Fourth CLIVAR Workshop on the Evaluation of ENSO Processes in Climate Models: ENSO in a Changing Climate
Fourth CLIVAR Workshop on the Evaluation of ENSO Processes in Climate Models: ENSO in a Changing Climate
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第四届 CLIVAR 气候模型中 ENSO 过程评估研讨会：气候变化中的 ENSO
DOI：
10.1175/bams-d-15-00287.1
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发表时间：
2016
影响因子：
8
通讯作者：
Guilyardi E
中科院分区：
文献类型：
--
作者：
Guilyardi E
817 2016 年 5 月 美国气象学会 |以及历史和古观察。讨论会的重点是模型评估和指标，以及对未来观测的设想，作为热带太平洋观测系统 2020 (TPOS 2020) 计划的一部分。研讨会明确指出，观测到了大量与 ENSO 相关的大气和海洋现象。一些演讲强调了风变率和赤道太平洋云的重要性及其随海面温度（SST）的季节性调节反馈。例如，海温与风的关系表现出明显的非线性，赤道中太平洋信风对强厄尔尼诺现象的敏感性高于对拉尼娜现象或中度厄尔尼诺现象的敏感性。热带不稳定波对赤道太平洋冷舌的季节性和 ENSO 调节的平流变暖效应也得到了强调。传统上，赤道初始热含量被视为 ENSO 事件的重要前兆。然而，一个演示表明，耦合模型模拟可以在没有地下前兆或大规模风触发的情况下自发产生 ENSO 事件，尽管幅度减小。另一方面，西风事件与初始地下条件之间的相互作用，无论是补给状态还是中性状态，似乎都通过影响事件沿赤道的位置来促进 ENSO 多样性。一些演讲还讨论了季节内大气变化（西风和东风事件以及马登-朱利安振荡），强调了其对 ENSO 可预测性的重要性。特别是，西风事件的时间顺序被证明会影响其随后的影响。例如，一项模型研究表明，如果 2014 年厄尔尼诺现象只是受到 1997 年 4 月和 6 月发生的（很大程度上随机的）西风事件序列的影响，而不是受到 2014 年 6 月实际发生的强烈东风爆发的影响，2014 年厄尔尼诺现象就会发展成为像 1997 年那样的非常强烈的事件。另一项模型研究强调了离赤道风事件对于补充赤道海洋热含量的重要性，可能 2015 年厄尔尼诺现象紧随 2014 年非事件（也被一些人称为“拉纳达”）之后发展。另一项研究表明，2001 年至 2014 年间模型预报技能大幅下降，这并不是由于预报系统质量下降，而是由于该时期缺乏任何强 ENSO 事件导致信噪比较弱。这种弱ENSO时期在过去曾发生过，也可能随机出现在ENSO物理和统计模型的非受迫模拟中，对可预测性具有类似的影响。尽管ENSO随全球变暖的变化仍然存在很大的不确定性，但大多数未来模型预测表明，未来与ENSO相关的降雨异常强度将会增加。这是赤道信风和冷舌预计减弱的结果，为
817 MAY 2016 AMERICAN METEOROLOGICAL SOCIETY| and historical and paleo-observations. Discussion sessions focused on model evaluation and metrics and on envisioning future observations as part of the Tropical Pacific Observing System 2020 (TPOS 2020) initiative. The workshop made clear that there is a rich set of observed atmospheric and oceanic phenomena associated with ENSO. The importance of wind variability and of equatorial Pacific clouds and their seasonally modulated feedbacks with sea surface temperatures (SSTs) were highlighted in several presentations. For example, the SST–wind relationship exhibits marked nonlinearities, with the central equatorial Pacific trade winds having a greater sensitivity to strong El Niños than to either La Niñas or moderate El Niños. The seasonally and ENSO-modulated advective warming effects of tropical instability waves on the equatorial Pacific cold tongue were also highlighted. The initial equatorial heat content has traditionally been viewed as an essential precursor for ENSO events. However, a presentation showed that coupled model simulations could spontaneously generate ENSO events without subsurface precursors or largescale wind triggers, albeit with reduced amplitude.On the other hand, the interplay between westerly wind events and the initial subsurface conditions, whether recharged or in a neutral state, appears to contribute to ENSO diversity by influencing the location of the event along the equator. Intraseasonal atmospheric variability (both westerly and easterly wind events and the Madden–Julian oscillation) was also addressed in several presentations, highlighting its importance for ENSO predictability. In particular, the temporal sequence of westerly wind events was shown to influence their subsequent impact. For example, a model study indicated that the stunted 2014 El Niño would have developed into a very strong event like that in 1997 had it simply been subjected to the (largely random) sequence of westerly wind events that occurred in April and June of 1997, instead of receiving the strong easterly wind burst that actually occurred in June 2014. Another model study highlighted the importance of off-equatorial wind events for recharging equatorial oceanic heat content, which may have helped to support the development of the 2015 El Niño so close on the heels of the 2014 nonevent (also termed “La Nada” by some). Another study indicated a substantial drop in model forecast skill between 2001 and 2014, not due to any degradation in the quality of the forecast system, but rather due to a weaker signal-tonoise ratio associated with a lack of any strong ENSO events during that time. Such weak-ENSO epochs have occurred in the past and can also appear at random in unforced simulations from both physical and statistical models of ENSO, with similar impacts on predictability. Although there is still a large uncertainty about ENSO changes with global warming, most future model projections suggest a future increase in the intensity of the rainfall anomalies associated with ENSO. This results from a projected weakening of the equatorial trade winds and cold tongue, creating a favorable background for