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).

观测记录清楚地表明，副极地淡水（FW）储存量和环流强度存在大幅度的、年代际至数十年的变化，但其长度不足以测量单个 50 年周期。直接测量大西洋经向翻转环流（AMOC）的时间甚至更短，而且肯定不足以识别相关行为。大量的观测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如何运作产生统一的认识。对观测和模拟的北大西洋 FW 含量和环流变化的原因和后果有不同的解释，这促使人们尝试更好地对它们进行分类。提出了模型数据比对研究，该研究将调查与北大西洋完整三维（环流和翻转）环流变化和属性通量相关的 FW 内容的时间、幅度和变化。将开发一套分析指数，并将其一致地应用于四个耦合模型的长期控制运行中的每一个，以表征其海洋 FW 和热量预算，并评估潜在的变异机制。工作假设是，最近观察到的北大西洋 FW 含量变化反映了这部分气候系统的自然变化。此外，有时固件内容会起到间接或“被动”的作用。在北大西洋的作用（即大气强迫控制海洋 FW 含量和环流变化）；而在其他时候，盐度直接影响环流（即增加（减少）高纬度 FW 含量会削弱（增强）副极地海洋环流）。 科学优点：通过比较几个备受推崇的耦合气候模型模拟和观测结果，得出一致的结果以这种方式，拟议的工作将澄清北大西洋副极地的体积FW异常与完整三维环流和翻转环流的强度之间的联系。它将提供关于已知表现出较大波动的气候系统部分的时间尺度和内部变化机制的新视角。它还将更新北大西洋观测到的 FW 和热含量变化的时间序列，对其不确定性提供有意义的估计，并阐明最近观测到的波动在自然变率范围内的程度，或者反映某些因素的后果。其他强迫。更广泛的影响：拟议的工作旨在开发和推广一套诊断工具，这些工具将一致有效地评估各种耦合模型模拟中的财产内容和海洋环流。这些工具可能会扩展到全球海洋的其他地区。它们还可能有助于识别模型的优点和缺点？过程、参数化和反馈的表示。构建具有空间误差协方差的气候学产品将更好地限制热量和固件含量变化估计的不确定性，并对这些变化的解释产生重大影响。软件的开发将应用高斯-马尔可夫技术来估计拟议的北大西洋工作中的均值和误差协方差场，然后可以很容易地应用于全球水文气候学。 ECCO（？估计海洋环流和气候？）等同化工作将直接受益，因为为了状态估计的目的，空间误差协方差的知识至关重要；然而，大多数可用的气候学产品仍然没有完全（或根本没有）解决这个问题。该项目是对美国 CLIVAR（气候变化和可预测性）计划和海洋研究优先计划（大西洋经向翻转环流的近期优先事项）的贡献）。