Bifurcation of a coastal current at an escarpment

The evolution of a coastal current as it encounters an escarpment depends s trongly on whether the geometry of the coast and escarpment is right or lef t "handed," independent of the direction of the coastal current. Handedness is defined such that right-handed means that when looking across the escar pment from the deep to the shallow side, the coast is found on the right. T he essential aspects of the difference in behavior of the current in the tw o geometries are captured by a simple quasigeostrophic model of coastal flo w over a step. An exact analytic solution to the nonlinear stationary probl em is obtained. This solution shows that, when a coastal current crosses an escarpment in the left-handed geometry, the speed of the current will incr ease independent of whether the flow is from shallow to deep or from deep t o shallow. For the right-handed geometry, the speed of the current decrease s, also independent of the direction of the coastal flow. In the left (righ t)-handed geometry, there is associated to the coastal flow an inshore (off shore) current along the escarpment. These results are explained in terms o f linear wave theory and vortex dynamics. Numerical simulations are used to examine the evolution of the flow from the initial encounter to the establ ishment of a stationary flow. The relevance of this research is discussed i n light of recent results from laboratory experiments and oceanic observati ons.