下一阶平衡模型捕捉亚中尺度物理与统计特征
Next-order balanced model captures submesoscale physics and statistics
AI总结：
本文通过非线性模拟证明基于位涡的下一阶Rossby平衡模型QG+1能捕捉海洋亚中尺度物理特征，包括气旋尾部、非地转锋面及锋生爆破，且反演简单，是研究上层海洋亚中尺度动力学的有效工具。
摘要：
通过在两种设置下的非线性模拟，我们证明了QG$^\mathrm{+1}$——一种基于位涡的下一阶Rossby平衡模型——能够捕捉海洋亚中尺度物理的多个方面。在斜压不稳定的Eady型背景态下的强迫-耗散三维模拟中，统计平衡湍流表现出长的气旋性尾部和大量快速增强的非地转锋面。尽管该模型需要为固定的尺度化Rossby数设定一个显式的小值，但涌现的流动仍以大于局地Coriolis频率的涡度和辐合值为特征，正如在上层海洋亚中尺度流中所观测到的那样。在经典的应变诱导锋生设置下对QG$^\mathrm{+1}$的模拟显示出真实的锋面不对称性和可证明的有限时间爆破，在定量上与半地转方程的模拟相当。QG$^\mathrm{+1}$模型中的反演是直接的线性Poisson问题，允许从位涡和表面浮力重建所有流场，同时避免了半地转坐标变换。综合来看，这些结果表明QG$^\mathrm{+1}$可能是研究上层海洋亚中尺度动力学的有用工具。
英文摘要：
Using nonlinear simulations in two settings, we demonstrate that QG$^\mathrm{+1}$, a potential-vorticity based next-order-in-Rossby balanced model, captures several aspects of ocean submesoscale physics. In forced-dissipative 3D simulations under baroclinically unstable Eady-type background states, the statistical equilibrium turbulence exhibits long cyclonic tails and a plethora of rapidly-intensifying ageostrophic fronts. Despite that the model requires setting an explicit, small value for the fixed scaling Rossby number, the emergent flows are nevertheless characterized by vorticity and convergence values larger than the local Coriolis frequency, as observed in upper-ocean submesoscale flows. Simulations of QG$^\mathrm{+1}$ under the classic strain-induced frontogenesis set-up show realistic frontal asymmetry and a provable finite time blow-up, quantitatively comparable to simulations of the semigeostrophic equations. The inversions in the QG$^\mathrm{+1}$ model are straightforward linear Poisson problems, allowing for the reconstruction of all flow fields from the PV and surface buoyancy, while avoiding the semigeostrophic coordinate transformation. Taken together, these results suggest QG$^\mathrm{+1}$ might be a useful tool for studying upper-ocean submesoscale dynamics.
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