Eddy-driven transports in the Antarctic Circumpolar Current

在南大洋，涡流驱动的运输量可能与平均运输量一样大。特别是经向、跨锋面输送受中尺度涡旋活动的影响甚至控制。另一方面，这些运输将南大洋设定为全球碳循环中一个主要的海洋汇。在海洋模型中，这种可变性必须得到充分的解决或参数化。Gent和McWilliams(1990)的参数化法目前被用来解释这种涡流驱动的输运，其中必须指定所谓的厚度扩散系数K。目前已知的K只有大约1个数量级，但特别是在南大洋，K的选择对质量和示踪剂的经向输送有很大影响，因此对量化南大洋在气候系统和全球碳循环中的作用至关重要。建议从现有的涡旋分辨海洋模式的合成数据中估算南大洋的厚度扩散系数K。虽然以前的尝试强调了旋转涡旋通量的问题，这使得估算过程变得复杂，但最近的研究表明，定义和使用物理上有意义的旋转通量可以减少这一问题。因此，对南大洋K的可靠估计似乎首次成为可能。此外，建议估计海洋模式预测的平均值和厚度扩散系数之间的关系，这是建立自洽的涡旋参数化所必需的。

In the Southern Ocean, eddy-driven transports can be as large as mean transports. In particular the meridional, cross frontal transports are affected or even controlled by meso-scale eddy activity. On the other hand, these transports set the role of the Southern Ocean as a major oceanic sink in the global carbon cycle. In ocean models, such variability has to be adequately resolved or parameterised. The parameterisation by Gent and McWilliams (1990) is currently used to account for such eddy-driven transports, in which the so-called thickness diffusivity K has to be specified. Only a rough order of I magnitude is currently known for «, but, in particular in the Southern Ocean, the choice of K strongly affects meridional transports of mass and tracers and is therefore of crucial importance to quantify the role of the Southern Ocean in the climate system and the global carbon cycle. It is proposed to estimate the thickness diffusivity K in the Southern Ocean from synthetic data of an existing realistic eddy-resolving ocean model. While previous attempts highlight the problem of rotational eddy fluxes which complicate the estimation procedure, it has been recently shown that the definition and use of physically meaningful rotational fluxes reduces this problem. Therefore, reliable estimates of K in the Southern Ocean appear possible for the first time. Furthermore, it is proposed to estimate relations between mean quantities predicted by ocean models and thickness diffusivity, necessary in order to build a self-consistent eddy parameterisation.