Eddies and Friction: Removal of Vorticity from the Wind-Driven Gyre

Baylor Fox-Kemper, Ph.D., 2003
Joseph Pedlosky, Paola Rizzoli, Advisors

Inertia dominates the single-gyre ocean model with small viscosity. Western-intensification doesn't occur with parameters approproaching the ocean's. However, ensuring a mechanism for ultimate removal of vorticity can control the circulation.

I model vorticity removal as a viscosity enhanced very near the solid boundaries parameterizing missing boundary physics. Boundary-enhanced viscosity allows western-intensification even with an inertial layer wider than the frictional region because of the eddy fluxes.

Thereby western-intensified calculations are possible with lower interior viscosity than in previous studies. Interesting behaviors result: a novel boundary-layer, promise for parameterization, gyres rotating opposite the wind, and temporal complexity including basin resonances.

Multiple-gyre calculations have weaker mean circulation than single-gyres with the same parameters. Despite traditional understanding, almost no inter-gyre flux occurs with no-slip boundary conditions. Only with exactly symmetric gyres and slip boundaries is the inter-gyre eddy flux important with small viscosity.

The multiple-gyre circulation is weakened by sinuous instabilities not present in the single-gyre. They efficiently flux vorticity to the boundary and reduce the circulation without an inter-gyre flux, postponing inertial domination to smaller viscosities. In combination with boundary-enhanced viscosity they then control the circulation.