A monopolar vortex encounters a north-south ridge or trough

Results are described from a two-dimensional numerical model in which a cyclonic monopole that moves due to the ß-effect encounters a north-south oriented ridge or trough, the height and depth of which is varied. The fate of the monopole depends on its initial north-south position y₀ (or, equivalently, the value of the constant f₀ in the Coriolis parameter): the monopole can be rebounded, destroyed or trapped by the topography. Only for a narrow range of y₀-positions, depending on the height (depth) of the ridge (trough), can the monopole actually cross the topography, sometimes after being heavily deformed. it is the gradient of the topography-induced vorticity, which deforms the background potential vorticity field due to the ß-effect, that determines the fate of the monopole. This topography-induced vorticity is larger for initial positions more to the north or south, and for higher ridges and deeper troughs.