超强厄尔尼诺事件海洋学特征分析与预测回顾

2015/2016年厄尔尼诺事件被认为是一次与1982/1983和1997/1998年相当的超强事件。基于多套再分析数据，比较了此次事件的海洋上层变量主要特征与历史上两次超强事件的异同，并利用热带太平洋混合层热收支方程对主要物理过程进行了定量分析。研究认为，2015/2016年事件前期为异常高海温东传特征，且前期形成了一次弱的中太平洋型暖事件；但后期表现为弱西传特征，在成熟位相转换成东太平洋型强厄尔尼诺。此次事件中伴随着多次西风爆发事件和开尔文波东传，但赤道开尔文波在盛期基本维持在中东太平洋而不继续东传，赤道外罗斯贝波西传特征亦不明显。相比之下，此次事件在发展-成熟期前后的赤道“热容量放电”过程更加明显些。此次事件异常暖中心位置偏西，其主要原因很可能与赤道东太平洋的强东风异常和冷海水上翻，以及纬向洋流异常和次表层温度异常分布偏西有关；东边界冷水入侵，削弱赤道东太平洋海温异常程度，可能是此次事件位置偏西的直接原因。在海洋上层热量收支中，此次事件中温跃层反馈是促进海温升高和位相转换的最关键过程，纬向平流反馈项亦发挥了重要作用，两种过程共同形成了超强的升温幅度和偏西的异常暖海温分布型。中国国家气候中心新一代ENSO预测系统（SEMAP2.0）每年两次的实际会商预测中给出了较为合理的预测，特别是考虑前期海洋变化预报因子信息的统计模型更好地预测出了海温异常的波动演变状况，成为多方法集合（MME）的重要成员。 

Upper-ocean dynamical features and prediction of the super El Nio in 2015/2016: A comparison with 1982/1983 and 1997/1998

The 2015/2016 El Niño event has been widely accepted as a super event that is comparable to the two events of 1982/1983 and 1997/1998. In the present study, some main features of upper ocean variables during this new super event were compared with those during the two historical super events, and the associated major physical processes were quantitatively diagnosed based on the tropical-Pacific mixed-layer heat budget equation. Results show that during the early stage of this new event, there existed an eastward propagation of Sea Surface Temperature (SST) anomalies and a weak warm-pool El Niño event. However, this super event was featured by a weak westward propagation during its mature phase, when the SST anomaly center shifted westward due to strong easterly wind and cold upwelling anomalies as well as the westward-propagating anomalies of zonal current and subsurface ocean temperature. Cold water invasion in the eastern boundary of the equatorial eastern Pacific weakened SST anomalies there, which was the direct reason for the westward shift of this event. Heat budget analysis suggested that the thermocline feedback was the most important process that induced the SST anomaly increase and phase transition of this new super event, while the zonal advection feedback also played an important role in the formation of the strong warming and westward shift of SST anomalies. During this event, several westerly wind burst (WWB) events occurred and the oceanic Kelvin waves propagated eastward before they basically maintained over the eastern Pacific during the mature period, while there were no evident westward propagation of oceanic Rossby waves over the off-equatorial region. There was an obvious discharging process of the equatorial heat during the developing and mature phases. In addition, the new generation El Niño-Southern Oscillation prediction system (SEMAP2.0) developed in National Climate Center of China yielded reasonable forecasts, which were presented in the two real-time operational discussion meetings during 2014-2016. In particular, the statistical prediction model that considered the preceding variation information of oceanic factors provided better forecasts for the fluctuation and evolution of SST anomaly, and became an important member of multi-method ensemble.