The Generation and Evolution of Mushroom-like Vortices

Abstract

Numerical simulations have been performed to understand the generation and evolution of mushroom-like patterns observed in remote sensing images of the ocean surface. A two-layer, shallow-water model is employed using a periodic channel on an f-plane. The model is initialized with a unidirectional upper-Ocean momentum patch; the lower layer is at rest, and there is no initial interface displacement. A tracer is used to simulate the presence of passive ocean surface fields advected by the flow. The model thus simulates a nonlinear geostrophic adjustment process at finite Rossby number with a strong radiated wave field and rapid tracer advection. Several types of tracer configuration result, depending upon the size of the Rossby number and the ratio of the patch size to the internal deformation radius. The values of these parameters determine the degree of symmetry of the mushroom pattern, or whether a mushroom tracer distribution even results from the initial flow field. The numerical model is always operated with the ratio of upper layer to lower layer heights small, and analytical calculations using the reduced-gravity, shallow-water equations are used to interpret the numerical results.