Advancing eddy parameterizations: Dynamic energy backscatter and the
role of subgrid advection and stochastic forcing
Abstract
A universal approach to overcome resolution limitations in the ocean is
to parametrize physical processes. The traditional method of
parametrizing mesoscale range processes on eddy-permitting mesh
resolutions, known as a viscous momentum closure, tends to
over-dissipate eddy kinetic energy. To return excessively dissipated
energy to the system, the viscous closure is equipped with a dynamic
energy backscatter, which amplitude is based on the amount of unresolved
kinetic energy (UKE). Our study suggests including the advection of UKE
to consider the effects of nonlocality on the subgrid. Furthermore, we
suggest incorporating a stochastic element into the subgrid energy
equation to account for variability, which is not present in a fully
deterministic approach. This study demonstrates increased eddy activity
and highlights improved flow characteristics. In addition, we provide
diagnostics of optimal scale separation between dissipation and
injection operators. The implementations are tested on two intermediate
complexity setups of the global ocean model FESOM2: an idealized channel
setup and a double-gyre setup.