1997／1998年El Nino事件发生、发展可能机制的进一步研究

基于美国哥伦比亚大学Lamont—Doherty地球观象台LDEO（Lamont—DohertyEarth Observatory）海表温度资料和NCEP／NCAR再分析风场资料，分析了1997／1998年El Nino3期间西太平洋暖池海表温度和西风距平的时间演变特征，同时也分析了东太平洋暖池海表温度和北风距平的时间演变特征。结果表明，1997／1998年El Nino3事件期间，西太平洋暖池海表温度变化及异常西风和东太平洋暖池海表温度变化及异常北风都与Nino3指数变化密切相关。将东、西太平洋暖池及异常北风、西风一并结合起来考虑，进一步研究了1997／1998年El Nino3事件发生、发展的可能机制：异常西风驱动西太平洋暖池东端暖水向东伸展直接有利于赤道东太平洋海表温度增加；异常西风激发东传的暖Kelvin波对东太平洋的冷上升流有抑制作用，从而有利于赤道东太平洋海表温度增加；东传的异常西风可以通过埃克曼漂流效应将赤道两侧的海表暖水向赤道辐合从而加强了赤道附近的下沉流，也有利于赤道东太平洋赤道附近海表温度增加。几乎与此同时，北风距平通过产生北风吹流将东太平洋暖池暖水由北向南输送至赤道附近直接导致Nino3区海表温度增加。上述增温因素的叠加作用共同导致了1997／1998年El Nino事件迅速发生、异常强大。

Further Study on Possible Mechanism for Genesis and Development of 1997/1998 El Nino Event

Based on the Lamont-Doherty Earth Observatory (LDEO) sea surface temperature (SST) and the NCEP/NCAR reanalysis wind, the evolutional features of SST over the eastern Pacific warm pool(EPWP) and north wind anomaly as well as SST over the western Pacific warm pool(WPWP) and west wind anomaly during the 1997/1998 El Nino event are analyzed. The results show that the WPWP SST variation and abnormal west wind, and the EPWP SST variation and abnormal north wind re associated closely with the Nino3 index change during the 1997/1998 El Nino. On the basis of the EPWP and WPWP SST in conjunction with the abnormal north and west wind, the possible mechanism for genesis and development of the 1997/1998 El Nino is studied further. To be specific,abnormal west wind can make the warm water of the east edge of the WPWP extend eastward, which is conductive di-rectly to equatorial eastern Pacific SST increase;the warm Kelvin wave propagating eastward excited bythe abnormal west wind can suppress the cold upwelling flow in the equatorial eastern Pacific, which,in turn, is favorable to equatorial eastern Pacific SST increase;the abnormal west wind propagating east-ward can also make the sea surface warm water near two equatorial laterals converge to the equator by Ekman drifting, which,in turn, strengthens the downwelling flow near the equator, then leading to equa-torial eastern Pacific SST increase. Almost at the same time, the north wind anomaly brings the EPWP warm water to the equatorial vicinity by producing north oceanic flow, which causes directly Ni(n)o3 SST increase. As a result, such factors favoring to SST increase give rise to the quick occurrence and abnor-mal strength of the 1997/1998 El Ni(n)o.