNUAL VARIATION OF ONSET DATE OF SCSSM AND THEIR PRELIMINARY MECHANISMS

利用1958—2011年NCEP/NCAR再分析资料和ERSST资料,采用Lanczos时间滤波器、相关分析、回归分析、合成分析和交叉检验等方法,研究了影响南海夏季风爆发年际变化的关键海区海温异常的来源与可能机制。结果表明,前冬(12—2月)热带西南印度洋和热带西北太平洋是影响南海夏季风爆发年际变化的关键海区。冬季热带西南印度洋(热带西北太平洋)的异常增暖是由前一年夏季El Ni?o早爆发(强印度季风异常驱动的行星尺度东-西向环流)触发、热带印度洋(西北太平洋)局地海气正反馈过程引起并维持到春季。冬季热带西北太平洋反气旋性环流(气旋性环流)及印度洋(热带西北太平洋)的暖海区局地海气相互作用使得印度洋(热带西北太平洋)海温异常维持到春末。春季,逐渐加强北移到10°N附近的低层大气对北印度洋(热带西北太平洋)暖海温异常响应的东风急流(异常西风)及南海-热带西北太平洋维持的反气旋性环流(气旋性环流)异常,使得南海夏季风晚(早)爆发。

The origin of SSTA of key oceanic regions affecting the interannual variation of onset date of South China Sea summer monsoon and possible mechanisms are studied using Lanczos filter, correlation analysis, regression analysis, composite analysis and cross-validation with NCEP/NCAR reanalysis dataset and ERSST dataset from 1958 to 2011. The results show that the previous winter tropical southwest Indian Ocean and tropical northwest Pacific are key oceanic regions affecting the interannual variation of South China Sea summer monsoon onset date. The anomalous warming of winter tropical southwest Indian Ocean （tropical northwest Pacific） is triggered by E1 Ni-o early onset （planetary east-west circulation induced by heating of strong Indian summer monsoon）, and maintained by local air-sea interaction positive feedback process in tropical Indian Ocean （tropical northwest Pacific） until the spring. The winter anticyclonic （cyclonic） circulation over tropical northwest Pacific and local air-sea interaction positive feedback process in tropical Indian Ocean （tropical northwest Pacific） make SSTA in tropical Indian Ocean （tropical northwest Pacific） maintain until the spring. The spring low-level easterly jet （anomalous westerly） responding to warm SSTA in north Indian Ocean （tropical northwest Pacific） gradually enhances and moves northward to 10°N. The anomalous anticyclonic （cyclonic） circulation over South China Sea and tropical northwest Pacific induces late （early） onset of South China Sea summer monsoon.