Parameterization of tracer transport by geostrophic eddies in the southern ocean

涡旋扩散是由与海洋涡旋相关的湍流过程引起的实际混合，其变化范围从瞬态微尺度（cm）到稳定特征（数百km），如副热带环流甚至半球尺度流。海洋环流的涡旋成分，显然是一级混合项，并不是由气候模式通常预测的风应力强迫直接驱动的。一个问题出现了——涡流产生的横向混合如何被参数化？本文将研究一种利用残差平均公式改进广泛使用的南大洋粗分辨率海洋气候模式（MITgcm）的方法，其中涡旋位涡通量作为残差平均动量方程中的强迫项出现。残差平均理论的先前应用表明，在涡流和平均流以相同速度移动的临界水平附近，涡流扩散系数(K)的值增强。由此产生的模型将用于更好地理解和更可靠地预测的一些科学问题是：（一）南大洋及其经向翻转环流对盛行风变化和更广泛意义上的气候变化的响应；（二）海气热通量、二氧化碳通量、生物地球化学通量的相关变化，包括南大洋能够深层储存人为碳的能力；（三）海洋示踪剂运输如何取决于南大洋的基本物理、动力学和生物地球化学。

Abstract Eddy diffusion is the actual mixing caused by turbulent processes associated with ocean eddies, which vary from transient microscales (cm) to stable features (hundreds of km) such as subtropical gyres or even hemispheric scale currents. The eddy component of the ocean circulation, clearly a first order mixing term, is not directly driven by the wind stress forcings that climate models typically project. A problem arises - how can the lateral mixing produced by eddies be parameterized? An approach to improving a widely used coarse resolution ocean climate model (MITgcm) of the Southern Ocean using a residual-mean formulation in which eddy potential vorticity fluxes appear as forcing terms in the residual-mean momentum equations, will be investigated. Prior application of residual-mean theory has suggested that values of the eddy diffusivity (K) is enhanced in the vicinity of critical levels where eddies and mean flows move at the same speed. Some scientific problems that the resulting model will be used to better understand and more reliably predict are: (i) the response of the Southern Ocean and its meridional overturning circulation to changes in prevailing winds and in the larger sense changing climate(ii) associated changes in the air-sea flux of heat, CO2, biogeochemical fluxes, including the ability of the Southern Ocean to enable the deep storage of anthropogenic carbon (iii) how ocean tracer transports depend on the underlying physics, dynamics and biogeochemistry of the Southern Ocean.