Vertical Transition in Transport and Mixing in Baroclinic Flows

Numerical simulations in multilevel baroclinic turbulence in a β-plane channel model are discussed, focusing on the transport and mixing behavior. The temperature field in the model is relaxed toward a field consistent with a broad zonal jet with vertical shear that is a Gaussian function of the cro...

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Bibliographic Details
Published in:Journal of the atmospheric sciences 2008-04, Vol.65 (4), p.1137-1157
Main Authors: GREENSLADE, M. D, HAYNES, P. H
Format: Article
Language:English
Subjects:
Atmosphere
Baroclinic flow
Buoyancy
Earth, ocean, space
Equilibrium
Equilibrium flow
Exact sciences and technology
External geophysics
Height
Mathematical models
Meteorology
Numerical simulations
Ocean currents
Physics of the high neutral atmosphere
Potential vorticity
Simulation
Temperature distribution
Temperature fields
Thermal relaxation
Tracers
Transport
Turbulence
Vertical shear
Vortices
Vorticity
Water flow
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Summary:Numerical simulations in multilevel baroclinic turbulence in a β-plane channel model are discussed, focusing on the transport and mixing behavior. The temperature field in the model is relaxed toward a field consistent with a broad zonal jet with vertical shear that is a Gaussian function of the cross-channel coordinate. The resulting statistical equilibrium flow includes an active baroclinic eddy field. The transport and mixing properties are analyzed by considering the fields of potential vorticity and a passive tracer (from which effective diffusivities/equivalent lengths are calculated). The upper part of the flow organizes itself in such a way that there is a transport barrier in the center of the channel, with eddy mixing regions on either side. In the lower part of the flow the eddy mixing occurs across a single broad region, with no central transport barrier. The transition between these two regimes takes place abruptly at a height zT. A large set of simulations is used to map out the variation of zT as a function of external parameters including β, the thermal relaxation rate κT, and the (lower boundary) frictional relaxation rate κM (applied in the lowest model layer only). The transition height zT is argued to be relevant to sharp vertical transitions in transport and mixing observed in atmospheric and oceanic flows.
ISSN:0022-4928
1520-0469
DOI:10.1175/2007JAS2236.1