Eddy Shape, Orientation, Propagation, and Mean Flow Feedback in Western Boundary Current Jets
Eddy Shape, Orientation, Propagation, and Mean Flow Feedback in Western Boundary Current Jets
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DOI：
10.1175/jpo-d-12-0152.1
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发表时间：
2013-08
影响因子：
3.5
通讯作者：
S. Waterman;B. Hoskins
中科院分区：
文献类型：
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作者：
S. Waterman;B. Hoskins
本文利用水平速度相关张量的性质，对西边界流扩展急流理想模型中的涡-平均流相互作用进行了研究，诊断了平均涡的形状、方向、传播和平均流反馈的特征，然后利用这些涡的特征对涡-平均流相互作用提供了一种新的解释。诊断显示模式的平均涡流的形状，方向和传播是一致的，在上游区域和下游区域的波辐射的射流不稳定的签名。它们一起对平均流提供反馈，该平均流提供射流的下游特性并驱动射流的再循环涡旋。将涡动强迫分解为单个项的贡献证实了纬向涡动倾斜中的横向急流梯度在稳定急流到正压不稳定性方面的预期作用;然而，它也揭示了涡动纬向伸长的沿急流演变所起的重要作用。这是来自这些模式的平均流强迫的作用，以加强和扩大下游的射流，并迫使时间平均再循环涡旋。这种理解的依赖平均流强迫涡结构特性表明，未能充分解决涡伸长可能会削弱射流强度，范围，并改变了再循环结构，在这个理想化的模型中看到的空间分辨率降低。此外，它可能会建议新的想法参数化的这种强迫。
This manuscript revisits a study of eddy‐mean flow interactions in an idealized model of a western boundary current extension jet using properties of the horizontal velocity correlation tensor to diagnose characteristics of averageeddyshape,orientation,propagation,andmeanflowfeedback.Theseeddycharacteristicsarethenused toprovideanewdescriptionoftheeddy‐meanflowinteractionsobservedintermsofdifferentingredientsofthe eddy motion. The diagnostics show patterns in average eddy shape, orientation, and propagation that are consistent with the signatures of jet instability in the upstream region and wave radiation in the downstream region. Together they give a feedback onto the mean flow that gives the downstream character of the jet and drives the jet’s recirculation gyres. A breakdown of the eddy forcing into contributions from individual terms confirms the expected role of cross-jet gradients in meridional eddy tilt in stabilizing the jet to its barotropic instability; however, it also reveals important roles played by the along-jet evolution of eddy zonal‐meridional elongation. It is the mean flow forcing derived from these patterns that acts to strengthen and extend the jet downstream and forces the time-mean recirculation gyres. This understanding of the dependence of mean flow forcing on eddy structural properties suggests that failure to adequately resolve eddy elongation could underlie the weakened jet strength, extent, and changed recirculation structure seen in this idealized model for reduced spatial resolutions. Further, it may suggest new ideas for the parameterization of this forcing.