Tilted Baroclinic Tidal Vortices

Abstract

The structure of baroclinic vortices generated by horizontal flow separation past a sloping headland in deep, stably stratified waters is investigated. The most distinctive feature of these eddies is that their cores are strongly tilted with respect to the stratification, yet their velocity field remains quasi-horizontal. Field observations and numerical simulations are used to explore the consequences of the strong tilt on the eddy baroclinic structure. It is found that the background density field is altered in such a way as to maintain a pressure minimum in the tilted vortex cores. This adjustment results in a fundamental asymmetry of the density field. Isopycnals are deflected upward on the shoreward side and downward on the opposite side of the eddy center. The resulting pattern closely resembles the asymmetries of azimuthal wavenumber one that develop when tropical cyclones become tilted by an environmental shear. The authors provide a simple analytical model that suggests this structure is obtained via a balance between the centrifugal force and the horizontal pressure gradient. As the eddies release from the boundary, adjust, and decay, their tilt as well as the associated density perturbation decrease and lose coherence. It is suggested that this may lead to a conversion of potential energy into kinetic energy.