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Thursday, August 17, 2006
1:00 PM - 1:30 PM
CNLS Conference Room

Seminar

Geostrophic turbulence - Energy and enstrophy cascades in the atmosphere

Michael Clark
University College Dublin

A full theoretical understanding of the atmospheric energy spectrum remains elusive. Attempts using 2D and 3D and turbulence theory to explain the spectrum have not been wholly satisfactory. Quasi-Geostrophic turbulence exhibits properties of both the 2D and 3D formulations, maintaining energy and enstrophy conservation (like 2D) while allowing vortex stretching (like 3D). We will examine observational evidence and review attempts to explain the spectrum theoretically. In particular, we will note the "kink" in the atmospheric energy spectrum at scales close to 600 km. This kink has been reproduced in some numerical studies but is notably absent in main output of European Centre for Medium-Range Weather Forecasting (ECMWF). The direction of energy flux at small scales in the atmosphere is also disputed and may be dependent on the seasonal and geographic variabilty of convective activity. Our project seeks to study numerically the transition from non-divergent 2D turbulence to Quasi-Geostrophic turbulence. Such a transition requires the incorporation of the effects of the Earth's rotation and allowing for weak compressibility (vortex stretching). The relative importance of these 2 Quasi-Geostrophic effects will be examined and the various fluxes quantified.

Host: Colm Connaughton