This paper examines factors contributing to the remarkable longevity of coherent vortices in the subtropical westward flows. Baroclinic vortices embedded in large-scale vertical shears generate Rossby waves which form an opposite sign eddy associated with inertial Taylor columns on the beta-plane. The combination of the vortex and lee Rossby wave can be viewed as a hetonic dipole that induces meridional drift and heat flux leading to self-amplification of vortices in baroclinically unstable flows. The analytical tractability is achieved by considering the marginally stable flow, where the beta-effect is nearly compensated by the potential vorticity gradient (PVG) associated with the meridional slope of the density interface. In the two-layer model such compensation can occur in the upper layer with the westward flow or in the lower layer with the eastward flow on top. In baroclinically unstable mean flows, vortices are shown to intensify due to the Lagrangian conservation of potential vorticity inside their cores, drifting meridionally in the layer with negative PVG and supporting baroclinic turbulence. The theory is confirmed by numerical simulations indicating that for westward flows in subtropical oceans, reduced PVG in the upper layer provides favorable conditions for eddy longevity and pathways.

本文研究了导致副热带西向流动中相干涡旋显着延长寿命的因素。嵌在大型垂直切变中的斜压涡流产生Rossby波，形成与β平面上惯性泰勒柱相关的相反符号涡。涡流和lee Rossby波的组合可以看作是一个高音偶极子，它引起子午漂移和热通量，从而导致斜压不稳定流中涡流的自放大。通过考虑边缘稳定的流动来实现分析可处理性，其中，β效应几乎被与密度界面的子午坡度相关的潜在涡度梯度（PVG）所补偿。在两层模型中，这种补偿可以在向西流动的上层或在向东流动的下层发生。在斜压不稳定的平均流量中，由于拉格朗日核心内的潜在涡度守恒，在负PVG的层中子午线地漂移并支持斜压湍流，涡流显示出加剧的趋势。数值模拟证实了该理论，表明对于亚热带海洋的西向流动，上层的PVG降低为涡旋寿命和路径提供了有利条件。