2015/2016年超强厄尔尼诺事件基本特征及生成和消亡机制

全球变暖背景下, 2015/2016年超强厄尔尼诺(El Ni?o)事件倍受关注, 此次事件是中部型和东部型El Ni?o的混合。研究发现, 西风爆发和北太平洋经向模态对触发此次事件均有所贡献。通过对比2015/2016年、1997/1998年与中部型事件可知, 2015/2016年事件在暖背景中产生, 其发展形态与中部型事件较为相似, 后期海表面温度异常迅速衰退主要与赤道东太平洋海域持续的东风异常以及纬向平流较弱有关。较之1997/1998年事件, 2015/2016年事件的海洋动力调整较弱, 表现为较弱的温跃层反馈和海洋波动, 纬向平流反馈的贡献大于温跃层反馈, 大气强迫影响显著, 中部海域相关要素异常值较大。在2015/2016年事件期间, 赤道海域以及近赤道海域海洋上层热含量的变化基本呈负相关, 且变化较为同步; 衰退阶段热含量的流失主要集中在5°S—5°N海域, 向两极的热输送明显。

Features of 2015/2016 extreme El Niño event and its evolution mechanisms

In the context of global warming, the 2015/2016 extreme El Ni?o event received much attention. This event was a mixture of central Pacific (CP) and eastern Pacific El Ni?o. Our study shows that both the westerly wind bursts and the North Pacific Meridional Mode contributed to the generation of this event. By comparing the 1997/1998 event, the 2015/2016 event and the CP event, the 2015/2016 event occurred in the warm background and shared similar development pattern with the CP event. What’s more, the rapid decline of sea surface temperature anomaly in the 2015/2016 event was related to the continued easterly anomalies and the weakened zonal current advection in the eastern equatorial Pacific. Compared with the 1997/1998 event, the ocean dynamic adjustment of the 2015/2016 event was weak, which was mainly reflected by weaker thermocline feedback and its associated fluctuations near the equator. Moreover, the zonal advection feedback was more efficient than the thermocline feedback, and the atmospheric forcing and its anomalous values in the central equatorial Pacific were larger. In addition, during the 2015/2016 event, the changes of the upper-ocean heat content in the equatorial region and the near- equatorial region were basically negatively correlated, and the changes were relatively synchronous. In the decay phase, the loss of ocean heat content mainly occurred in the 5°S-5°N region with significant heat transport to the higher latitudes.