Effects of a topographic gradient on coastal current dynamics

Abstract

When a boundary current in a rotating environment encounters a significant change in depth, two typical behaviors are observed. The flow may bifurcate, with one branch moving away from the boundary following the topographic contours and the other branch following the boundary. Alternatively, the boundary current may rebound or retroflect from the topography, with the formation of a dipole that moves in the upstream direction. Which behavior is observed is determined, for the most part, by the geometry of the system and not by the initial direction of the boundary current. Bifurcation is typical in a right-handed geometry, i.e., in the case with the boundary on the right side looking from deep to shallow water, while retroflection is typical in a left-handed geometry. Laboratory experiments in a rotating tank using dye visualization and particle tracking verify this basic dichotomy but also reveal new aspects of the problem not examined in previous studies. In particular, it is demonstrated that in the enclosed basin, there is a return current flowing counter to the branch following the topographic contours. The experimental design allows comparison of the large time flow with the circulation in the Adriatic Sea. Copyright 2005 by the American Geophysical Union.