Dissipation of mesoscale eddies at a western boundary via a direct energy cascade

The fate of mesoscale eddy kinetic energy represents a large source of uncertainty in the global ocean energy budget. Satellite altimetry suggests that mesoscale eddies vanish at ocean western boundaries. However, the fate of the eddies' kinetic energy remains poorly known. Here we show that the generation of small-scale turbulence as eddy flow impinges on the steep and corrugated slope of an ocean western boundary plays a dominant role in the regional decay of mesoscale eddy kinetic energy. We compare altimetry-based estimates of mesoscale eddy kinetic energy decline with measurements of turbulent dissipation. Mesoscale eddies are found to decay at a rate of 0.016 +/- 0.012 GW and 0.023 +/- 0.017 GW for anticyclonic and cyclonic eddies, respectively, similar to the observed turbulent dissipation rate of 0.020 +/- 0.011 GW. This demonstrates that a major direct transfer of mesoscale eddy kinetic energy to small, dissipative scales can be effectively triggered by the eddies' interaction with the western boundary topography.

Automated summary

This study finds that small-scale turbulence generated when eddy flow impacts the steep and corrugated slope of an ocean western boundary plays a dominant role in the regional decay of mesoscale eddy kinetic energy. Comparison with measurements of turbulent dissipation shows that the decay rate of mesoscale eddies is similar to the observed turbulent dissipation rate. This demonstrates the effective transfer of mesoscale eddy kinetic energy to small, dissipative scales triggered by the eddies' interaction with the western boundary topography.