Influences of Mesoscale Ocean Eddies on Flow Vertical Structure in a
Resolution-Based Model Hierarchy
Abstract
The understanding and representation of energetic transfers associated
with ocean mesoscale eddies is fundamental to the development of
parameterizations for climate models. We investigate the influence of
eddies on flow vertical structure as a function of underlying dynamical
regime and grid resolution. We employ the GFDL-MOM6 in an idealized
configuration and systematically consider four horizontal resolutions:
1/4, 1/8, 1/16, and 1/32 degree. We analyze the distributions of
potential and kinetic energy, decomposed into barotropic and baroclinic,
and eddy and mean parts. Kinetic energy increases and potential energy
decreases as resolution increases and captures more
baroclinically-unstable modes. The dominant trend in vertical structure
is an increasing fraction of kinetic energy going into the barotropic
mode, particularly its eddy component, as eddies are increasingly
resolved. We attribute the increased baroclinicity at low resolutions to
inaccurate representation of vertical energy fluxes, leading to
suppressed barotropization and energy trapping in high vertical modes.
We also explore how the underlying dynamical regime influences energetic
pathways. In cases where large-scale flow is dominantly barotropic,
resolving the deformation radius is less crucial to accurately capturing
the flow’s vertical structure. We find the barotropic kinetic energy
fraction to be a useful metric in assessing vertical structure. In the
highest-resolution case, the barotropic kinetic energy fraction
correlates with the scale separation between the deformation scale and
the energy-containing scale, i.e. the extent of the eddy-driven inverse
cascade. This work suggests that mesoscale eddy parameterizations should
incorporate the energetic effects of eddies on vertical structure in a
scale-aware, physically-informed manner.