Mesoscale to submesoscale transition in the California current system. Part I: Flow structure, eddy flux, and observational tests
Mesoscale to submesoscale transition in the California current system. Part I: Flow structure, eddy flux, and observational tests
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DOI：
10.1175/2007jpo3671.1
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发表时间：
2008-01-01
影响因子：
3.5
通讯作者：
Shchepetkin, A. F.
中科院分区：
文献类型：
--
作者：
Capet, X.;Mcwilliams, J. C.;Shchepetkin, A. F.
在一个理想化的副热带东边界上升流系统（类似于加州海流）的数值模拟中，当水平网格尺度减小到O（1）km时，涡动变率发生了一个亚中尺度的转变。这第一篇论文（在一系列的三个）描述的过渡方面的紧急流动结构和相关的时间平均涡通量。除了由沿岸的主要不稳定性、风驱动的海流引起的中尺度涡旋之外，大量能量被转移到海洋上层的次中尺度锋面和涡旋中。次中尺度是通过表面锋生产生的，这些锋生是从上涌的冷丝中产生的，这些冷丝被拉到海上，并在中尺度涡旋中心之间产生应变。反过来，一些次中尺度锋变得不稳定，发展出次中尺度曲流，并分裂成卷起的涡旋。与这种现象相联系的是大的垂直涡度和Rossby数，大的垂直速度，相对平坦的水平谱（与中尺度动力学的流行观点相反），大的垂直浮力通量起着抑制上层海洋的作用，亚中尺度能量从势能到动能的转换，上层海洋中显著的时空不稳定性，以及表层边界层与密度跃层之间的物质交换。与现有观测结果的比较表明，次中尺度锋和不稳定性在上层海洋广泛存在，其特征与模拟相似。
In computational simulations of an idealized subtropical eastern boundary upwelling current system, similar to the California Current, a submesoscale transition occurs in the eddy variability as the horizontal grid scale is reduced to O(1) km. This first paper (in a series of three) describes the transition in terms of the emergent flow structure and the associated time-averaged eddy fluxes. In addition to the mesoscale eddies that arise from a primary instability of the alongshore, wind-driven currents, significant energy is transferred into submesoscale fronts and vortices in the upper ocean. The submesoscale arises through surface frontogenesis growing off upwelled cold filaments that are pulled offshore and strained in between the mesoscale eddy centers. In turn, some submesoscale fronts become unstable and develop submesoscale meanders and fragment into roll-up vortices. Associated with this phenomenon are a large vertical vorticity and Rossby number, a large vertical velocity, relatively flat horizontal spectra (contrary to the prevailing view of mesoscale dynamics), a large vertical buoyancy flux acting to restratify the upper ocean, a submesoscale energy conversion from potential to kinetic, a significant spatial and temporal intermittency in the upper ocean, and material exchanges between the surface boundary layer and pycnocline. Comparison with available observations indicates that submesoscale fronts and instabilities occur widely in the upper ocean, with characteristics similar to the simulations.