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首页> 外文期刊>Journal of Physical Oceanography >The Role of Horizontal Divergence in Submesoscale Frontogenesis
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The Role of Horizontal Divergence in Submesoscale Frontogenesis

机译：水平散度在亚中尺度额叶形成中的作用

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Oceanic surface submesoscale currents are characterized by anisotropic fronts and filaments with widths from 100 m to a few kilometers; an O(1) Rossby number; and large magnitudes of lateral buoyancy and velocity gradients, cyclonic vorticity, and convergence. We derive an asymptotic model of submeoscale frontogenesis-the rate of sharpening of submesoscale gradients-and show that in contrast with "classical" deformation frontogenesis, the near-surface convergent motions, which are associated with the ageostrophic secondary circulation, determine the gradient sharpening rates. Analytical solutions for the inviscid Lagrangian evolution of the gradient fields in the proposed asymptotic regime are provided, and emphasize the importance of ageostrophic motions in governing frontal evolution. These analytical solutions are further used to derive a scaling relation for the vertical buoyancy fluxes that accompany the gradient sharpening process. Realistic numerical simulations and drifter observations in the northern Gulf of Mexico during winter confirm the applicability of the asymptotic model to strong frontogenesis. Careful analysis of the numerical simulations and field measurements demonstrates that a subtle balance between boundary layer turbulence, pressure, and Coriolis effects (e.g., turbulent thermal wind; Gula et al. 2014) leads to the generation of the surface convergent motions that drive frontogenesis in this region. Because the asymptotic model makes no assumptions about the physical mechanisms that initiate the convergent frontogenetic motions, it is generic for submesoscale frontogenesis of O(1) Rossby number flows.
机译：海洋表面亚中尺度水流的特征是各向异性的锋面和宽度从100 m到几千米的细丝。 O（1）Rossby数；以及较大的横向浮力和速度梯度，气旋涡度和会聚。我们推导了一个亚尺度尺度前生的渐近模型（亚尺度尺度梯度的锐化速率），并表明与“经典”形变前沿发生相反，近地层收敛运动与年龄变质次生环流有关，决定了梯度锐化率。提供了在拟议的渐进状态下梯度场的无粘性拉格朗日演化的解析解，并强调了年龄变迁运动在控制额叶演化中的重要性。这些分析解决方案还用于导出与梯度锐化过程相伴的垂直浮力通量的比例关系。冬季在墨西哥湾北部的逼真的数值模拟和漂流观测证实了渐近模型对强锋生的适用性。对数值模拟和现场测量结果的仔细分析表明，边界层湍流，压力和科里奥利效应（例如，湍流热风； Gula等人，2014）之间的微妙平衡导致了表面收敛运动的产生，这些运动推动了前锋的形成。这个地区。因为渐近模型不对引发收敛的前生运动的物理机制做出任何假设，所以它对于O（1）Rossby数流的亚中尺度前生是通用的。

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