Joint Seminar: The latitudinal dependence of geostrophic turbulence in the atmosphere and ocean

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.

Datum

05.04.2017

Uhrzeit

13:30 Uhr

Ort

Bundesstr. 53, room 022/023
Seminar Room 022/023, Ground Floor, Bundesstrasse 53, 20146 Hamburg, Hamburg

ReferentIn

Rei Chemke, Department of Applied Physics and Applied Mathematics Columbia University

Chair

Marco Giorgetta

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