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El Nino/Southern Oscillation（ENSO）事件是指赤道太平洋中东部沿着海表温度（SST）相对偏暖，并伴有海平面气压（SLP）局部偏低，且海平面气压偏高的气候波动。 冷ENSO事件具有相同的模式，但SST和SLP异常相反，即赤道中东部太平洋的SST较冷，SLP沿着较高。 经典理论认为ENSO事件是海气耦合系统不稳定的结果，与海平面气压异常相关的大气环流异常加强了与海表温度变化相关的海洋异常，反之亦然，从而使一个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，不稳定性理论可以解释赤道太平洋海洋-大气系统高度简化模式中的ENSO行为。最近利用精密模型和观测分析进行的研究表明，各种形式的前兆和触发因素，有些在赤道太平洋以外，可在厄尔尼诺/南方涛动的启动中发挥关键作用。 但是，虽然可以确定某些厄尔尼诺/南方涛动事件的前兆和触发因素，但其他事件似乎在没有这些前兆和触发因素的情况下就开始了。 也有一些情况下，条件看似有利于ENSO事件，但并未发生引发。本研究旨在通过模式实验确定ENSO事件的基本要素，其中ENSO事件从几乎不包含ENSO活动的大气-海洋状态开始引发。 无ENSO初始状态是通过自旋上升过程产生的，在该过程中，大气-海洋环流模式（GCM）被修改，使海洋成分模式不会感受到赤道太平洋上空大气环流异常（更准确地说，表面风应力异常）的影响。 在项目初步工作中进行的60次模拟中，有10次出现了强暖厄尔尼诺/南方涛动事件，13次出现了强冷厄尔尼诺/南方涛动事件。 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温暖的事件，而其他人开发冷事件或近中性条件。由于ENSO事件影响美国和世界其他地区天气和气候的各种方式，这项工作具有更广泛的社会影响。 更好地了解厄尔尼诺/南方涛动发生的关键因素可能会导致更好的厄尔尼诺/南方涛动预测，特别是减少“假警报”的发生，即预测到厄尔尼诺/南方涛动事件但没有发生。 此外，该项目还支持一名女研究生，从而培养这一研究领域的未来劳动力，并提高代表性不足群体的参与程度。