Regimes of Oceanic Mesoscale Energy Dissipation at Western Boundaries

Abstract Generation of oceanic mesoscale variability serves as the primary energy sink from the general circulation, which motivates efforts to clarify the understanding of the mesoscale energy budget. Some previous studies suggest that western boundaries are key sites of mesoscale energy dissipation, physically rationalized on the basis that both linear Rossby waves and nonlinear eddies transfer energy westward. In contrast, other previous estimates indicate that mesoscale energy is largely dissipated in the vicinity of its generation sites. To reconcile these previous findings, the authors simulate the fate of mesoscale energy propagating toward a western boundary using an idealized isopycnal model. The experimental results are characterized via parameters that quantify the nonlinearity of incident long Rossby waves and reflected short Rossby waves, denoted by and , respectively, based on linear wave theory. For and , the behavior is dominated by linear Rossby waves that experience weak dissipation that is evenly distributed across the domain. For and , the reflected waves become unstable and concentrate energy dissipation near the western boundary. For and , the incident waves become baroclinically unstable in the open ocean and transfer energy downward to be dissipated at the seafloor close to their generation site. These results imply that oceanic western boundaries should only play a key role in dissipating mesoscale energy in regions of weak nonlinearity (within ∼15° of the equator) and imply that the previously assigned importance of western boundaries for mesoscale eddy dissipation may largely be a consequence of eddies being generated nearby.