April 6, 2020: Online Ocean Circulation and Climate Dynamics Colloquium

online via    https://zoom.us/j/589842123

Authors: René Schubert, Franziska U. Schwarzkopf, Burkard Baschek, Jonathan Gula, Richard J. Greatbatch and Arne Biastoch

Abstract:
The comparison of satellite observations with two model simulations and the computation of scale kinetic energy fluxes highlight the importance of including submesoscale effects for a realistic representation of mesoscale Agulhas eddies. In the Agulhas ring path, horizontal-wavenumber spectra of sea-surface height as well as of sea-surface temperature computed from a submesoscale permitting simulation are shown to be in very good agreement with those from the observations. In contrast, a strongly eddying simulation that however does not simulate submesoscale flows shows too less power spectral densities on all scales and too steep spectral slopes. Results of an eddy-detection algorithm applied to the model outputs as well as to a gridded sea-surface height satellite product show that in particular strong cyclones are much better represented when submesoscale flows are permitted in the model. The improvements in the representation of the mesoscale dynamics are attributed to the almost full resolution of the open ocean inverse kinetic energy cascade and a better representation of the formation mechanisms of Agulhas cyclones near the Agulhas Bank. The submesoscale inverse kinetic energy cascade is for the first time attributed to the mesoscale absorption of mixed-layer eddies; the improvements of the cyclone formation to the resolution of submesoscale barotropic instabilities at the northern boundary of the Agulhas Current that contribute to a better representation of the formation of shear-edge eddies and lee cyclones. The comparison of the simulation with submesoscales to the one without shows that the combination of both strengthening effects contributes to an increase of the surface mesoscale kinetic energy in the Cape Basin by 25 %.

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