热带大气季节内振荡激发El Nino的机制

EXCITING MECHANISM OF TROPICAL INTRASEASONAL OSCILLATION FOR EL NINO EVENT

关键词:  热带季节内振荡  年际异常  El Nino

Key words:  Tropical intraseasonal oscillation  Interannual anomaly  El Nino

摘要:

资料分析表明,热带大气季节内振荡同El Nino的发生有密切的关系。在El Nino事件发生之前,热带大气(尤其是赤道西太平洋地区)季节内振荡异常加强;伴随着El Nino的发生,热带大气季节内振荡动能明显减弱,而准定常系统动能明显增强。简单海-气耦合模式的分析表明,只有在年际时间尺度大气外强迫作用下,海-气系统才可以产生类似ENSO模的耦合波。资料和理论模式分析的结果相结合,说明热带大气季节内振荡激发El Nino的机制是:热带大气季节内振荡的年际异常通过海-气相互作用而对El Nino事件起重要的激发作用。

Abstract:

The interaction between tropical intraseasonal oscillation(ISO) and El Nino has been paid more attentions.But El Nino events just occur after an interval of several years,which is different from that tropical intraseasonal oscillations always exist in the atmosphere.Therefore,it is important to know how tropical intraseasonal oscillation excite the El Nino event.The data analyses show that not only the kinetic energy of tropical ISO decreases abruptly in association with the occurrence of El Nino,but also that the interannual anomalous variation of tropical ISO intensity is closely related to El Nino event.These mean that the tropical intraseasonal oscillation plays an important role in exciting El Nino through its interannual anomalous variation.A simple air-sea coupled model study shows that the periodical self-excited oscillation can be produced in air sea coupled system,but the pattern is different from ENSO mode.When there is external (atmospheric)forcing with interannual time scale,a coupled mode which likes ENSO mode will be excited in the air-sea coupled system.Therefore,the dynamical analysis has consistent result with the data nanlyses:The interannual anomalies of intraseasonal oscillation in the tropical atmosphere play an important role in exciting El Nino event.