NSFGEO-NERC: Wider Impacts of Subpolar nortH atlantic decadal variaBility on the OceaN and atmospherE (WISHBONE)

本项目由美国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委员会（NERC）通过NSF/GEO-NERC牵头机构协议共同资助。该协议允许美国/英国提交一份联合提案，并由其调查员拥有最大比例预算的机构进行同行评审。在成功地共同确定一项奖励后，每个机构为预算的比例和与本国有关的调查人员提供资金。北大西洋亚极地（SNA）是一个高度变化的区域，它是大西洋在45北纬- 65北纬之间的区域。这里的地表温度和地表盐度在一系列时间尺度上变化，以年代际或更长的时间尺度为主导。这种年代际变率似乎构成了一个更大的气候模式——大西洋多年代际变率的关键组成部分，它与一系列重要的气候影响有关，包括北非和南亚季风的降雨、欧洲和北美的洪水和干旱，以及飓风形成的数量。SNA也是地球上十年时间尺度上最可预测的地方之一，这表明有可能改进对未来区域气候和高影响天气年份的预测。然而，这种可变性的起源以及控制其影响的过程还远未完全了解。有重要的证据表明，从亚极地北大西洋到大气的异常热损失可以在整个北大西洋盆地的海洋和大气中引发一连串的变化。例如，SNA的变化可以改变向南的海洋环流强度，影响北大西洋热量和淡水向北输送，进而影响整个北大西洋盆地并进入北极的上层海洋温度和盐度。北大西洋亚极地表面温度的变化也被认为影响了夏季和冬季的大气环流（即风型）。然而，观测记录非常短，因此在理解因果关系方面存在重大问题，并且在当前气候模式中对许多重要过程的表现程度方面存在相当大的不确定性。该项目（WISHBONE）将利用新的先进气候模拟和预报系统，提高我们对北大西洋亚极地对北大西洋盆地影响的认识。它还将测试一些特定的假设，这些假设与了解北大西洋亚极地的热量损失在驱动整个盆地变化中的特定作用有关，包括地面异常在驱动风型方面的作用。该项目将加强与英国的国际合作，科学成果将引起美国和英国公众的兴趣，因为这两个地区都受到SNA变化的影响。NCAR将通过公开讲座、新闻发布会和大学讲座等方式开展外联活动，传播主要发现。预计这项工作将为正在进行的和未来的年代际预测活动提供信息，例如由NCAR和英国气象局领导的活动。WISHBONE的总体目标是在年代际尺度上表征SNA异常浮力强迫与对更广泛的北大西洋耦合系统的影响之间的联系，并确定控制这些影响的海洋和大气过程。WISHBONE将通过关注具体的联系和潜在的过程来做到这一点。因此，该项目的具体目标是：1)确定和评价SNA变化对大西洋盆地低纬度地区产生影响的海洋途径；2)确定不同时间尺度上SNA变化对北大西洋大气环流的影响，并推断其中的重要过程；3)确定SNA变化对高纬度地区和北极影响的海洋和大气路径；4)评估不同分辨率下数值模拟的机制和时间尺度的鲁棒性及其与观测值的一致性；5)探讨人为强迫如何改变SNA的影响。要处理的关键时间尺度是十年，但在国民核算体系年际到百年变化的背景下。主要假设是SNA上的浮力强迫是大西洋年代际-多年代际耦合变率的主要控制因素，因为它在形成横跨北大西洋盆地的热盐环流（THC）以及随后导致大气响应的上层海洋变化中起关键作用。具体的假设包括：1)SNA的地下密度异常沿西边界向下传播，影响低纬度的AMOC和墨西哥湾流延伸（GSE）；2) SNA海温强迫夏季和冬季大气涡旋驱动急流的速度和/或纬度变化，对急流的年代际变率有贡献；3) SNA的地下密度异常是成功预测SNA主要变化（如90年代中期变暖）和相关AMV相位变化的关键因素。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 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 (SNA), which is the region of the Atlantic Ocean between 45N - 65N latitude, is a highly variable region. Surface temperatures and surface salinity here have varied on a range of timescales with those on decadal or longer being the dominant ones. This decadal timescale variability appears to form a key component of a larger climate mode, the Atlantic Multidecadal Variability, which has been linked to a broad range of important climate impacts, including rainfall in the North African and south Asian monsoons, floods and droughts over Europe and North America, and the number of hurricane formations. The SNA is also one of the most predictable places on Earth at decadal timescales, which suggests there is potential for improved predictions of regional climate and high-impact weather years ahead. However, the origins of this variability, and the processes controlling its impacts, are far from fully understood. There is significant evidence to suggest that anomalous heat loss from the subpolar North Atlantic Ocean to the atmosphere can instigate a cascade of changes across the North Atlantic basin in both the ocean and atmosphere. For example, changes in the SNA can change the strength of the ocean circulation to the south, affect the northward transport of heat and freshwater in the North Atlantic, and subsequently affect the upper ocean temperatures and salinity across the whole North Atlantic basin, and into the Arctic. Changes in the subpolar North Atlantic surface temperature are also thought to affect the atmospheric circulation (i.e., wind patterns) in both summer and winter. However, observational records are very short, and so there are significant problems with understanding causality, and considerable uncertainty about how well many of the important processes are represented in current climate models. This project (WISHBONE) will make use of new advanced climate simulations and forecast systems to improve our understanding of the impact of the subpolar North Atlantic on the wider North Atlantic basin. It will also test specific hypotheses related to understanding the specific role of heat loss over the subpolar North Atlantic in driving changes throughout the basin including the role of surface anomalies in driving wind patterns. The project will enhance international collaboration with the UK and science results would be of interest to the public in the US and the UK, as both regions are impacted by SNA variability. NCAR will engage in outreach activities to communicate key findings through public lectures, press releases, and university lectures amongst others. It is anticipated that this work will inform ongoing and future decadal prediction activities, such as those led by NCAR and the UK Met Office. The overarching objective of WISHBONE is to characterize the linkages between anomalous buoyancy forcing of the SNA and impacts on the wider North Atlantic coupled system on decadal timescales, and to determine the oceanic and atmospheric processes that control these impacts. WISHBONE will do this by focusing on the specific linkages and underlying processes. Hence, the specific objectives of the project are: 1) to determine and evaluate the oceanic pathways through which changes in the SNA impact on lower latitudes in the Atlantic basin; 2) to determine the impact of changes in the SNA on atmospheric circulation over the North Atlantic on a range of timescales, and to deduce the important processes involved; 3) to determine the oceanic and atmospheric pathways through which changes in the SNA impact on higher latitudes and the Arctic; 4) to assess how robust are the mechanisms and timescales in numerical simulations at different resolutions, and their consistency with observations; 5)to explore how the influence of the SNA is modified by anthropogenic forcing. The key time scale to be addressed is decadal, but in the context of interannual-to-centennial changes in the SNA. The primary hypothesis is that buoyancy forcing over the SNA is the primary controller of Atlantic Decadal-to-Multidecadal coupled variability due to its key role in shaping the Thermohaline Circulation (THC) across the North Atlantic basin and, subsequently, upper ocean changes that result in an atmospheric response. Specific hypotheses include: 1) subsurface density anomalies in the SNA propagate down the western boundary and affect the AMOC at lower latitudes and the Gulf Stream Extension (GSE); 2) SNA SSTs force changes in the speed and/or latitude of the atmospheric eddy-driven jet in summer and winter, contributing to decadal jet variability; 3) subsurface density anomalies in the SNA are a key ingredient for successful predictions of major changes in the SNA (e.g. the mid-1990s warming), and associated changes in phase of the AMV.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.