Deterministic Model of the Eddy Dynamics for a Midlatitude Ocean Model

Mesoscale eddies, although being on scales of O(20-100) km, have a disproportionate role in shaping the mean stratification, which varies on the scale of O(1000) km. With the increase in computational power, we are now able to partially resolve the eddies in basin-scale and global ocean simulations, a model resolution often referred to as mesoscale permitting. It is well known, however, that due to gridscale numerical viscosity, mesoscale-permitting simulations have less energetic eddies and consequently weaker eddy feedback onto the mean flow. In this study, we run a quasigeostrophic model at mesoscale-resolving resolution in a double gyre configuration and formulate a deterministic closure for the eddy rectification term of potential vorticity (PV), namely, the eddy PV flux divergence. Our closure successfully reproduces the spatial patterns and magnitude of eddy kinetic and potential energy diagnosed from the mesoscale-resolving model. One novel point about our approach is that we account for nonlocal eddy feedbacks onto the mean flow by solving the subgrid eddy PV equation prognostically in addition to the mean PV.

Automated summary

Mesoscale eddies play an important role in shaping the mean stratification, but their feedback onto the mean flow is weaker in mesoscale-permitting simulations. In this study, a deterministic closure is formulated to reproduce the spatial patterns and magnitude of eddy kinetic and potential energy. Nonlocal eddy feedbacks onto the mean flow are also considered by solving the subgrid eddy potential vorticity equation.