全球海洋大气耦合环流模式中的ENSO特征对气候背景态改变的敏感性

文中利用一个高分辨率全球海-气耦合环流模式设计两组长期积分试验,揭示了在不同气候背景态下热带太平洋年际变化特征及模式ENSO循环控制机理的差异。通过分析海表温度、上层海洋热容量和低层风场异常的年际变化特征及其和赤道中东太平洋海表温度异常的关系,揭示了基于不同气候背景场的ENSO循环的不同演变过程。结果表明:ENSO年际变率特征(包括振幅、频率等)对气候背景态相当敏感,在不同的背景场下ENSO循环的控制模态可以明显不同。试验表明,当热带太平洋东冷西暖的背景热力梯度接近多年气候平均时,模式ENSO循环表现为所谓的“时滞振子”模态控制,而随着东西向背景热力梯度显著减小,ENSO循环则可以表现为驻波模态控制。研究结果为认识年代际背景变化影响年际ENSO循环的机理提供了一种启示。

SENSITIVITY OF ENSO CHARACTERISTICS IN A COUPLED OCEAN-ATMOSPHERE GCM TO CHANGE OF CLIMATOLOGICAL BACKGROUND STATE

Differences of characteristics of ENSO variability between two different climatological background states were investigated by means of two numerical experiments with a coupled ocean - atmosphere general circulation model. The analyses concerning interannual variabilities of the sea surface temperature, upper ocean heat content, and surface wind anomalies, as well as the relationship between these three variables and the eastern equatorial Pacific sea surface temperature anomaly, exhibit distinguishing processes of the ENSO cycle for different background states. It was found that the ENSO characters including the frequency and the amplitude and its controlling mechanism strongly depend on the climatological background states. Two different ENSO modes were identified for the two different background states. One is the "delayed oscillator" mode, corresponding to a background state close to the observation; and the other is a stationary mode, corresponding to a background state with a decreased zonal thermal gradient and a flat thermocline structure along the equatorial Pacific. Results presented in this study provide a clue to further understand the role of interdecadal variabilities played as a background state in the interannual variability of ENSO.