Vertical structure and energetic constraints for a backscatter
parameterization of ocean mesoscale eddies
Abstract
Mesoscale eddies modulate the stratification, mixing and dissipation
pathways, and tracer transport of oceanic flows over a wide range of
spatiotemporal scales. The parameterization of buoyancy and momentum
fluxes associated with mesoscale eddies thus presents an evolving
challenge for ocean modelers, particularly as modern climate models
approach eddy-permitting resolutions. Here we present a parameterization
targeting such resolutions through the use of a subgrid mesoscale eddy
kinetic energy budget (MEKE) framework. Our study presents two novel
insights: (1) both the potential and kinetic energy effects of eddies
may be parameterized via a kinetic energy backscatter, with no
Gent-McWilliams along-isopycnal transport; (2) a dominant factor in
ensuring a physically-accurate backscatter is the vertical structure of
the parameterized momentum fluxes. We present simulations of
1/2$^\circ$ and 1/4$^\circ$
resolution idealized models with backscatter applied to the equivalent
barotropic mode. Remarkably, the global kinetic and potential energies,
isopycnal structure, and vertical energy partitioning show significantly
improved agreement with a 1/32$^\circ$ reference
solution. Our work provides guidance on how to parameterize mesoscale
eddy effects in the challenging eddy-permitting regime.