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).

观测记录清楚地证明了亚极地淡水储存和涡旋强度的大幅度、十年到几十年的变化，但其长度几乎不足以测量一个50年的周期。直接测量大西洋子午线翻转环流(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侧重于这一专题的各个方面，但尚未就海洋系统的这一部分如何运作产生一个统一的图景。对观测和模拟的北大西洋FW含量和环流变异性的原因和后果的不同解释促使人们试图更好地对它们进行分类。本文提出了一项模式资料对比研究，将研究FW含量的时间、幅度和变率与北大西洋全三维(涡旋和翻转)环流变率和特征通量的关系。将开发一套分析指数，并一致地应用于四个耦合模式-S长控制运行的每一个，以表征它们的海洋FW和热量收支，并评估潜在的可变性机制。工作假设是，最近观察到的北大西洋FW含量的变化反映了这一部分气候系统的自然变异性。此外，FW内容有时会起间接或被动的作用。在北大西洋，盐度直接影响环流(即高纬度FW含量增加(减少)，削弱(加强)亚极地海洋环流)。科学价值：通过以一致的方式比较几个备受推崇的耦合气候模式模拟和观测，拟议的工作将澄清北极区体积FW异常与全三维涡旋和翻转环流强度之间的联系。它将为气候系统中一个已知表现出巨大波动的部分的内部可变性的时间尺度和机制提供新的视角。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多大程度上落在自然变化范围内，或者反映一些其他强迫的结果。广泛影响：拟议的工作旨在开发和促进一套诊断工具，在各种耦合模式模拟中一致和有效地评估属性含量和海洋环流。这些工具可能会扩展到全球海洋的其他部分。它们还可能有助于识别模型的优势和劣势？过程、参数和反馈的表示。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FW含量可变性估计的不确定性，并对如何解释这些内容产生重大影响。开发的软件将应用高斯-马尔可夫技术来估计拟议的北大西洋工作中的平均场和误差协方差场，然后可以很容易地应用于全球水文气候学。同化努力，如ECCO(？估计海洋的循环和气候？)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是必不可少的；然而，在大多数可用的气候学产品中，这一点仍然没有完全(或根本没有)得到解决。该项目是对美国CLIVAR(气候可变性和可预测性)计划和海洋研究优先计划(大西洋子午线颠覆环流的近期优先事项)的贡献。