1990年代中期南海季风系统年代际转型模态的时空特征

SPATIAL AND TEMPORAL CHARACTERISTICS OF DECADAL SHIFT IN THE MID-1990s OF THE SOUTH CHINA SEA SUMMER MONSOON

利用1979--2007年的CMAP降水、HadlSST的海表面温度数据和NCEP的850hPa风场数据，应用多变量联合季节经验正交分解（MY—SEOF）方法，研究了南海季风系统的前两个主模态特征，发现一个模态是厄尔尼诺／南方涛动（ENSO）模态，一个是在1990年代中期的年代际转型模态。区域敏感性试验发现南海季风系统的1990年代中期的年代际转型在去除南海热带区域（105～125°E，5-25°N）的范围内是最显著的，年代际转型模态出现在MV-SEOF的第一模态中，且主要体现在“季风年”季节循环顺序的MV．SEOF中；而变换其它纬度和经度以及非“季风年”季节循环顺序时，ENSO模态出现在第一模态中，同时年代际转型信号都会减弱并出现在第二模态中。南海季风系统的年代际转型反映了南海局地季风型海．气耦合系统的特征，其中南海局地海表面温度（SST）的年代际变化表现出对全球变暖的响应特征，而南海局地的海．气耦合作用则起到了“放大器”的作用，使南海中北部SST的年代际信号强化并影响到整个季风系统中。

Decadal climate shift in the mid-1990s over the South China Sea summer monsoon （SCSSM） was analyzed using monthly precipitation data from the CPC Merged Analysis of Precipitation （CMAP）, sea surface temperature data of Hadley Center and 850 hPa zonal wind data of NCEP-NCAR for the period of 1979--2007. A multi-variable season-dependent Empirical Orthogonal Function （MV-SEOF） was used to capture major modes of the SCSSM. It is indicated that one leading mode is the ENSO mode. The other one is a decadal change mode in the middle of 1990s. It is exhibited in the regional sensitive experiment that the decadal shift in the mid-1990s is the most significant one in the area of （5-25°N, 105-125°E） when the tropical area of the South China Sea is neglected. The decadal change mode is the first leading mode of MV-SEOF in the ＂monsoon-year＂ seasonal cycle. When the area or the seasonal sequence varies, the ENSO mode becomes the first mode while the decadal change mode weakens and appears in the second mode. The decadal change of the SCSSM reflects the ocean-atmosphere coupled characteristics of local South China Sea monsoon, which acts as an ＂amplifier＂ to strengthen the decadal signal of the central and northern South China sea SST and impacts the whole monsoon system.