NSFGEO-NERC: Collaborative Research: Subpolar North Atlantic Processes - Dynamics and pRedictability of vAriability in Gyre and OverturNing (SNAP-DRAGON)

这是一个由国家科学基金会地球科学理事会(NSF/GEO)和英国国家环境研究理事会(NERC)通过NSF/GEO-NERC牵头机构协议共同资助的项目。该协定允许美国和英国提交一个单一的联合提案，并由该机构进行同行审查，该机构的调查员在预算中所占比例最大。在成功地联合确定一项裁决后，每个机构将为与其本国有关的预算和调查员的比例提供资金。亚极地北大西洋横跨英国、格陵兰和加拿大，对当地和全球气候起着至关重要的作用。这是一个关键区域，北大西洋上层向北流动的大部分暖水将其热量释放到大气中，并转化为冷水和稠密水，然后再次向南流动，形成所谓的大西洋翻转环流。这种环流向北输送并释放到大气中的大量热量影响了风暴的路径，并决定了西欧的天气。翻转的环流还通过其对较低纬度海洋表面温度的影响，对非洲降雨和飓风发展产生深远影响。此外，亚极区的水下沉使深海通风，将热量和碳从表面转移出去，并缓和了人为温室气体对表面温度的影响。任何不在亚极地地区下沉的温暖水都会再循环或将其热量进一步向北带向北极，在下沉和向南流动之前影响海冰条件和极地海洋生态系统。这项研究旨在使我们对将大气变化与亚极地海洋变率联系起来的过程、它们对该区域海洋和气候可预测性的影响以及我们在气候模型中的表现的信任程度的认识发生阶段性的变化。最近，亚极北大西洋计划(OSNAP，www.o-Snap.org)中的翻转环流首次观测到了亚极北大西洋的翻转环流。这些数据揭示了倾覆过程中的巨大幅度变化，并提出了引起这种变化的地点和过程及其可能对表层海洋状况和气候产生的影响的问题。在气候模型中适当地表示该地区对于在季节、年际、年代际和更长的时间尺度上做出有用的气候预测是至关重要的。然而，当前一代模型很难代表已知在这里很重要的过程，并与关于温水转化为稠水的位置的观察结果不一致。分歧限制了我们对模型预测的信心。科学界无法正确评估模型的性能，因为对大气条件和海洋环流可变性之间的所有联系的了解有限。该项目将把OSNAP和其他观测与能够代表小尺度过程的数值模式结合起来，以揭示亚极地海洋环流变化的原因。一旦明确了哪些过程是最重要的，以及它们是如何工作的，该团队将能够确定哪些气候模型出错并提出改进建议。这将改善对亚极地北大西洋及更远地区海洋和气候变化的预测。该小组将调查冰冷、稠密的海水如何进入边界洋流，然后将它们输出到南方。它将确定风所扮演的角色，这可能比我们过去假设的要复杂得多，它将确定北极和格陵兰淡水出口变化对颠覆变异性的影响。为了表征和量化这些关键过程，除了使用海洋观测，调查人员还将执行“如果呢？”在海洋模型中进行实验，提出这样的问题：如果大西洋上空的大气急流移动或加强，亚极地海洋环流会发生什么？他们将使用天气预报中更常见的统计方法来弄清楚亚极地海洋的性质和倾覆如何与潜在的可预测的更大规模的大气环流模式联系起来。模型与观测相结合的创新方法将被用来确定在OSNAP观测期内北大西洋次极地演变的最佳估计。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This is a project that is jointly funded by the National Science Foundation's Directorate of Geosciences (NSF/GEO) and the National Environment Research Council (NERC) of the United Kingdom (UK) via the NSF/GEO-NERC Lead Agency Agreement. This Agreement allows a single joint US/UK proposal to be submitted and peer-reviewed by the Agency whose investigator has the largest proportion of the budget. Upon successful joint determination of an award, each Agency funds the proportion of the budget and the investigators associated with their own country. The subpolar North Atlantic Ocean, stretching between the UK, Greenland, and Canada, plays a crucial role in local and global climate. This is the critical region where much of the warm water flowing northward in the upper North Atlantic releases its heat to the atmosphere and is converted to cold, dense water, before flowing southward again at depth in what is known as the Atlantic overturning circulation. The large amount of heat this circulation carries northward and releases to the atmosphere impacts the track of storms and determines the weather over western Europe. The overturning circulation also has profound implications for African rainfall and hurricane development via its effect on sea surface temperature at lower latitudes. In addition, the sinking of water in the subpolar region ventilates the deep ocean, transferring heat and carbon away from the surface and moderating the impact of anthropogenic greenhouse gases on surface temperature. Any warm water which does not sink in the subpolar region recirculates or carries its heat further north towards the Arctic, influencing sea-ice conditions and polar marine ecosystems before it too sinks and flows south. This study aims to produce a step change in our understanding of the processes that link atmospheric changes to subpolar ocean variability, their implications for ocean and climate predictability in this region, and the degree to which we can trust their representation in climate models. Recently, the first ever observations of the overturning circulation in the subpolar North Atlantic have been made by the Overturning in the Subpolar North Atlantic Program (OSNAP, www.o-snap.org). These have revealed large amplitude variations in the overturning and raised questions about the locations and processes that give rise to this variability and its likely impact on surface ocean conditions and climate. Representing this region properly in climate models is essential for making useful climate predictions on seasonal, interannual, decadal and longer timescales. However, the current generation of models struggle to represent the processes known to be important here and disagree with the observations on the locations in which warm water is transformed into dense water. The disagreements limit our confidence in model predictions. The scientific community cannot assess model performance properly because there is limited understanding of all the links between atmospheric conditions and ocean circulation variability. This project will combine OSNAP and other observations with numerical models that can represent small-scale processes to reveal the cause of the variations in subpolar ocean circulation. Once it is clear which processes are most important and how they work, the team will be able to establish what climate models are getting wrong and suggest improvements. This will improve predictions of ocean and climate variability in the subpolar North Atlantic and beyond. The team will investigate how cold, dense waters find their way into the boundary currents that export them to the south. It will establish the role that winds play, which is likely more complicated than we have assumed in the past and it will determine the impact on overturning variability of changes in freshwater export from the Arctic and Greenland. To characterize and quantify these key processes, in addition to using ocean observations, the investigators will perform "What if?" experiments in ocean models, asking questions such as: what happens to the subpolar ocean circulation if the atmospheric jet stream over the Atlantic shifts or strengthens? They will use statistical methods more common in weather forecasting to figure out how subpolar ocean properties and overturning connect to potentially predictable larger-scale atmospheric circulation patterns. Innovative ways of combining models with observations will be used to determine a best estimate of the evolution of the subpolar North Atlantic over the OSNAP observation period.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.