Interaction of a monopolar vortex with a topographic ridge

The interaction of a monopolar vortex with a cosine-shaped topographic ridg e at the equator is investigated with a two-dimensional numerical model, wh ere the (cyclonic) monopole has a self-induced northwest-ward motion due to the beta-effect. The Fate of the monopole depends on the width and height of the ridge, but, more importantly, on the orientation of the ridge. Where as monopoles are always seen to cross an east-west or northeast-southwest r idge, a north-south ridge can cause such deformations in the monopole's sha pe that it either splits into two parts (where the associated secondary vor tex may or may not also cross the ridge) or it is destroyed. The computatio ns show that the monopole can only cross the top of the ridge once it has g athered sufficient positive potential vorticity at its (north)west side. Th e vortex achieves this by moving along the ascending side of the ridge, wes tward for the east-west ridge and northward for the north-south ridge, befo re crossing the summit.