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

观测记录显示出明显的证据，大幅度，十年到几十年的变化，在副极地淡水（FW）存储和环流强度，但几乎没有足够长的时间来测量一个单一的50年的周期。大西洋经向翻转环流（AMOC）直接测量的时间更短，当然也不足以识别相关行为。大量的观测和模型研究都集中在这一主题的各个方面，但尚未对海洋系统的这一部分如何运作产生统一的看法。对观测到的和模拟的北大西洋FW含量和环流变化的原因和后果的不同解释促使人们试图更好地整理它们。模特？数据相互比较研究的建议，这将调查的时间，幅度和FW含量的变化与全三维（环流和翻转）环流变率和财产通量在北大西洋。一套分析指数将开发和一贯适用于每一个四个耦合模型？的长期控制运行，以表征其海洋FW和热量收支，并评估潜在的变化机制。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率。此外，有些时候，FW内容发挥间接或？被动？在北大西洋的作用（即大气强迫控制海洋FW含量和环流变率）;而在其他时候，盐度直接影响环流（即高纬FW含量的增加（减少）减弱了（加强）副极地海洋环流）。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，拟议的工作将阐明北大西洋副极地的体积FW异常与全三维环流和翻转环流的强度之间的联系。它将提供新的视角，了解已知气候系统中表现出大幅度波动的一部分内部变率的时间尺度和机制。它还将更新观测到的北大西洋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属于自然变率的范围，或者反映了其他一些强迫的后果。拟议的工作旨在开发和推广一套诊断工具，这些工具将在各种耦合模型模拟中一致和有效地评估财产内容和海洋环流。这些工具可以推广到全球海洋的其他部分。它们还可能有助于确定模型的优点和缺点。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约束热量和FW含量变化估计的不确定性，并对如何解释这些变化产生重大影响。将高斯-马尔可夫技术应用于估计拟议的北大西洋工作中的平均和误差协方差场的软件的开发，可以很容易地应用于全球水文气候学。同化努力，如ECCO（？海洋环流和气候的估算？）将直接受益，因为，对于状态估计的目的，空间误差协方差的知识是必不可少的;然而，这仍然是不完全（或根本没有）解决在大多数可用的气候学products.This项目是对美国的贡献CLIVAR（气候变化和可预测性）计划和海洋研究优先计划（近期优先大西洋经向翻转环流）。

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).