UNSTEADY ABYSSAL CIRCULATION DRIVEN BY A DISCRETE BUOYANCY SOURCE IN A CONTINUOUSLY STRATIFIED OCEAN

Analytical and numerical models are presented for linear quasigeostrop hic buoyancy-driven flow forced by a time periodic pulsating point mas s source in a continuously stratified, incompressible beta-plane ocean with constant Brunt-Vaisala frequency. The source represents the seas onal introduction of dense water into the abyssal ocean and is located oil a linear sloping bottom of arbitrary orientation. The ocean domai n is horizontally unbounded and of infinite depth. Rayleigh friction i s incorporated into the horizontal momentum equations and appears at o rder Rossby number in the quasigeostrophic expansions. In the density equation the influence of Rayleigh friction and Laplacian friction are each considered in turn Analytical solutions are obtained in the case of 1) a midlatitude beta plane with no bottom slope and 2) an f plane with a bottom slope. In both of these problems the fluid is initially at rest and the mass source is switched on and maintained. A three-di mensional radiating field of baroclinic Rossby waves is generated, whi ch are bottom trapped in the second problem. If the time between succe ssive mass pulses is sufficiently long to enable the free waves to dom inate the solution, it is found that the azimuthal wavelength of the b ottom-trapped vorticity wave decreases thereby producing a series of e longated vortices. The present generation of ocean general circulation models would be unable to resolve this bottom-trapped flow. Numerical solutions are presented for the case of a sloping bottom of arbitrary orientation on a beta plane when the time periodic source exists for all time. During each cycle of the forcing a bottom-trapped anticyclon ic vortex is generated at the source and propagates in a direction dic tated by the relative role of the planetary and topographic beta effec ts. The horizontal distance that the vortex propagates before decaying is larger when Laplacian mixing is incorporated in the density equati on rather than Rayleigh damping. A study of how slope magnitude and or ientation influences the solution is presented.