The influence of topography on mesoscale eddy mass transport

The mass transport capacity of mesoscale eddies over their long-period evolution is investigated by a series of passive tracer simulations within a numerical model. The eddy nonlinearity causes fluid parcels to be trapped within the closed potential vorticity contours, which then migrate with the eddy. The mass transport capacity of a mesoscale eddy decayed during the spontaneous generation of near-inertial waves (NIWs) and its interaction with seafloor topography. During the spontaneous NIW generation, the mass transport capacity declines due to the reduction in eddy rotational speed. The interaction between a mesoscale eddy and topography involves multiple mechanisms, resulting in a substantial decrease in the eddy radius and consequently impeding its mass transport capacity. When a mesoscale eddy encounters the topography, lee waves and submesoscale filaments are generated, and the eddy radius decreases, modulating the relative vorticity to balance the ambient vorticity variations induced by the topography. The greater the topography gradient, the more rapidly the mass transport of a mesoscale eddy decays. The leakage of mass transported by a cyclonic eddy due to the interaction between the eddy and topography is greater than that in the interaction between an anticyclonic eddy and topography. The average relative mass transport rates for both anticyclonic and cyclonic mesoscale eddies exhibit linear relationships with the topography within the range of 500–1000 m. When mesoscale eddies interact with the topography above 1100 m, baroclinic instability occurs, causing a significant fraction of the trapped fluid parcels to escape from the eddies.