印度洋对ENSO事件的响应:观测与模拟

Indian Ocean Response to ENSO:Observation and Air-Sea Coupled Model Simulation

观测事实显示 ,在ElNi no期间 ,伴随着赤道中东太平洋表层海温 (SST)的升高 ,热带印度洋SST出现正距平。作者利用海气耦合模式模拟了印度洋对ENSO事件的上述响应 ,并进而讨论了其物理机制。所用模式为法国国家科研中心Pierre Simon Laplace全球环境科学联合实验室 (IPSL)发展的全球海气耦合模式。该模式成功地控制了气候漂移 ,能够合理再现印度洋的基本气候态。观测中与ENSO相关的热带印度洋SST变化 ,表现为全海盆一致的正距平 ,并且这种变化要滞后赤道中东太平洋SST变化大约一个季度 ,意味着它主要是对东太平洋SST强迫的一种遥响应 ,模式结果也支持这一机制 ,尽管模式中的南方涛动现象被夸大了 ,使得模拟的与ENSO相关联的SST正距平的位置南移 ,阿拉伯海和孟加拉湾被负距平 (而不是正距平 )所控制。研究表明 ,东太平洋主要通过大气桥影响潜热释放来影响印度洋SST变化。赤道东太平洋ElNi no事件的发展 ,导致印度洋上空风场异常自东而西传播 ;伴随着风场的变化 ,潜热发生相应变化 ,并最终导致SST异常的发生。非洲东海岸受索马里急流控制的海域 ,其SST的变化不能简单地利用热通量的变化来解释。证据显示 ,印度洋的增暖是ENSO事件发生的结果而不是其前期信号。

During El Nio events, when positive sea surface temperature (SST) anomalies form in the equatorial eastern Pacific, SST anomalies of same polarity also tend to develop in the tropical Indian Ocean This study attempts to model and explain the large scale features of the observed SST anomaly field in the Indian Ocean during El Nio years The IPSL (Institute Pierre Simon Laplace des Sciences de l'Environnement Global, France) air sea coupled model is used The model is successful in controlling climate drift, and has good performance in producing the Indian Ocean climatic states; examples are the seasonal variation of SST over the Arabian Sea and the effects of surface wind in producing seasonal SST change The observed ENSO related tropical Indian Ocean SST anomalies are spatially amorphous and have positive polarity throughout the domain This kind of Indian Ocean response follows the variation of eastern tropical Pacific SST with a time lag of about one season, indicating it is being mainly the effect rather than the cause of the original eastern Pacific forcing The model simulation supports this mechanism, though due to the exaggerated Southern Oscillation, the center of the ENSO related positive anomalies shifts southward, both the Arabian Sea and the Bay of Bengal are dominated by negative rather than positive anomalies It's found that the eastern Pacific forces the Indian Ocean mainly via latent heat release in the model The development of El Nio event in eastern equatorial Pacific results in the propagation of anomalous wind from the eastern Indian Ocean to the west Following the surface wind change, the corresponding latent heat flux change ultimately produces the SST anomalies Along the eastern coastline of South Africa where the robust Somali current dominates, the SST change cannot be explained simply in terms of the surface heat flux Notice that this study shows no confidence for the Indian Ocean warming as precursor of ENSO