Collaborative Research: Response of the upper tropical Pacific Ocean to greenhouse gas forcing in observations and models

热带太平洋是全球气候异常的一个公认驱动因素，也是进入大气的二氧化碳通量的最大海洋来源。𝐶𝑂它对温室气体（GHGs）上升的反应将强烈影响未来全球气候的手段和极端和碳循环。气候模型模拟了过去几十年来该地区的变暖，这在观测记录中是看不到的。对这一差异没有明确的解释，也没有明确的解释对未来的预测意味着什么。这项工作将是对热带太平洋对温室气体驱动的热力学和动力学强迫的响应的独特的详细分析，重点是与观测到的和重新分析的海洋环流和温度变化进行比较。虽然许多研究都集中在热带大气对温室气体上升的反应上，但对热带海洋的研究却少得多。因此，该项目将在认识辐射强迫气候变化的背景下热带大气-海洋耦合系统的海洋方面取得重要的知识进步。确定热带太平洋地区如何应对温室气体的上升，对于预测全球区域气候变化和影响大气温室气体的气候碳反馈至关重要。这项工作将促进对减缓和适应气候变化具有重要意义的知识。这项工作将支持两名早期职业研究人员（博士后和研究生）和一名女教师在理解气候系统的关键组成部分如何响应人为强迫方面取得根本性进展。首席PI很好地融入了研究北美干旱风险演变的社区，赤道太平洋是其社会影响的关键驱动力。结果将在那里进行交流，以确定温室气体引起的变化下的短期水文气候预测的错误和狭窄的不确定性。自1960年左右以来，随着温室气体的急剧上升，全球变暖，观测结果显示，赤道太平洋冷舌几乎没有变暖，甚至变冷。相比之下，连续耦合模式相互比较项目（CMIP）中的模式模拟了冷舌的变暖。有人认为，这种差异是由于内部性质的巨大差异，而不是对温室气体的反应。然而，各种研究都表明CMIP模型不太可能与观察结果相匹配，尽管它们在不太可能性上存在差异。另一方面，它已被假设，温室气体的上升导致加强的纬向SST梯度，步行者流通和贸易，动力变浅温跃层和增强冷却的上升流。有人认为，由于模拟热带太平洋大气-海洋系统的偏差，模型的反应在很大程度上是相反的。该项目将研究热带太平洋上层的温度、洋流和热结构如何对温室气体上升作出反应。这是一个深入的调查与观察和模型的时期，到目前为止，模型可以评估。这项工作是围绕解决问题的假设组织的：1）什么是热力学和动力学过程中的相对作用，在确定热带太平洋对温室气体上升的反应？2)气候模式中的偏差（过度的冷舌、过度发展的南部辐合带、过于温暖的东部副热带层云和上升流区域）是否导致上升流和俯冲区域中有偏差的SST响应以及有偏差的进入赤道暗流的输送路径？3)模式偏差是否影响热带太平洋海温对温室气体强迫的响应？主要目标是更好地了解自然界海洋在应对温室气体上升方面的积极作用。模型是这项研究的主要工具。为了应对温室气体的上升，这项工作将研究：在亚热带俯冲后，表面增加的热量如何混合并在内部传输;风应力的变化如何影响电流，上升流，热结构和SST;平均风应力如何影响赤道和亚热带之间的内部路径，因此，冷舌中上升流的温度。响应将被分解与海洋模型的实验，使用欧洲中期天气预报中心再分析验证。实验将强加，在各种组合，模拟和观测场，温室气体引起的加热，再分析和CMIP 6平均和异常风应力。热平衡、示踪剂、解释性人工智能方法和因果路径分析将揭示海洋对观测到的和CMIP 6风应力趋势的响应机制，以及这如何取决于平均海洋状态的扰动，以及被动和动力海洋过程在确定热带太平洋SST趋势中的相对作用。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的学术价值和更广泛的影响审查标准。

The tropical Pacific Ocean is a well-established driver of global climate anomalies and the largest oceanic source of 𝐶𝑂2 flux into the atmosphere. Its response to rising greenhouse gases (GHGs) will strongly influence future global climate means and extremes and the carbon cycle. Climate models simulate a warming in this region for the last several decades, which is not seen in the observational record. There is not a clear explanation of this difference or what it means for future projections. This work will be a uniquely detailed analysis of the tropical Pacific Ocean response to GHG-driven thermodynamic and dynamic forcing focusing on comparisons to observed and reanalyzed changes in ocean circulation and temperature. While much research has focused on the tropical atmosphere’s response to rising GHGs there has been much less work on the tropical oceans. This project will therefore by an important intellectual advance in understanding, in the context of radiatively-forced climate change, the ocean side of the coupled tropical atmosphere-ocean system. Determining how the tropical Pacific responds to rising GHGs is critical to projecting changes in regional climates worldwide and climate-carbon feedbacks that influence atmospheric 𝐶𝑂2. The work will advance knowledge important to climate change mitigation and adaptation. The work will support two early-career researchers (postdoctoral and graduate) and a female faculty member to make fundamental advances in understanding how a key component of the climate system responds to anthropogenic forcing. The lead PI is well integrated into the community researching evolving drought risk over North America, for which the equatorial Pacific is a key driver, and its societal impacts. Results will be communicated there to identify errors and narrow uncertainties regarding near-term hydroclimate projections under GHG-induced changeAmidst the global warming accompanying the sharp rise in GHGs since circa 1960 observations show little warming or even cooling in the equatorial Pacific cold tongue. In contrast, models within successive Coupled Model Intercomparison Projects (CMIPs) simulate warming of the cold tongue. It has been argued that this discrepancy is due to strong internal variations in nature rather than a response to GHGs. Yet various studies all show it is unlikely that CMIP models can match the observations, though they differ on just how unlikely. On the other hand, it has been hypothesized that rising GHGs lead to strengthening of the zonal SST gradient, Walker circulation and trades, a dynamically-shoaled thermocline and enhanced cooling by upwelling. Models, it is argued, have a largely opposite response due to biases in simulating the tropical Pacific atmosphere-ocean system. This project will address how the temperature, currents and thermal structure of the upper tropical Pacific Ocean respond to rising GHGs. It is a deep investigation with observations and models of the period to date for which models can be evaluated. The work is organized around hypotheses that address the questions: 1) what are the relative roles of thermodynamic and dynamic processes in determining the tropical Pacific Ocean response to rising GHGs? 2) do biases in climate models (excessive cold tongue, overdeveloped southern convergence zone, too-warm eastern subtropical stratus cloud and upwelling regions) lead to biased SST responses in upwelling and subducting regions and biased transport pathways into the Equatorial Undercurrent? 3) do model biases influence the response of tropical Pacific SSTs to GHG forcing? The main goal is to better understand the active role of nature’s ocean in the response to rising GHGs. Models are primary tools for this investigation. In response to rising GHGs the work will examine: how heat added at the surface is mixed down and transported in the interior after subduction in the subtropics; how changes in wind stress impact currents, upwelling, thermal structure and SST; how mean wind stress influences interior pathways between the equator and the subtropics and, hence, the temperature of water upwelling in the cold tongue. The responses will be decomposed with experiments with ocean models using European Center for Medium Range Weather Forecasts reanalyses for validation. The experiments will impose, in various combinations, modeled and observed fields, GHG-induced heating, and reanalyzed and CMIP6 mean and anomalous wind stresses. Heat budgets, tracers, Explanatory Artificial Intelligence methods and causal pathway analysis will reveal the mechanisms of ocean responses to observed and CMIP6 wind stress trends, how this depends on the mean ocean state being perturbed, and the relative roles of passive and dynamical ocean processes in determining trends in tropical Pacific SSTs.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.