Abstract
We study the impacts of a continental slope on instability and mesoscale
eddy fluxes in idealized 3-layer numerical model simulations. The
simulations are inspired by and mimic the situation in the Arctic
Ocean’s Beaufort Gyre where anti-cyclonic winds drive anti-cyclonic
currents that are guided by the continental slope. The forcing and
currents are retrograde with respect to topographic Rossby waves. The
focus of the analysis is on eddy potential vorticity (PV) fluxes and
eddy-mean flow interactions under the Transformed Eulerian Mean
framework. Lateral momentum fluxes in the upper layer dominate over the
actual continental slope where eddy form drag, i.e.\
vertical momentum flux, is suppressed due to the topographic PV
gradient. The diagnosis also shows that while eddy momentum fluxes are
up-gradient over parts of the slope, the total quasi-geostrophic PV flux
is down-gradient everywhere. We then calculate the linearly unstable
modes of the time-mean state and find that the most unstable mode
contains several key features of the observed finite-amplitude fluxes
over the slope, including down-gradient PV fluxes. When accounting for
additional unstable modes, all qualitative features of the observed eddy
fluxes in the numerical model are reproduced.