Eddy-Current Interactions using a Two-Layer Quasi-Geostrophic Model

Abstract

Abstract Processes associated with interactions between a mesoscale eddy and an ocean current are examined using a two-layer quasi-geostrophic model. Model configuration is chosen so that the eddy tends to approach the current, and the chance for interactions is enhanced. The upper-layer current flows with a coast to the right (looking downstream) over a bottom slope that deepens downstream. The eddy, initially placed offshore of the current, approaches the current, as qualitatively explained by a topographic Rossby wave, and interacts with the current. The cyclonic (anticyclonic) eddy exhibits an upslope (downslope) movement due to nonlinearlity. This model configuration resembles the Norwegian Coastal Current and the East Greenland Current over the downstream sides of the sills. Once the eddy influences the current, meanders are developed in the baroclinically and barotropically unstable current. The cyclonic eddy travels upstream and interacts intensely with an anticyclonic potential vorticity anomaly associated with the seaward meander upstream of the eddy. Hence, the eddy is pulled further toward the current. This result is contrary to the prediction based on the assumption that the eddy travels downstream nearly at a meander phase speed. The cyclonic eddy keeps its identity nearby the current, and it crosses the current in some cases. The anticyclonic eddy travels nearly at the meander phase-speed and becomes part of a seaward meander. Its upper-layer structure can be lost through the interactions with the current, and a new anticyclonic eddy is regenerated from the large -amplitude meander. The anticyclonic eddy excites meanders with wavelengths nearly identical to a wavelength of the fastest growing mode predicted by linear theory. The cyclonic eddy travels upstream and induces longer wavelength meanders, which have smaller phase speeds.