El Nio事件大气-洋流异常与暖海温传播机理研究

A Study of Anomalous Atmosphere-Ocean Currents and the Propagation Mechanism for Warm Signal of Sea Temperature during El Nio Events

利用1971~2000年逐月SODA（SimpleOceanDataAssimilation）同化资料（Carton等，2004）、1980~2000年逐月NCEP／NCAR再分析资料（Kalnay等，1996）探讨中部型（暖海水首先出现在120°W以西）和东部型（暖海水首先出现在120°W以东）E1Nifio事件赤道纬向风应力及洋流的异常变化与暖海水信号的传播特征。研究指出：（1）中部型和东部型E1Nino事件发生时，太平洋上赤道海表最大西风应力距平在西太平洋地区都有显著的东传现象，但中部型E1N盗。事件西风应力距平强度强，造成西太平洋赤道表层的东向流可达东太平洋地区，这类E1Nino事件强度偏强。（2）中部型E1Nino事件，赤道表层洋流辐合区及其下沉运动由西太平洋向东太平洋传播，辐合下沉运动抑制了深层冷海水上翻，西太平洋暖水能够传到东太平洋与西太平洋赤道表层洋流辐合区及其下沉运动的东移有关。（3）东部型E1Nino事件西太平洋赤道表层洋流辐合区及其下沉运动没能直接传到东太平洋地区，东太平洋暖水形成与局地（120°W以东）辐合下沉运动抑制深层冷海水上翻有关；东部型E1Nino事件暖池次表层的暖水，不是沿着西太平洋赤道次表层向东传播到东太平洋地区，而是由南太平洋西边界流将暖池海水带到40°S左右的西风漂流区，再由西风漂流平流到东太平洋。

Because of the sparse observation over the ocean, the important problems about the characteristics of the ocean currents and their relationship with the sea temperature anomaly during E1 Nino events are still not completely resolved, although there already have been a few researchers focused their attentions on this field. In order to deeply investigate the truth behind the puzzles in a new way, this research is based upon the Simple Ocean Data Assimilation （SODA） dataset from 1971 to 2000 and the NCEP/NCAR reanalysis dataset from 1980 to 2000, which are of high resolution and long time scale. Therefore, from the departures point of view, the variations of zonal wind and ocean currents as well as the propagation features of the sea temperature signal during E1 Nino events have been investigated by composite analysis. In this research, special emphasis is placed on the two main types of E1 Nino events： the middle-pattern E1 Nino and the east-pattern E1 Nino. According to the amplitude of the sea surface temperature anomaly and its characteristics of propagation, the middle-pattern E1 Nino event is the composite of 1982/ 1983, 1991/1992 and 1997/1998 events and the east-pattern E1 Nino event is the composite of 1972/1973 and 1976/ 1977 events. The results show that： （1） In the middle-pattern E1 Nino event （the anomalous warm water appears first to the west of 120°W） and the east-pattern E1 Nino event （the anomalous warm water appears first to the east of 120°W）, there is a significantly eastward propagation of the strongest western wind anomalies over the western equatorial Pacific Ocean. Besides, the positive （negative） equatorial surface current anomalies are associated with the enhanced （weakened） western wind anomalies. The response of the ocean currents to the zonal wind anomaly has a high correlation with the intensity and the propagation characteristics of the zonal wind anomaly. In the middle-pattern E1 Nino event, the western wind anomalies are relatively strong, which is favorable for the eastward movement of the positive equatorial surface current anomalies over the western Pacific. Therefore, the intensity of such a E1 Nino event is relatively strong. （2） In the middle-pattern E1 Nino event, over the western Pacific, the anomalous downwelling of the equatorial ocean currents caused by the convergence of surface zonal ocean current anomalies suppresses the uprush of the deep cold water, leading to the warm surface water, which also moves eastward with the eastward propagation of the anomalous downwelling. （3） In the east-pattern E1 Nino event, the anomalous downwelling of the equatorial ocean currents caused by the convergence of surface zonal currents anomalies over the western Pacific Ocean does not move eastward, and the formation of warm water is relevant to the regional （east of 120°W） anomalous downwelling of the equatorial ocean currents caused by the convergence of surface zonal ocean current anomalies, which suppresses the uprush of the deep cold water. This is considerably different from the feature in the middle pattern E1 Nino event. Besides, based on the analysis of the propagation of the sea surface temperature and ocean currents over the southern Pacific, it is found that the path along which the warm water propagates eastward may be the westerly drift region rather than the climatic equatorial thermal-cline.