Topographic effects on the anticyclonic vortex evolution: A modeling study

Abstract

The evolution of anticyclonic vortices in the presence of topographic effects associated with continental slope steepness and orientation is investigated using the Hybrid Coordinate Ocean Model. The trajectories of the vortices are analyzed using various configurations of slope steepness and orientation, including a flat bottom. As the steepness of the slope is increased, the development and evolution of a counter-rotating subsurface vortex (‘deep cyclone’) is strongly dispersive resulting in strong zonal translation over the slope, although the translation is southwest with a coherent deep cyclone, in the flat bottom case. In particular, the zonal translation is faster with a gentle slope (relative to the flat bottom case) due to an upslope tilt of the deep cyclone. As the surface vortex collides with the steep topography, the deflection angle increases as the slope increases (i.e. it deflects along slope) at the same time the bottom vorticity peaks, generating a ‘collision’ cyclone and a slope jet south of the vortex-slope impact. In the realistic steep slope case, along slope translation is dominant when the vortex departs over/near the slope, although the vortex strongly collides with (and rapidly crosses) the slope if it has strong westward inertia. During the cross-slope translation, vorticity restoration by vortex compression occurs with relatively small poleward translation. At the point of maximum bottom vorticity, rapid vortex erosion occurs horizontally and vertically, and southwestward translation is restored. Comparison of vortex translation over four different slope orientations suggests that the vortex is strongly affected by the location of adjacent cyclones which tend to propagate onshore and poleward simultaneously, and that the combined planetary and topographic β-effect slows the vortex translation on the northern slope.