Submesocale Secondary Instabilities and their Significance for
the Upper Ocean Dynamics

Xavier Capet and James McWilliams
University of California at Los Angeles

The existence of a sub-mesoscale instability of mesoscale eddies as a necessary route to dissipation for the oceanic general circulation has been anticipated by theory and several instances have been demonstrated in highly idealized settings, but their role in more realistic oceanic situations is far from clear. We are investigating this phenomenon in an eastern boundary upwelling system configuration. Solutions for an identical 720km x 720km domain are computed at 12, 6, 3, 1.5, and 0.75 km horizontal grid resolutions for 1 year during a statistical equilibrium phase. The resulting upper-ocean kinetic energy spectra exhibit a shallowing when going from 12 to 1.5 km resolution, which is the signature of an increasingly efficient forward cascade of energy to dissipation; accompanying flow visualization implicates an increasing degree of sub-mesoscale instability. There seems to be a spectrum saturation beyond 1.5 km, suggesting convergence of the sub-mesoscale simulation. As for their upscale implications, the sub-mesoscale processes are associated with an important vertical heat redistribution in the mixed layer, significantly contributing to restratification there. We observe a much weaker submesocale activity in the ocean interior but implications for the large scale dynamics are not ruled out.