一个改进的混合型海气耦合模式：ENSO模拟

通过在中国科学院大气物理研究所热带太平洋环流模式与一个统计大气模式所建立的混合型海气耦合模式中引入次表层上卷海温非局地参数化方案, 对比分析了次表层上卷海温对耦合模式模拟结果的影响, 表明在引入次表层上卷海温非局地参数化方案前耦合模式模拟的SSTA最大变率中心位于日界线附近赤道南北狭窄范围内, 而在赤道东太平洋及南美沿岸一带变率过低, 周期呈准2年振荡。改进后, 耦合模式模拟结果的分布不论在东西方向亦或南北方向与观测更为相近, 振荡周期为4年左右, 而且还能模拟出观测中ENSO振荡的季节依赖性特征。进一步分析改进的耦合模式中海气耦合特征, 表明 “延迟振子” 理论、 “西太平洋振子” 理论、 “充电-放电振子” 理论及 “平流-反射” 理论所揭示的一些规律在该模式中都能被不同程度地描述出来, 这说明在实际的ENSO循环过程中, 可能有多种机制在同时起作用。

An Improved Hybrid Coupled Model: ENSO Simulations

In this study, an improved hybrid coupled model (hereafter referred to as “HCM_emd”) is developed by parameterizing empirically the temperature of subsurface water entrained into the mixed layer (Te), in which a tropical Pacific OGCM is coupled with a statistical atmospheric wind stress anomaly model that is constructed from a singular value decomposition (SVD) analysis through a SSTA submodel where Te is estimated empirically by means of the statistical relation with the sea level anomalies (SLA) simulated by the OGCM. As a comparison, a standard hybrid coupled model is also set up (hereafter referred to as “HCM_std”), in which the same OGCM and statistical atmospheric model are coupled directly. The long time free integrations show that there are many biases in the simulated interannual variability in HCM_std, which are observed in many other coupled models, such as the strong SST anomalies confined in a narrow band of the equator around the date line, but too weak anomalies in the eastern equatorial Pacific and along the coast of South America with a higher frequency oscillation (quasi-biennial oscillation). In contrast, HCM_emd performs much better. The simulated ENSO variability distributes much more realistically in both longitude and latitude directions with a frequency of 4 years, which is much closer to the observation. In particular, the seasonal phase-locked ENSO phenomenon is also reproduced in this improved coupled model. The further analysis shows that the simulated ENSO in HCM_emd is consistent to a certain extent with the delayed oscillator, western Pacific oscillator, recharge-discharge oscillator and advective-reflective oscillator from different aspects, implying that multi-mechanisms may operate at the same time during ENSO cycles.