Collision of anticyclonic, lens‐like eddies with a meridional western boundary

Abstract

The collision of anticyclonic, lens‐like eddies with a meridional western boundary is investigated as a function of two independent, nondimensional numbers: β = β0R/f0 and ε = ω/f0, where f0 and β0 are the Coriolis parameter and its rate of change with latitude, respectively, both evaluated at the reference latitude. R is the eddy's radius, and ω is its angular frequency. The numerical experiments show that in all cases there is a southward expulsion of mass proportional to both β and ε. which is estimated during the eddy‐boundary interaction. The eddies are invariably deformed with the initial collision, but afterward, they reacquire a new circular shape. There is a meridional translation of the eddy along the boundary which depends exclusively on the initial ratio r = ε/β. If r>1, the eddy goes southward, but if r<1, the eddy goes northward first and then southward. As the eddy loses mass and reacquires a new circular shape, there is a readjustment of β and ε such that β decreases because its radius becomes smaller and ε increases by energy conservation. This implies that the eddies ultimately migrate southward. A formula, derived for the meridional speed of the center of mass of the eddy is consistent with the numerical results. A physical interpretation shows that after collision a zonal force is exerted on the eddy by the wall which is balanced by a meridional migration. Nonlinearities induce a southward motion, while high β values could produce northward motion, depending on the mass distribution along the wall.