1993年El Nino夭折事件及其与典型El Nino事件的对比分析

除正常的El Nio事件外,赤道中东太平洋存在一些类似但又显著不同的海水增暖事件。以1993年为例,海水增暖事件发生在3月,5月最强,但随后迅速衰减,在此称之为El Nio的夭折。通过与典型El Nio事件的对比分析,研究了1993年暖水事件的演变特征及其夭折原因。研究发现,1993年暖水事件是一种发生在热带中东太平洋的局地海气作用现象。由于1991～1992年发生了一次较强的El Nio事件,造成1992～1993年热带西太平洋暖池持续偏冷,使得1993年缺乏发生正常El Nio事件所需要的热力条件。在此背景下,虽然在春季出现赤道西风异常自西太平洋向东太平洋扩展,满足了El Nio事件发生的动力条件,但由于暖池偏冷,不能引发海盆尺度的Bjerknes型正反馈,使得赤道中东太平洋的海水增暖只是一种短期现象,并迅速衰减,造成ElNio事件的夭折。

The Abortion of the El Nino Event in 1993 and Its Comparison with the Typical El Nino Event

Over the equatorial central-eastern Pacific,there is an anomalous seawater warming event that is significantly different from the typical El Nio event.In 1993,for example,an anomalous warming event occurred in March with its peak in May,then it decayed rapidly.This warming event is referred to abortion of an El Nio event.By comparing the event in 1993 with the typical El Nio event,the authors explore the feature and the cause of the abortion of this event.It is found that the event in 1993 is a local air-sea coupling phenomenon in the tropical central-eastern Pacific.Due to the relatively strong El Nio event during 1991-1992,the western Pacific warm pool was anomalously cold during 1992-1993,and the thermal condition was not suitable for the occurrence of an El Nio event in 1993.In this case,the eastward extension of the equatorial westerly anomaly in spring from the western Pacific to the central Pacific satisfied the dynamical condition for the occurrence of an El Nio event,but the basin-scale Bjerknes-type positive feedback failed to work due to the cold warm pool.As a result,the seawater warming in the equatorial central-eastern Pacific lasted for a short period,then it decayed rapidly,causing the abortion of an El Nio event.