Instability and mesoscale eddy fluxes in an idealized 3-layer Beaufort Gyre

• Main Authors: Isachsen, Pål Erik, Vogt-Vincent, Noam Sebastian, Johnson, Helen Louise, Nilsson, Johan
• Format: Other/Unknown Material
• Language: unknown
• Published: Authorea, Inc. 2023
• Subjects: Arctic
• Online Access: http://dx.doi.org/10.22541/essoar.170196614.44600790/v1

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.