Critical effects of a tall seamount on a drifting vortex

The initial-value problem for the evolution of an isolated vortex encountering a tall seamount during its westward beta-drift is studied within an equivalent-barotropic model, that is generalized to allow for the intersection of the layer interface with a sloping bottom. Given the Rossby radius and linear wave speed in the model, the parabolic shape of a seamount top and initial potential vorticity profile in the vortex core, the outcome is controlled by the vortex sign and a number of parameters: the seamount radius and height of penetration into the active layer, the radius and intensity of the vortex, the initial offset of the vortex center relative to the seamount, the Ekman layer depth over the seamount top, and the momentum lateral diffusion coefficient. Here we consider regimes for narrow seamounts where cyclonic vorticity generated in the water column swept off the top of the seamount plays a negligible role. The most significant effect on the vortex evolution is provided by a topographically induced anti-cyclonic circulation that is formed after squashing of water column replaced over the top of the seamount by the approaching vortex. The Geostrophic Vorticity intermediate model is used for numerical experiments. When the area of penetration is small and the topographic anticyclone is weak, the vortex drifts either predominantly westward north of the seamount or rotates around the seamount which is explained by presence of a separatrix in a simple kinematic model. For a larger area of penetration and stronger topographic anticyclone, violent interactions result in substantial deformations of the vortex core and loss of the material from the vortex periphery that leads to anomalous transport and diffusion. Vortex capture over the seamount is found in one range of parameters