全球海洋环流模式中上层海洋对表面强迫的响应和调整 I. 年际变率

The upper-ocean response and adjustment to surface forcing in an ocean general circulation model

利用一个较高分辨率的全球海洋环流模式在COADS1945～1993年逐月平均资料的强迫下对海温和环流场进行了模拟试验,研究了全球热带海洋(主要是热带太平洋)海温和环流场的年际变化特征及模式ENSO冷暖事件演变的控制机理.结果表明,模式成功地再现了和观测一致的海温和环流的年际变化以及ENSO演变特征.其中热带印度洋年际SST变率的主要模态表现为与ENSO相联系的海盆尺度的一致性增暖或变冷现象,次级模态为热带印度洋偶极子模态;热带大西洋的SST年际变率表现为类ENSO的年际振荡现象.在热带太平洋,SST年际变化主要表现为ENSO型,环流的年际变率表现为与ENSO相对应的热带海洋质量循环圈的年际异常.对应于暖(冷)事件,前期赤道海洋垂直环流圈显示出减弱(增强)的特征.其中南赤道流异常的位相较Nino3区海温总体要超前5个月左右的时间;赤道上翻流异常的位相在表层要超前4个月,并随时间由上至下扩展;赤道潜流的异常则显示出东传特征,其中最早的较为显著的异常发生ENSO成熟前3个月180°附近.在模式ENSO冷暖事件的演变过程中,次表层海温异常沿赤道的东传起了关键作用,模式的ENSO模态主要表现为"时滞振子"模态.

Interannual variabilities of the temperature and circulation of global ocean, particularly of the tropical Pacific ocean, as well as the controlling mechanisms of ENSO evolution are investigated by a high resolution ocean general circulation model forced with COADS 1945～1993 monthly mean data. It was found that quite realistic interannual behaviors were reproduced well with the model. In the tropical Indian Ocean, the ENSO related basinwide warming/cooling mode and the dipole mode are successfully simulated. And the model also successfully simulates a ENSO-like mode of the SST variations in the tropical Atlantic on interannual time scale. In the tropical Pacific Ocean, the SST interannual variances are significantly dominated by ENSO variability, and the circulation also exhibits a mass cycle interannual anomalies associated with ENSO, i.e., the mass cycle tends to weaken/intensify several months before a warm/cold event, among which the phase of SEC anomaly leads Nino3 index to approximate 5 months. The equatorial upwelling firstly appears on the surface 4 months before the mature phase of ENSO and subsequently spreads to the deep, an eastern propagation of EUC anomaly was found near 180° with its phase leads Nino3 index to 3 months. The eastern propagation of subsurface ocean temperature anomalies along equator was found closely related to the evolution of ENSO cycle, the 'delayed oscillator' mode is the controlling mode of the model ENSO events.