Modelling outflows, coastal currents and eddies
Several types of flows driven by outflows on the continental shelf are examined mathematically and numerically. Within a quasigeostrophic framework, a variety of vertical structures and topographies are used. Features are explained in terms of potential vorticity conservation. The combined effects of topography and anomalous vorticity of the outflow are studied. First, shelf-like topography is considered. The role of topographic wave radiation is studied using the linearised barotropic potential vorticity equation for a weak outflow with zero vorticity. Contour dynamics is used for stronger outflows with relative vorticity. Next, the effects of anomalous vorticity in driving such coastal currents are studied using 11/2-layer model and its interaction with topography. Simulations show that the strong tendency for the development of anticyclonic eddy near topographic change. Two-layer outflows and their interaction with topography are examined. Purely buoyancy driven outflows are considered in which only one of two layers enters the flow domain. Purely barotropic outflows are also considered. Simulations show the development of eddies by interaction with topography in the lower fluid. The effect of topography whose gradient lies perpendicular to the coastline on coastal currents and eddies is investigated. The formation of dipole eddies is found to be a robust feature when the coastal current interacts with the topography depending on the sign of the topographic gradient. The stability of a two-layer converging/diverging coastal jet associated with piecewise constant potential vorticity is studied numerically. Baroclinic instability is demonstrated. The origin of the instability appears first at the coast, and may explain the meandering and eddying associated with detaching western boundary currents. The final study revisits the barotropic outflow problem. Owing to boundary layer separation at the exit, the outflow may consist of a dipolar structure. The interaction of this dipole with shelf-like topography is studied numerically.