On the Mechanism of the Locking of the El Nino Event Onset Phase to Boreal Spring

The mechanism of the locking of the E1 Nino event onset phase to boreal spring （from April to June） in an intermediate coupled ocean-atmosphere model is investigated. The results show that the seasonal variation of the zonal wind anomaly over the equatorial Pacific associated with the seasonal variation of the ITCZ is the mechanism of the locking in the model. From January to March of the E1 Nino year, the western wind anomaly over the western equatorial Pacific can excite the downwelling Kelvin wave that propagates eastward to the eastern and middle Pacific by April to June. From April to December of the year before the E1 Nifio year, the eastern wind anomaly over the equatorial Pacific forces the downwelling Rossby waves that modulate the ENSO cycle. The modulation and the reflection at the western boundary modulate the time of the transition from the cool to the warm phase to September of the year before the E1 Nifio year and cause the strongest downwelling Kelvin wave from the reflected Rossby waves at the western boundary to arrive in the middle and eastern equatorial Pacific by April to June of the E1 Nino year. The superposition of these two kinds of downwelling Kelvin waves causes the El Nino event to tend to occur from April to June.

热带大气季节内振荡的几个基本问题

在一系列资料分析、数值模拟试验和理论研究的基础上，对热带大气季节内（３０－６０天）振荡的几个基本问题进行系统的综合讨论，包括热带大气季节内振荡的地域特征、空间尺度特征、水平传播特征、与中高纬度大气季节内振荡的联系、同Ｅ１Ｎｉｎｏ间的相互作用以及热带大气季节内振荡的动力学机制。通过讨论和分析，对热带大气季节内振荡得到一个更全面和更系统的认识。