John Marshall

Cecil and Ida Green Professor of Oceanography, MIT

Transformed Eulerian-mean theory. part II: Potential vorticity homogenization and the equilibrium of a wind- and buoyancy-driven zonal flow

Transformed Eulerian-mean theory. part II: Potential vorticity homogenization and the equilibrium of a wind- and buoyancy-driven zonal flow.

(Kuo, A and Plumb, RA and Marshall, J), JOURNAL OF PHYSICAL OCEANOGRAPHY, vol. 35, no. 2, pp. pages, 2005.

Abstract

The equilibrium of a modeled wind- and buoyancy-driven, baroclinically unstable, flow is analyzed using the transformed Eulerian-mean (TEM) approach described in Part I. Within the near-adiabatic interior of the flow, Ertel potential vorticity is homogenized along mean isopycnals- a finding readily explained using TEM theory, given the geometry of the domain. The equilibrium, zonal-mean buoyancy structure at the surface is determined entirely by a balance between imposed surface fluxes and residual mean and eddy buoyancy transport within a “surface diabatic layer”. Balance between these same processes and the wind stress determines the stratification, and hence potential vorticity, immediately below this layer. Ertel potential vorticity homogenization below then determines the mean buoyancy structure everywhere. Accordingly, the equilibrium structure of this flow can be described-and quantitatively reproduced-from knowledge of the eddy mixing rates within the surface diabatic zone and the depth of this zone, together with potential vorticity homogenization beneath. These results emphasize the need to include near-surface buoyancy transport, as well as interior PV transport, in eddy parameterization schemes. They also imply that. In more realistic models, the surface buoyancy balances may be impacted by processes in remote locations that allow diapycnal flow.

doi = 10.1175/JPO-2670.1