NSFGEO-NERC: Collaborative Research: Assessing the influence of sub-annual variability in the AMOC on the Gulf Stream and the atmosphere

本研究是建立在大西洋经向翻转环流（AMOC）控制北方半球天气和气候的假设之上的。因果关系被设想为通过墨西哥湾流（GS）附近强烈的海气热交换及其对大气极端事件的影响。GS在调节北方天气和气候方面的作用最近得到了相当多的支持。人们感兴趣的部分原因在于，与大气层相比，全球变暖的变异性相对持久，这有可能增加极端天气事件的可预测性。观测结果表明，GS蜿蜒每月的时间尺度显着的变化。在相同的月时间尺度上，实验观察到AMOC的高度可变性。这提供了AMOC和中纬度天气之间通过GS的潜在联系。然而，模型研究尚未就AMOC和GS之间的关系达成一致。造成这些差异的原因有很多，但最重要的解释似乎涉及（缺乏）涡流尺度分辨率（小于0.1度）。在之前的NSF资助下，这个研究小组已经生成了一个涡解北大西洋模拟的集合，这些模拟似乎非常适合解决这些问题。事实上，这是目前美国唯一的涡分辨集合北大西洋模式模拟套件。这些模式的结果将被用来系统地评估AMOC和GS变率之间的关系，明确解决海洋涡旋的影响。这项研究将导致更好地了解AMOC，GS和大气之间的关系，在次年度到年际的时间尺度。具体而言，它将澄清它们相互作用的机制，并确定AMOC和大气之间是否存在每月时间尺度的稳健关系。与以前的非涡流解决研究的比较将有助于评估如何以及当前一代的模型重现这些机制，而海洋对大气的影响的更好的理解可能会提供一个来源的未开发的可预测性。 AMOC在调节全球气候方面发挥着关键作用，并被广泛预测将在世纪发生重大变化。因此，更全面地了解AMOC变化如何影响有影响力的气流，如GS，并在大气中留下印记，将改善变暖情景下气候变化的短期预测和长期预测。将结果与以前的研究进行比较，将有助于区域和气候模型的发展，确定需要什么来适当地捕捉相关的过程。该项目通过培训两名研究生和一名博士后研究员，对海洋和大气以及一般气候动力学进行建模和分析，支持STEM教育。PI有一个强有力的承诺，指导本科生的研究记录，并有一个记录，介绍研讨会和会议与本科生在较小的大学，是不太注重研究，带来更广泛的教育经验，这些学生的推理导致从原因（AMOC）到效果（天气/气候控制）由三个组成部分，这反过来又是这个建议的焦点。(1)极端大气事件通过对风暴路径的巨大但罕见的贡献来控制平均大气场。(2)这些极端的大气事件是由与墨西哥湾流（GS）的热交换，是敏感的GS是在蜿蜒或非蜿蜒状态。(3)GS的（非）蜿蜒状态响应于AMOC变异性。这项研究的重点将主要放在那些已被证明对当地和全球大气产生重大影响的墨西哥湾流属性上。此外，额外的模拟工作将评估AMOC的变化如何通过其对GS变异性的影响而对大气产生影响。这将通过在高分辨率的大气模型模拟中规定GS条件来实现，以系统地评估大气变率和地表热通量对底层海洋的依赖性。最后，将进行耦合高分辨率运行，以阐明大气反馈对海洋的贡献。该奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

This study is built on the hypothesis that the Atlantic Meridional Overturning Circulation (AMOC) is a control on weather and climate in the Northern Hemisphere. The causal link is envisioned to be through the strong air-sea heat exchange near the Gulf Stream (GS) and influence of that on the atmospheric extreme events. The role of the GS in modulating the weather and climate of the Northern Hemisphere has received considerable recent support. Interest in part lies in the relative persistence of GS variability compared to the atmosphere, which offers the potential for increased predictability of extreme weather events. Observations show significant variability in GS meandering on monthly timescales. A high degree of variability in the AMOC has been observed experimentally on the same monthly time scales. This provides a potential connection between the AMOC and mid-latitude weather via the GS. Modelling studies, however, have yet to agree on the relationship between the AMOC and the GS. There are many causes for these discrepancies, but an overarching explanation appears to involve (the lack of) eddy-scale resolution (less than 0.1 degree). Under prior NSF funding, this team of investigators have generated an ensemble of eddy resolving North Atlantic simulations that appear to be ideally suited to address these issues. In fact, this is currently the only eddy-resolving ensemble suite of North Atlantic model simulations in the United States. These model results will be used to systematically evaluate the relationship between the AMOC and GS variability with the influence of ocean eddies explicitly resolved. This research will lead to a better understanding of the relationship between the AMOC, the GS, and the atmosphere, on sub-annual to interannual time scales. Specifically, it will provide clarification on the mechanisms by which they interact and determine whether a robust relationship exists between the AMOC and the atmosphere on monthly timescales. Comparison with previous non-eddy resolving studies will aid in evaluating how well the current generation of models reproduce these mechanisms, whilst an improved understanding of ocean influence on the atmosphere may provide a source of untapped predictability. The AMOC has a critical role in modulating the global climate and is widely projected to change significantly in the 21st century. As such, a more complete understanding of how AMOC variability influences influential currents such as the GS, and imprints onto the atmosphere will improve both near-term forecasts and long-term projections of climate variability under warming scenarios. Comparison of results with previous studies will contribute to regional and climate model development through identifying what is required to properly capture the relevant processes. This project supports STEM education through training of two graduate students and a postdoctoral researcher in the modelling and analysis of both the ocean and the atmosphere, as well as general climate dynamics. The PIs have a strong record of commitment to mentoring undergraduates in research, and have a record of presenting seminars and meeting with undergraduate students at smaller universities that are less research-focused, to bring a broader educational experience to those studentsThe reasoning leading from the cause (AMOC) to effect (weather/climate control) consists of three components which, in turn, are the foci of this proposal. (1) Extreme atmospheric events control mean atmospheric fields through anomalously large, but rare, contributions to the storm track. (2) These extreme atmospheric events are governed by heat exchange with the Gulf Stream (GS), and are sensitive to whether the GS is in a meandering or non-meandering state. (3) The (non)-meandering state of the GS responds to AMOC variability. The focus of the study will primarily be on those Gulf Stream attributes that have been shown to significantly influence the atmosphere locally and globally. Furthermore, additional modelling work will assess how changes in the AMOC, through its influence on GS variability, imprint on the atmosphere. This will be achieved by prescribing GS conditions in high-resolution atmosphere-only model simulations to systematically assess the dependence of atmospheric variability and surface heat fluxes on the underlying ocean. Lastly, coupled high-resolution runs will be conducted to elucidate the contribution of atmospheric feedbacks on the ocean.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.