Fresh water content and circulation variability in the North Atlantic: Are they related?

北大西洋的淡水含量和环流变化：它们是否相关？

• 批准号: 0751896
• 负责人: Ruth Curry
• 金额: $ 43.4万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-03-15 至 2012-02-29
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0751896&HistoricalAwards=false
• 关键词: Fresh; water; content; circulation; variability

The observational record exhibits clear evidence of large amplitude, decadal to multi-decadal variability in sub-polar fresh water (FW) storage and gyre strength, but is barely long enough to have measured a single 50-year cycle. The Atlantic Meridional Overturning Circulation (AMOC) has been directly measured for even less time, and certainly not long enough to identify correlative behavior. A substantial number of observational and model studies have focused on various aspects of this topic, but have not yet produced a unified picture of how this part of the ocean system operates. The disparate range of interpretations for the causes and consequences of observed and modeled North Atlantic FW content and circulation variability has motivated an attempt to better sort them out. A model?data intercomparison study is proposed which will investigate the timing, amplitude and variability of FW content in relation to the full three-dimensional (gyre and overturning) circulation variability and property fluxes in the North Atlantic. A suite of analytical indices will be developed and consistently applied to each of four coupled model?s long control runs to characterize their oceanic FW and heat budgets and assess underlying mechanisms of variability. The working hypothesis is that the recently observed changes in North Atlantic FW content reflect natural variability in this part of the climate system. Moreover, there are times when FW content plays an indirect or ?passive? role in the North Atlantic (i.e. the atmospheric forcing controls the ocean FW content and circulation variability); while at other times, salinity directly influences the circulation (i.e. increased (decreased) high latitude FW content weakens (intensifies) the sub-polar ocean circulation).Scientific Merit: By comparing several well-respected coupled climate model simulations and observations in a consistent manner, the proposed work will clarify connections between volumetric FW anomalies in the sub-polar North Atlantic and strength of the full three-dimensional gyre and overturning circulations. It will provide new perspectives regarding the timescales and mechanisms of internal variability in a part of the climate system known to exhibit large fluctuations. It will also update the time series of observed FW and heat content changes in the North Atlantic, provide meaningful estimates of their uncertainties, and elucidate the degree to which the recently observed fluctuations fall within the range of natural variability or alternatively reflect a consequence of some other forcing.Broader Impacts: The proposed work aims to develop and promote a set of diagnostic tools which will consistently and efficiently evaluate property content and ocean circulation in various coupled model simulations. These tools may be extended to other parts of the global ocean. They may also help to identify strengths and weaknesses in models? representations of processes, parameterizations and feedbacks. Construction of climatology products with spatial error covariances will better constrain the uncertainty in estimates of heat and FW content variability with substantial impact on how these are interpreted. Development of software, which will apply Gauss-Markov techniques to estimating mean and error covariance fields in the proposed North Atlantic work, can then readily be applied to global hydrographic climatologies. Assimilation efforts such as ECCO (?Estimating the Circulation and Climateof the Ocean?) will benefit directly because, for the purpose of state estimation, knowledge of the spatial error covariance is essential; yet this remains incompletely (or not at all) addressed within most available climatology products.This project is a contribution to the U.S. CLIVAR (CLImate VARiability and predictability) Program and the Ocean Research Priorities Plan (near-term priority on the Atlantic Meridional Overturning Circulation).

观察性记录表现出清晰的幅度证据，是亚极性淡水（FW）存储和GYRE强度的多年多年变异性的证据，但几乎不足以测量一个50年的周期。大西洋子午翻转循环（AMOC）已直接测量更少的时间，肯定不足以识别相关行为。大量的观察和模型研究集中在该主题的各个方面，但尚未对海洋系统的这一部分运作的统一描述。观察到的北大西洋FW内容和循环变异性的原因和后果的解释范围不同，促使他们试图更好地整理它们。提出了一项模型？数据与比较研究，哪个将研究FW内容的时机，幅度和可变性，相对于北大西洋的整个三维（GYRE和翻转）循环变异性和性质通量。将开发一套分析指数，并始终应用于四个耦合模型的长期控制跑步中的每个索引，以表征其海洋FW和热预算，并评估可变性的潜在机制。工作假设是，最近观察到的北大西洋FW含量的变化反映了气候系统这一部分的自然变异性。此外，有时FW内容扮演间接还是被动？在北大西洋中的作用（即大气强迫控制海洋FW含量和循环变异性）；虽然在其他时候，盐度直接影响循环（即高纬度fW含量的增加（减少）弱化（加强）亚极性海洋循环）。得出的优点：通过比较良好的耦合的气候模型模拟和观察结果，以一致的方式阐明了较高的连接，而较高的距离将阐明三分之一的连接。回旋和推翻循环。它将提供有关已知会表现出很大波动的一部分气候系统中内部变异性的时间标准和机制的新观点。它还将更新北大西洋观察到的FW和热量含量变化的时间序列，提供有意义的估计，并阐明最近观察到的波动在自然变异性范围内或替代的程度，或者反映了其他强迫的影响。BROADER的影响：提出的各种范围旨在开发和促进诊断的工具，并有效地促进了一致的型号，并有效地促进了一致的型号，并有效地进行了效率，并有效地进行了效率，并有效地进行了效率，并有效地进行了效率的效果。模拟。这些工具可以扩展到全球海洋的其他部分。他们还可能有助于确定模型中的优势和劣势吗？过程，参数化和反馈的表示。具有空间误差协方差的气候产物的构建将更好地限制热量和FW内容变异性的估计，并对解释方式的解释产生重大影响。然后，可以将软件的开发应用于估算拟议的北大西洋工作中的均值和错误协方差领域的高斯 - 马尔科夫技术，然后很容易地应用于全球水文气候。 ECCO等同化工作（估计海洋的循环和气候？）将直接受益，因为为了进行国家估算，对空间误差协方差的了解至关重要；然而，在大多数可用的气候产品中，这仍然不完全解决（或根本没有）。该项目是对美国克里瓦尔（气候可变性和可预测性）计划的贡献和海洋研究优先级计划（大西洋子午线翻倒循环的近期优先级）。