The Interaction of Two Surface Vortices Near a Topographic Slope in a Stratified Ocean
The Interaction of Two Surface Vortices Near a Topographic Slope in a Stratified Ocean
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层状海洋中地形坡度附近两个表面涡旋的相互作用
DOI：
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发表时间：
2017
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影响因子：
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通讯作者：
J. Reinaud
中科院分区：
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作者：
C. Marez;X. Carton;Mathieu Morvan;J. Reinaud
在一个两层准地转模式中，我们研究了海底地形对两个相同涡旋相互作用的影响。这两个涡旋具有分段均匀的位涡，位于模式的上层。地形是一个平坦的底坡。对于两个气旋，地形改变了合并临界距离和合并效率：地形波动和涡旋可以使两个气旋在最初远离它时沿大陆架平流，或在它们最初靠近它时向大陆架平流。它们还可以使两个气旋相互平流，从而有利于合并。气旋发生变形，势涡场经历细丝。然后观察到部分涡旋合并或涡旋分裂的区域。分析了两层涡度极点的相互作用，解释了两个上层气旋的演变。对于较高的地形，出现了两个新的机制：涡旋漂移和分裂；以及丝状和不对称合并。它们是由于下层涡度与上层涡旋(赫顿是斜压涡偶极子，携带热量和动量并在流体中水平传播)的heton耦合，或由于前者对后者施加的强剪切所致。两个反气旋的相互作用表现为共转或合并的形式，但具体而言，它导致两个涡旋通过与低层相反符号涡度的异调耦合而远离斜坡。这种涡度起源于地形波的破碎。被动示踪剂演化的分析证实了流体的近岸或离岸漂移，沿着细丝形成示踪剂锋面，并在涡旋合并区进行搅动。粒子的轨迹表明了最初在漩涡中的流体最终是如何被分配的。
We study the influence of bottom topography on the interaction of two identical vortices in a two-layer, quasi-geostrophic model. The two vortices have piecewise-uniform potential vorticity and are lying in the upper layer of the model. The topography is a smooth bottom slope. For two cyclones, topography modifies the merger critical distance and the merger efficiency: the topographic wave and vortices can advect the two cyclones along the shelf when they are initially far from it or towards the shelf when they are initially closer to it. They can also advect the two cyclones towards each other and thus favour merger. The cyclones deform, and the potential vorticity field undergoes filamentation. Regimes of partial vortex merger or of vortex splitting are then observed. The interaction of the vorticity poles in the two layers are analysed to explain the evolution of the two upper layer cyclones. For taller topography, two new regimes appear: vortex drift and splitting; and filamentation and asymmetric merger. They are due to the hetonic coupling of lower layer vorticity with the upper layer vortices (a heton is a baroclinic vortex dipole, carrying heat and momentum and propagating horizontally in the fluid), or to the strong shear that the former exerts on the latter. The interaction of two anticyclones shows regimes of co-rotation or merger, but specifically, it leads to the drift of the two vortices away from the slope, via a hetonic coupling with oppositely-signed vorticity in the lower layer. This vorticity originates in the breaking of the topographic wave. The analysis of passive tracer evolution confirms the inshore or offshore drift of the fluid, the formation of tracer fronts along filaments and its stirring in regions of vortex merger. The trajectories of particles indicate how the fluid initially in the vortices is finally partitioned.