Mesoscale to submesoscale transition in the California current system. Part II: Frontal processes
Mesoscale to submesoscale transition in the California current system. Part II: Frontal processes
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DOI：
10.1175/2007jpo3672.1
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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.
这是三篇论文中的第二篇，这三篇论文研究了理想的、平衡的、副热带的、东部边界的、类似加州海流的上升流系统的数值模拟中发生的体制转换。从现象学和动力学的角度分析了新出现的高空大洋次中尺度锋面，采用了综合平均和分离不同流动亚区的方法。这一转变的初始动力过程是近地表锋生。锋面行为类似于观测到的气象面锋和被称为表面动力学(即均匀内部位涡Q和诊断力平衡)的近似动力学模式的解，即对中尺度应变场响应的表面密度梯度和次生环流的强化。然而，与表面动力学模型相比，存在显著的行为差异。风应力通过非线性Ekman输送和位涡的产生和破坏作用于锋面。应变诱导的锋生被强烈的亚中尺度锋面不稳定所破坏，进而导致次生锋生事件、亚中尺度涡旋和更小尺度气流的激发。在强烈的锋生和锋面不稳定事件中，地转和梯度风平衡发生了间歇性的亚中尺度破裂。
This is the second of three papers investigating the regime transition that occurs in numerical simulations for an idealized, equilibrium, subtropical, eastern boundary, upwelling current system similar to the California Current. The emergent upper-ocean submesoscale fronts are analyzed from phenomenological and dynamical perspectives, using a combination of composite averaging and separation of distinctive subregions of the flow. The initiating dynamical process for the transition is near-surface frontogenesis. The frontal behavior is similar to both observed meteorological surface fronts and solutions of the approximate dynamical model called surface dynamics (i.e., uniform interior potential vorticity q and diagnostic force balance) in the intensification of surface density gradients and secondary circulations in response to a mesoscale strain field. However, there are significant behavioral differences compared to the surface-dynamics model. Wind stress acts on fronts through nonlinear Ekman transport and creation and destruction of potential vorticity. The strain-induced frontogenesis is disrupted by vigorous submesoscale frontal instabilities that in turn lead to secondary frontogenesis events, submesoscale vortices, and excitation of even smaller-scale flows. Intermittent, submesoscale breakdown of geostrophic and gradient-wind force balance occurs during the intense frontogenesis and frontal-instability events.