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- Author or Editor: Vitaly D. Larichev x
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Abstract
A horizontally homogeneous two-layer quasigeostrophic model with imposed environmental vertical shear is used to study eddy energies and fluxes in the regime in which an inverse barotropic energy cascade excites eddies of much larger scale than the deformation radius. It is shown that the eddy potential vorticity flux, “thickness” flux, and the extraction of energy from the background flow are dominated by the largest eddies excited by the cascade, and not by deformation-scale eddies. The role of the latter is a catalytic one of transferring the baroclinic energy cascading downscale into the barotropic mode, thereby energizing the inverse cascade.
Based on this picture, scaling arguments are developed for the eddy energy level and potential vorticity flux in statistical equilibrium. The potential vorticity flux can be thought of as generated by a diffusivity of magnitude Ukd/k2 0 , where U is the difference between the mean currents in the two layers, kd is the inverse of the deformation radius, and k 0 is the wavenumber of the energy-containing eddies. This result is closely related to that proposed by Green, although the underlying dynamical picture is different.
Abstract
A horizontally homogeneous two-layer quasigeostrophic model with imposed environmental vertical shear is used to study eddy energies and fluxes in the regime in which an inverse barotropic energy cascade excites eddies of much larger scale than the deformation radius. It is shown that the eddy potential vorticity flux, “thickness” flux, and the extraction of energy from the background flow are dominated by the largest eddies excited by the cascade, and not by deformation-scale eddies. The role of the latter is a catalytic one of transferring the baroclinic energy cascading downscale into the barotropic mode, thereby energizing the inverse cascade.
Based on this picture, scaling arguments are developed for the eddy energy level and potential vorticity flux in statistical equilibrium. The potential vorticity flux can be thought of as generated by a diffusivity of magnitude Ukd/k2 0 , where U is the difference between the mean currents in the two layers, kd is the inverse of the deformation radius, and k 0 is the wavenumber of the energy-containing eddies. This result is closely related to that proposed by Green, although the underlying dynamical picture is different.
Abstract
This paper considers the requirements that must be satisfied in order to provide a stable and physically based isoneutral tracer diffusion scheme in a z-coordinate ocean model. Two properties are emphasized: 1) downgradient orientation of the diffusive fluxes along the neutral directions and 2) zero isoneutral diffusive flux of locally referenced potential density. It is shown that the Cox diffusion scheme does not respect either of these properties, which provides an explanation for the necessity to add a nontrivial background horizontal diffusion to that scheme. A new isoneutral diffusion scheme is proposed that aims to satisfy the stated properties and is found to require no horizontal background diffusion.
Abstract
This paper considers the requirements that must be satisfied in order to provide a stable and physically based isoneutral tracer diffusion scheme in a z-coordinate ocean model. Two properties are emphasized: 1) downgradient orientation of the diffusive fluxes along the neutral directions and 2) zero isoneutral diffusive flux of locally referenced potential density. It is shown that the Cox diffusion scheme does not respect either of these properties, which provides an explanation for the necessity to add a nontrivial background horizontal diffusion to that scheme. A new isoneutral diffusion scheme is proposed that aims to satisfy the stated properties and is found to require no horizontal background diffusion.
