Collaborative Research: Extratropical Triggering of El Nino/Southern Oscillation (ENSO) Events Through the Trade-Wind Charging Mechanism

合作研究：通过信风充电机制触发厄尔尼诺/南方涛动（ENSO）事件的温带事件

• 批准号: 1547137
• 负责人: Benjamin Kirtman
• 金额: $ 34.35万
• 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: 2016
• 资助国家: 美国
• 起止时间: 2016-09-15 至 2021-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1547137&HistoricalAwards=false
• 关键词: Collaborative; Research; Extratropical; Triggering; El

El Nino/Southern Oscillation (ENSO) events affect weather and climate worldwide, with El Nino impacts over the United States including flooding in California, mild winters in Alaska and the northern tier, and drier conditions in the Ohio valley, with largely opposite conditions during La Nina, or cold phase ENSO, events. The predictability of ENSO is a matter of both practical and scientific interest, and there have been many efforts to identify precursor patters in sea surface temperature (SST), sea level pressure (SLP), and other variables so that the onset of ENSO events can be anticipated several months to seasons in advance. The PIs have proposed a novel mechanism through which changes in surface wind over the North Pacific associated with the North Pacific Oscillation (NPO, a prominent mode of Northern Hemisphere climate variability) can lead to ENSO events 9 to 12 months later. The mechanism, dubbed trade-wind charging (TWC), involves the southward transport of relatively warm subsurface waters from the central subtropical North Pacific, driven by the curl of the surface wind stress anomalies associated with the NPO (a Sverdrup transport). The southward heat transport warms the ocean thermocline in the central equatorial Pacific, thus creating favorable conditions for the development of an El Nina event (a similar chain of events can promote a La Nina event starting from the opposite phase of the NPO). The examination of the TWC mechanism involves testing three related hypotheses: 1) Positive and negative trade wind charging (TWC) of the equatorial Pacific heat content in isolation is sufficient to generate warm and cold boreal winter ENSO events, respectively; 2) Positive and negative TWC enhances the efficacy of initial subsurface ocean conditions in generating warm and cold boreal winter ENSO events; and 3) Positive TWC enhances the efficacy of Meridional Mode (MM) dynamics in generating warm boreal winter ENSO events. The research is performed through experiments with a climate model, the Coupled Model version 2.5 developed at the NOAA Geophysical Fluid Dynamics Laboratory. In one set of experiments, the ocean component model is integrated subject to surface atmospheric conditions taken from reanalysis products, so that the ocean state bears the imprint of an observed NPO event, after which the ocean is coupled to the atmospheric component model and the fully coupled climate model is integrated for several additional months to track the development (or lack thereof) of a TWC-induced ENSO event. The work has broader impacts due to the societal value of better long-lead predictions of ENSO events, as noted above. More specifically, the research offers specific targets for the evaluation of operational forecast model used for ENSO prediction, and the PIs plan to develop an index that can be used to monitor TWC behavior relevant to ENSO prediction. In addition, the project supports a graduate student and a postdoctoral research associate, thereby providing future workforce development in this research area.

El Nino/Southern振荡（ENSO）事件会影响全球的天气和气候，埃尔尼诺（El Nino）对美国的影响，包括加利福尼亚州的洪水，阿拉斯加的轻度冬季和北部地区的温和冬季，以及俄亥俄州山谷中的干燥条件，在拉尼娜（La Nina）或冷阶段ENSO，活动期间的情况很大相反。 ENSO的可预测性既是实用和科学兴趣的问题，并且已经做出了许多努力，以确定海面温度（SST），海平面压力（SLP）和其他变量的前体模式，因此可以预期ENSO事件的发作几个月。 PI提出了一种新的机制，通过该机制，与北太平洋振荡相关的北太平洋（NPO，北半球气候变化的突出模式）的表面风变化可能会导致9到12个月后的ENSO事件。该机制被称为贸易风（TWC），涉及从与NPO相关的表面风应力异常（SVERDRUP运输）的表面风应力异常驱动的相对温暖的地下水。向南的热运输温暖了中央赤道太平洋中的海洋热跃层，从而为El Nina事件的发展创造了有利的条件（类似的事件链可以从NPO的相对阶段开始促进La Nina事件）。对TWC机制的检查涉及测试三个相关的假设：1）赤道太平洋热含量的正贸易和负贸易充电（TWC）分别足以产生温暖和冷的寒冷的北方冬季ENSO事件； 2）阳性和负TWC增强了初始地下海洋条件在产生温暖和寒冷的北方冬季ENSO事件中的功效； 3）阳性TWC增强了子午模式（MM）动力学在产生温暖的北方冬季ENSO事件中的功效。这项研究是通过气候模型的实验进行的，这是在NOAA地球物理流体动力学实验室开发的耦合模型2.5。在一组实验中，海洋组件模型由重新分析产品采取的表面大气条件进行整合，因此海洋国家带有观察到的NPO事件的烙印，此后，海洋与大气组件模型耦合，并且完全耦合的气候模型会集成了几个月，以跟踪（或缺乏该事件的EN）。如上所述，由于对ENSO事件的更好长期预测的社会价值，这项工作具有更大的影响。更具体地说，该研究提供了用于评估用于ENSO预测的操作预测模型的特定目标，并且PIS计划开发可用于监视与ENSO预测相关的TWC行为的索引。此外，该项目还支持研究生和博士后研究助理，从而在该研究领域提供未来的劳动力发展。