Revisiting Coupled Instability Theory and the Initiation of ENSO (El Nino/Southern Oscillation)

重新审视耦合不稳定理论和 ENSO（厄尔尼诺/南方涛动）的引发

• 批准号: 1450811
• 负责人: Benjamin Kirtman
• 金额: $ 17.76万
• 依托单位: University of Miami
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-03-01 至 2017-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1450811&HistoricalAwards=false
• 关键词: Revisiting; Coupled; Instability; Theory; Initiation

Warm El Nino/Southern Oscillation (ENSO) events are climatic fluctuations in which sea surface temperature (SST) along the central-eastern equatorial Pacific is relatively warm, accompanied locally by lower sea level pressure (SLP), with higher SLP on the western side of the basin. Cold ENSO events have the same pattern but with the SST and SLP anomalies reversed, so that SST is colder and SLP is higher along the central-eastern equatorial Pacific. Classical theories view ENSO events as the result of an instability of the coupled atmosphere-ocean system, in which the atmospheric circulation anomalies associated with the SLP anomalies reinforce the oceanic anomalies associated with the SST change and vice versa, thereby enabling a weak initial perturbation to grow into a fully-developed ENSO event. Early studies demonstrated that instability theory can account for ENSO-like behavior in highly simplified models of the equatorial Pacific ocean-atmosphere system. More recent research using sophisticated models and observational analysis suggests that various forms of precursors and triggers, some external to the equatorial Pacific, can play a key role in ENSO initiation. But while precursors and triggers can be identified for some ENSO events, other events appear to initiate without them. There are also instances in which conditions appear favorable for an ENSO event but initiation does not occur.This research seeks to determine the essential elements for ENSO initiation through model experiments in which ENSO events are initiated starting from an atmosphere-ocean state which contains virtually no ENSO activity. The ENSO-free initial state is generated through a spin-up procedure in which an atmosphere-ocean general circulation model (GCM) is modified so that the ocean component model does not feel the effect of atmospheric circulation anomalies (more precisely, surface wind stress anomalies) over the equatorial Pacific. Out of 60 simulations performed in preliminary work for the project, 10 developed strong warm ENSO events and 13 developed strong cold events. Work performed under this award analyzes these experiments and conducts additional experiments to determine why some simulations produced warm events while others developed cold events or near-neutral conditions.The work has broader societal impacts due to the variety of ways in which ENSO events affect weather and climate over the US and other parts of the world. A better understanding of the key factors in ENSO initiation may lead to better ENSO predictions, and in particular a reduction in the occurrence of "false alarms" in which an ENSO event is predicted but does not materialize. In addition, the project supports a female graduate student, thereby developing the future workforce in this research area, and enhancing the participation of an underrepresented group.

暖厄尔尼诺/南方涛动（ENSO）事件是赤道太平洋中东部海表温度（SST）相对温暖的气候波动，局部伴有较低的海平面压力（SLP），盆地西侧的SLP较高。冷ENSO事件具有相同的模式，但海温和海面高度异常相反，因此赤道太平洋中东部海温更冷，海面高度更高。经典理论认为ENSO事件是大气-海洋耦合系统不稳定的结果，其中与SLP异常相关的大气环流异常加强了与海温变化相关的海洋异常，反之亦然，从而使一个微弱的初始扰动发展成为一个充分发展的ENSO事件。早期的研究表明，在赤道太平洋-大气系统的高度简化模型中，不稳定性理论可以解释类似enso的行为。最近使用复杂模型和观测分析的研究表明，各种形式的前体和触发因素，有些在赤道太平洋之外，可以在ENSO的启动中发挥关键作用。但是，虽然可以确定某些ENSO事件的前体和触发因素，但其他事件似乎在没有它们的情况下启动。也有些情况下，条件似乎有利于ENSO事件，但没有发生启动。本研究试图通过模式实验确定ENSO启动的基本要素，在模式实验中，ENSO事件是从几乎不包含ENSO活动的大气-海洋状态开始启动的。ENSO-free初始状态是通过一个自旋上升过程产生的，在这个过程中，一个大气-海洋环流模式（GCM）被修改，这样海洋分量模式就不会感受到赤道太平洋上空大气环流异常（更准确地说，地面风应力异常）的影响。在项目前期工作中进行的60次模拟中，有10次发生了强暖ENSO事件，13次发生了强冷事件。在该奖项下进行的工作分析了这些实验，并进行了额外的实验，以确定为什么一些模拟产生了温暖事件，而另一些模拟产生了寒冷事件或接近中性的条件。由于ENSO事件以各种方式影响美国和世界其他地区的天气和气候，这项工作具有更广泛的社会影响。更好地了解ENSO启动的关键因素可能导致更好的ENSO预测，特别是减少“假警报”的发生，即ENSO事件被预测但没有实现。此外，该项目支持一名女研究生，从而发展该研究领域的未来劳动力，并加强代表性不足的群体的参与。