Recent Changes of Sea Level and Circulation around the Grand Banks: Local Dynamics and Broader Connections

该项目将使用观测分析、数据模型结果（再分析产品）、现实和理想化模型模拟以及简化的两层过程模型，检查美国东北海岸和墨西哥湾流之间的卫星测高中看到的大异常海面高度（SSH）。例如，2008-2018年，大浅滩上空的海面高度比1993-2007年高出约7-8厘米。但其原因和对区域水运动的潜在影响，包括拉布拉多海流、陆架和斜坡海流的连续性，仍是未知的。海平面变化对海岸生境、海岸灾害和湿地生态系统有着广泛的影响。已确定的海平面异常伴随着大陆架上水温的迅速上升，这已知对渔业和水产养殖业产生不利影响。该项目将：1)研究陆架斜坡区这一巨大海平面异常的强迫机制；2)研究大陆架上的海平面变化与公海上的海平面变化是如何联系在一起的；3)调查纽芬兰和苏格兰大陆架的海平面变化是否以及如何影响美国东北部的沿海环流和海平面。项目pi将向NOAA东北渔业科学中心、商业渔业研究基金会和更广泛的渔业社区通报相关结果，并参与一系列外联和教育活动，包括努力吸引代表性不足的少数民族。拟议的工作与美国CLIVAR科学计划附录“海岸气候研究挑战”相一致，预计将引起科学界和公众的广泛兴趣。该项目确定了七个假设，涵盖了上述三个感兴趣的领域。第一，在强迫机制方面：与AMOC减弱或副热带和亚极地盆地风环流变化有关的西部边界流的H1A变化是观测到的海平面异常的原因；H1B—地表风应力旋度的变化导致海面高度异常；H1C -暖核环数量的增加有助于质量和空间热通量，与WCR活动增加相关的空间热通量有助于观测到的海平面变化。第二，关于跨大陆架连接的SSH变异性：H2A—底部Ekman层的跨大陆架运输在跨大陆架连接中起重要作用；H2B—地面风致Ekman层也起重要作用；H2C -涡旋PV通量增加，增强了SSH异常的跨大陆架连通性。第三，关于大浅滩和哈特拉斯角之间的连接：H3A -纽芬兰和苏格兰大陆架上的海平面异常对沿大陆架流动产生了相当大的影响，可能增强了从纽芬兰到哈特拉斯角的赤道流动。建模和数据分析都将用于解决这些假设。使用的数据范围相当广泛，包括：网格化的海面高度测量、全球海洋和大气再分析、基于观测的热通量、蒸发和风应力，以及OOI先锋阵列和夹叶树线的当地多年原位数据。建模将利用一种新的西北大西洋区域环流模式，该模式包括拉布拉多海和大西洋中部的整个大陆架和斜坡区，具有亚中尺度，允许水平分辨率为2公里，垂直层数为40层。两层模型将与实际的区域环流模型并行用于过程建模，以帮助指导数据分析和NWA模型模拟的分析和解释，从而帮助隔离关键过程和机制。该模型采用了真实的测深和强迫，并分解了正压和第一次斜压模态。这项研究将使人们更好地了解动态过程如何在快速变化的气候系统中相互作用，沿海海洋如何响应开放海洋中气候引起的变化，并为美国东北部大陆架环流的可预测性提供信息。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 project will examine large anomalous sea surface height (SSH) seen in satellite altimetry between the U.S. northeast coast and the Gulf Stream, using analyses of observations, data-model results (reanalysis products), realistic and idealized model simulations, and a simplified 2-layer process model. For example, the sea-surface height seen over the Grand Banks was about 7-8 cm higher in 2008-2018 than in 1993-2007. But still unknown are its causes and potential effects on the regional water motions, including the continuity of the Labrador Current and shelf and slope currents. Sea-level changes have broad impacts on coastal habitats, coastal hazards, and wetland ecological systems. The identified sea-level anomaly is accompanied by a rapid rising of water temperature on the shelves, which is known to have adverse impacts on the fishing industry and aquaculture. The project would: 1) investigate forcing mechanisms of this large sea level anomaly in the shelf-slope region; 2) examine how sea-level change on the continental shelf is connected to that in the open ocean; and 3) investigate whether and how the sea level changes on the Newfoundland and Scotian shelves may have affected coastal circulations and sea level off the Northeast US. Project PIs will keep NOAA Northeast Fishery Sciences Center, the Commercial Fisheries Research Foundation, and the wider fishing industry communities informed of relevant results, and engage in a range of outreach and educational activities, including efforts to engage underrepresented minorities. The proposed work is aligned with US CLIVAR Science Plan Addendum "Research Challenge on Climate at the Coasts," and is expected to generate broad interest from both the scientific community and the general public. The project identifies seven hypotheses covering the three areas of interest identified above. For the first, concerning forcing mechanisms: H1A - changes in western boundary currents related to a weakening AMOC or changing wind-driven gyres in subtropical and subpolar basins contribute to the observed SSH anomaly; H1B - a change in surface wind-stress curl forces the observed SSH anomaly; H1C – an increase in the number of warm core rings contribute to both mass and steric heat fluxes associated with increased WCR activity contribute to the observed SSH changes. For the second, concerning the cross-shelf connection of SSH variability: H2A - the cross-shelf transport in the bottom Ekman layer plays an important role in the cross-shelf SSH connectivity; H2B - the surface wind-driven Ekman layer plays an important role as well; H2C - eddy PV flux increased and contributed to enhanced cross-shelf connectivity in SSH anomaly. For the third, concerning connections between Grand Banks and Cape Hatteras: H3A - the SSH anomaly on the Newfoundland and Scotian shelves have impacted the along-shelf flows considerably, likely enhancing the equatorward flow from Newfoundland to Cape Hatteras. Both modeling and data analysis will be used to address these hypotheses. The fairly wide range of data used will include: gridded SSH altimetry, global ocean and atmosphere reanalyses, observation-based heat fluxes, evaporation and wind stress, and local multi-year in-situ data from the OOI Pioneer Array and the Oleander line. Modeling will utilize a new Northwest Atlantic Regional Circulation Model, which encompasses the entire shelf and slope region of the Labrador Sea and the Middle Atlantic Bight with a submesoscale-permitting horizontal resolution of 2-km and 40 vertical layers. A two-layer model will be used in parallel with the realistic regional circulation models for process modelling, to help guide analyses and interpretations of data analyses and NWA model simulations, as to help isolate key processes and mechanisms. This model uses realistic bathymetry and forcing and resolves the barotropic and the 1st baroclinic modes. The study will lead to a better understanding of how dynamical processes interact in a rapidly changing climate system, how coastal oceans respond to climate-induced changes in the open ocean, and inform predictability of the Northeast US shelf circulation.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.