季节背景对ENSO循环过程中SSTA增/减幅作用的数值试验研究

IMPACT OF SEASONALITY IN BOTH THE ATMOSPHERE AND OCEAN ON VARIABILITIES IN SSTA

利用热带太平洋地区 2层区域海洋模式和再分析资料探讨了大气 /海洋的季节背景对ENSO时间尺度上海温异常的增幅或减幅作用。结果表明 :不论什么季节背景下 ,就海洋变化而言 ,El Nino/La Nina事件均可存在 ,说明 El Nino/La Nina事件的存在和维持并没有季节性选择 ;模式海洋的西太平洋赤道地区次表层海水温度异常变化位相明显超前于东太平洋SSTA且在空间上自西向东传播 ,同时有位相超前的量还包括模式第 1层厚度异常及热容量异常 ,这些对 ENSO的预测和机制研究具有重要意义。 SSTA的振幅在不同的季节背景下可受到不同的调节。以春季为背景 ,同样的异常风应力作用于海洋 ,可使 NINO3区 SSTA较正常季节背景下该区的 SSTA振幅明显增大 ;而在冬季背景下可使 SSTA受到一定程度的减幅 ,这说明 El Nino/L a Nina现象的发生和消亡有季节选择倾向。与春季背景下 NINO 3区SSTA的增幅倾向相反 ,模式第 1层厚度异常的振幅则受到削弱。而西太平洋赤道地区 ,模式海洋混合层的厚度异常则有所增强。这种与 SSTA增

An intermediate ocean model for tropical Pacific is employed to investigate the influences of the different seasonal background on the variations of the sea surface temperature anomalies on ENSO time scale. The control experiment has been carried out, in which the ocean is driven by an anomalous wind-stress fields that involve the seasonal cycle. The sensitivity experiments are conducted, in which the ocean is forced by the same wind-stress anomalies but under a background of a special season such as spring. It is found that El Nio/La Nina events do appear in any season, which indicating that the existence and maintenance of El Nio/La Nina does not depend on seasons. In equatorial western Pacific in the model, the disturbances of subsurface temperature that propagates eastward are evidently leading in phase to the SSTA of eastern Pacific.This is useful for us to understand the mechanism of ENSO cycle and to improve ENSO predictions. The amplitudes of SSTA are different under different seasonal backgrounds. The SSTA in NINO3 region during boreal spring (winter) as the climate background case is obviously bigger (smaller) than that of control case. Further, if the SSTA in winter season is not big enough, the El Nio/La Nina event will disappear because the winter season background tends to reduce the magnitude of SST anomalies.