Decadal and multi-decadal ocean memory in the eddying regime

十年尺度的气候预测已被证明是难以捉摸的。在这些时间尺度上，由于人为气候强迫，气候系统的自然混乱变异性主导着更可预测的趋势。耦合的大气环流模式结果之间的差异令人沮丧，并指出空间分辨率缺乏收敛和物理参数化不充分。气候系统的观测记录持续时间较短，特别是海洋和冰冻圈的观测记录持续时间较短，阻碍了对十年时间尺度的可靠统计分析。冬季海洋温度异常的周期性重现是一年以上尺度上可预报性的潜在来源。为了使这一机制提供与大气的强有力的相互作用，海洋温度异常必须经受住季节性循环和等轴线上的涡流搅动。推测在比涡旋尺度更大的尺度上，温度扰动可以幸免于等轴涡旋搅动。必须确定能够承受季节性循环的扰动的阈值、幅度和持续时间(或持续性)。智力上的优点：该项目将确定大西洋中可以增强热带以外地区年代际可预报性的区域。对涡旋区域绝热次表层流动的关注将补充研究扩散的、高度阻尼的海洋动力学的传统方法，并将确定最强大的海洋物理过程，以便在十年尺度上进行预测。之所以选择大西洋，是因为在这个地区，自然时间尺度是十年制的，通过风旋动力学是十年制的，而通过极地翻转环流是几十年制的。由于中尺度涡旋决定了次温跃层海洋层结，从而决定了海洋的热量输送，因此在涡旋状态下工作是必要的。此外，在高分辨率下，衰减降低，从而允许大的区域梯度和更长的影响持续时间：这两者都是强大的大气印记所必需的要素。方法是使用几个跨越一系列复杂性的海洋模式：带有参数化斜压涡旋的粗分辨率正演和伴随模式，以及涡旋分辨率模式。更广泛的影响：超过一个季节和热带以外地区的气候信息的经济和社会效益怎么强调都不为过。中纬度和高纬度海洋过程有可能为十年预报提供技能，它们是本提案的重点。研究生和职业生涯初期的科学家将丰富他们在物理海洋学、气候动力学和科学方法方面的知识，并接受数学、数值模拟和现代科学计算方面的培训。初中和高中教师讲习班将有助于让新一代公民了解气候科学的成就、局限性和未来前景。

Climate predictions on decadal scales have proven elusive. On these time-scales, the natural chaotic variability of the climate system dominates over the more predictable trends due to anthropogenic climate forcing. The differences among coupled general circulation models results are discouraging, and point to a lack of convergence in spatial resolution and to inadequate physical parameterizations. The difficulty is compounded by the short duration of observational records of the climate system, particularly those of the ocean and cryospherewhich hinders robust statistical analysis on decadal time scales.A leading candidate for pockets of predictability in selected regions resides in the memory intrinsic in the slow, almost adiabatic evolution of the ocean below the mixed layer. The periodic reemergence of oceanic temperature anomalies in winter is a potential source of predictability on scales longer than one year. In order for this mechanism to provide robust interaction with the atmosphere, ocean temperature anomalies must survive the seasonal cycling and the eddy stirring on isopycnals. It is conjectured that temperature perturbations on scales larger than the eddy size survive isopycnal eddy stirring. The threshold amplitude and duration (or persistence) of perturbation that can withstand the seasonal cycling must be determined.Intellectual Merit: This project will identify the regions in the Atlantic Ocean that can enhance decadal predictability in the extra-tropics. The focus on adiabatic subsurface flow in the eddying regime will complement the traditional approach of studying diffusive, highly damped oceanic dynamics, and will identify the most robust oceanic physical processes for prediction at decadal scales. The Atlantic Ocean is chosen because in this region the natural time scales are decadal, through the wind-gyres dynamics, and multi-decadal, through the pole-to-pole overturning circulation. It is essential to work in the eddying regime, because mesoscale eddies determine the sub-thermocline oceanic stratification and thus the oceanic heat transport. Furthermore, at high resolution, damping is reduced allowing large regional gradients and longer duration of influence: both are necessary elements for robust atmospheric imprinting. The approach is to use several ocean models spanning a range of complexities: coarse resolution forward and adjoint models both with parameterized baroclinic eddies, and a model at eddy-resolution.Broader Impacts: The economical and social benefits of climate information for periods longer than a season and regions beyond the tropics cannot be overstated. Mid- and high-latitude ocean processes have the potential to provide skill to decadal forecasts, and they are the focus of this proposal. A graduate student and an early-career scientist will enrich their knowledge in physical oceanography, climate dynamics and the scientific method, and be trained in mathematics, numerical modeling and modern scientific computations. A middle and high school teacher workshop will contribute to informing the new generation of citizens on the achievements, limitations and future prospects of climate science.