Atmosphere Ocean Science Colloquium

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The latitudinal dependence of geostrophic turbulence in the atmosphere and ocean

Speaker: Rei Chemke, Columbia

Location: Warren Weaver Hall 1302

Date: Wednesday, February 7, 2018, 3:30 p.m.

Synopsis:

The study of atmospheric and oceanic eddies is important for understanding the dynamics of the general circulation in the atmosphere and ocean and the governing scales within. Extant theories for the behavior of these eddies, such as geostrophic turbulence, rely on the theoretical work of two-dimensional turbulence. The latitudinal variations of the mean state (e.g., sphericity, temperature, winds, etc.) adds an additional complexity to geostrophic turbulence theory. Here the behavior of the eddies' energy cycle in both atmosphere and ocean is studied as a function of latitude using both idealized GCM simulations and atmospheric and oceanic reanalysis data. The energy fluxes (i.e., eddy-mean and eddy-eddy interactions) and macroturbulent scales are found to show different behavior poleward and equatorward of a ‘‘supercriticality latitude’’. Poleward of this latitude, where the quasi-geostrophic flow is supercritical to baroclinic instability, a classic geostrophic turbulence picture appears with a barotropization of the flow together with an inverse energy cascade up to the Rhines scale. Equatorward of this latitude the eddy-mean flow interactions play a major role in the balance. The effect of the nonlinear eddy-eddy interactions on the mean flow is further studied by comparing a set of full and quasi-linear idealized simulations. These interactions are found to have a minor effect on the jet scale, which thus coincides with the Rhines scale even when these interactions are absent. The eddy-eddy interactions are not a prerequisite for jet formation in the atmosphere, and even suppress their formation at high latitudes. Under global warming the eddy flow is found be dominated by eddy-mean flow interactions and have a more baroclinic nature.