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

本研究建立在大西洋经向翻转环流（AMOC）控制北半球天气和气候的假设之上。预计其因果关系是通过墨西哥湾流附近强烈的海气热交换及其对大气极端事件的影响。GS在调节北半球天气和气候方面的作用最近得到了相当多的支持。部分兴趣在于与大气相比，GS变率的相对持久性，这为增加极端天气事件的可预测性提供了潜力。观测结果显示，在月时间尺度上，GS蜿蜒有显著的变异性。在相同的月时间尺度上，实验观察到AMOC的高度变化。这提供了AMOC和中纬度天气之间通过GS的潜在联系。然而，模拟研究尚未就AMOC和GS之间的关系达成一致。造成这些差异的原因有很多，但一个最重要的解释似乎与（缺乏）涡流尺度分辨率（小于0.1度）有关。在美国国家科学基金会之前的资助下，这个研究小组已经生成了一个解决北大西洋涡旋的模拟集合，似乎非常适合解决这些问题。事实上，这是目前在美国唯一的解决涡旋的北大西洋模式模拟集合套件。这些模式结果将用于系统地评估AMOC和GS变率之间的关系，并明确解决海洋涡旋的影响。这项研究将有助于更好地理解AMOC、GS和大气在亚年际尺度上的关系。具体来说，它将澄清它们相互作用的机制，并确定AMOC和大气之间是否在月时间尺度上存在牢固的关系。与以前的非涡旋解析研究进行比较，将有助于评估当前这一代模式对这些机制的再现程度，同时，对海洋对大气影响的进一步了解可能提供一个尚未开发的可预测性来源。AMOC在调节全球气候方面发挥着关键作用，并被广泛预测在21世纪将发生显著变化。因此，更全面地了解AMOC变率如何影响有影响力的海流，如GS，以及大气上的印记，将改善变暖情景下气候变率的近期预报和长期预估。将结果与以前的研究进行比较，将有助于确定正确捕捉相关过程所需的条件，从而促进区域和气候模式的发展。该项目通过培训两名研究生和一名博士后，在海洋和大气的建模和分析以及一般气候动力学方面支持STEM教育。pi在指导本科生进行研究方面有着良好的记录，并且有在研究较少的小型大学举办研讨会和与本科生会面的记录，为这些学生带来更广泛的教育经验。从原因（AMOC）到结果（天气/气候控制）的推理由三个部分组成，而这三个部分又是本提案的重点。(1)极端大气事件通过异常大但罕见的对风暴路径的贡献来控制平均大气场。(2)这些极端大气事件受与墨西哥湾流（GS）的热交换控制，对墨西哥湾流是否处于蜿蜒或非蜿蜒状态敏感。(3)地表（非）蜿蜒状态响应AMOC的变异。研究的重点将主要放在墨西哥湾流的特性上，这些特性已被证明对当地和全球的大气有重大影响。此外，额外的模拟工作将评估AMOC的变化如何通过其对GS变率的影响对大气产生影响。这将通过在高分辨率大气模式模拟中规定GS条件来实现，以便系统地评估大气变率和地表热通量对海底海洋的依赖。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。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.