Interaction of a counter-rotating vortex pair with a vortex over bathymetry

We consider the interaction of an anticyclonic vortex (an anticyclone) lying above a basin (a depression in the bathymetry) and an incoming pair of opposite-signed vortices in a two-layer quasi-geostrophic flow. We show that the anticyclone lying above the basin may merge with the anticyclone of the incoming pair. We show that the size of the parameter space where merger occurs is large, indicating that such an interaction may easily occur. This helps explain why such mergers have been observed over oceanic basins such as the Lofoten basin.