A Theory of the Wind-Driven Beaufort Gyre Variability
A Theory of the Wind-Driven Beaufort Gyre Variability
复制标题
DOI：
10.1175/jpo-d-16-0091.1
复制
发表时间：
2016-11-01
影响因子：
3.5
通讯作者：
Thompson, Andrew F.
中科院分区：
文献类型：
--
作者：
Manucharyan, Georgy E.;Spall, Michael A.;Thompson, Andrew F.
博福特环流的盐跃层在年际到年代际的时间尺度上变化显著，影响着北冰洋的淡水含量。本研究探讨了涡旋在埃克曼驱动的环流变化中的作用。根据转换后的欧拉平均范式，作者发展了一种理论，将FWC的变化与大规模环流的稳定性联系起来，定义为其平衡时间的倒数。涡分辨数值模拟验证的理论，表明环流的稳定性是明确控制的中尺度涡扩散。精确表示盐跃层动态需要300 + 200 m（2）s（-1）的涡动扩散率，这低于大多数低分辨率气候模式中使用的涡动扩散率。特别是，在年际和更长的时间尺度上的涡动通量和Ekman泵提供同样重要的贡献FWC的变化。然而，只有大规模的埃克曼泵模式可以显着改变FWC，空间局部扰动是一个数量级的效率较低。最后，作者介绍了一种新的FWC趋势诊断的涡旋指数，可以很方便地计算使用的观测只位于沿着涡旋边界。其强大的预测能力，在涡解析模型随机风迫使评估，表明环流指数将用于解释FWC演变的观察，以及在数值模式。
The halocline of the Beaufort Gyre varies significantly on interannual to decadal time scales, affecting the freshwater content (FWC) of the Arctic Ocean. This study explores the role of eddies in the Ekman-driven gyre variability. Following the transformed Eulerian-mean paradigm, the authors develop a theory that links the FWC variability to the stability of the large-scale gyre, defined as the inverse of its equilibration time. The theory, verified with eddy-resolving numerical simulations, demonstrates that the gyre stability is explicitly controlled by the mesoscale eddy diffusivity. An accurate representation of the halocline dynamics requires the eddy diffusivity of 300 + 200 m(2) s(-1), which is lower than what is used in most low-resolution climate models. In particular, on interannual and longer time scales the eddy fluxes and the Ekman pumping provide equally important contributions to the FWC variability. However, only large-scale Ekman pumping patterns can significantly alter the FWC, with spatially localized perturbations being an order of magnitude less efficient. Lastly, the authors introduce a novel FWC tendency diagnostic-the Gyre Index-that can be conveniently calculated using observations located only along the gyre boundaries. Its strong predictive capabilities, assessed in the eddy-resolving model forced by stochastic winds, suggest that the Gyre Index would be of use in interpreting FWC evolution in observations as well as in numerical models.