eprintid: 129528
rev_number: 48
eprint_status: archive
userid: 608
dir: disk0/00/12/95/28
datestamp: 2010-10-24 17:03:38
lastmod: 2021-11-29 00:06:34
status_changed: 2012-11-02 15:07:04
type: article
metadata_visibility: show
item_issues_count: 0
creators_name: Esler, JG
title: The turbulent equilibration of an unstable baroclinic jet
ispublished: pub
divisions: UCL
divisions: B04
divisions: C06
divisions: F59
keywords: 2-LAYER MODEL, BETA-PLANE, MAXIMUM-ENTROPY, FLOWS, ADJUSTMENT, STATES, WAVES, FLUX, INSTABILITY, VORTICES
note: © 2008 Cambridge University Press
abstract: The evolution of an unstable baroclinic jet, subject to a small perturbation, is examined numerically in a quasi-geostrophic two-layer beta-channel model. After a period of initial wave growth, wave breaking leads to turbulence within each layer, and to the eventual equilibration of the flow. The equilibrated flow must satisfy certain dynamical constraints: total momentum is conserved, the total energy is bounded and the flow must be realizable via some area-preserving (diffusive) rearrangement of the initial potential vorticity field in each layer. A theory is introduced that predicts the equilibrated flow in terms of the initial flow parameters. The idea is that the equilibrated state minimizes available potential energy, subject to the constraints on total momentum and total energy, and the further 'kinematic' constraint that the potential vorticity changes through a process of complete homogenization within well-delineated regions in each layer. Within a large region of parameter space, the theory accurately predicts the cross-channel structure and strength of the equilibrated jet, the regions where potential vorticity mixing takes place, and total eddy mass (temperature) fluxes. Results are compared with predictions from a maximum-entropy theory that allows for more general rearrangements of the initial potential vorticity field, subject to the known dynamical constraints. The maximum-entropy theory predicts that significantly more available potential energy is released than is observed in the simulations, and that an unphysical 'exchange' of bands of fluid will occur across the channel in the lower layer. The kinematic constraint of piecewise potential vorticity homogenization is therefore important in limiting the 'efficiency' of release of available potential energy in unstable baroclinic flows. For a typical initial flow, it is demonstrated that if the dynamical constraints alone are considered, then over twice as much potential energy is available for release compared to that actually released in the simulations.
date: 2008-03
publisher: CAMBRIDGE UNIV PRESS
official_url: http://dx.doi.org/10.1017/S0022112008000153
vfaculties: VMPS
oa_status: green
language: eng
primo: open
primo_central: open_green
article_type_text: Article
verified: verified_manual
elements_source: Web of Science
elements_id: 93212
doi: 10.1017/S0022112008000153
language_elements: EN
lyricists_name: Esler, James
lyricists_id: JGESL00
full_text_status: public
publication: J FLUID MECH
volume: 599
pagerange: 241 - 268
issn: 0022-1120
citation:        Esler, JG;      (2008)    The turbulent equilibration of an unstable baroclinic jet.                   J FLUID MECH , 599    241 - 268.    10.1017/S0022112008000153 <https://doi.org/10.1017/S0022112008000153>.       Green open access   
 
document_url: https://discovery-pp.ucl.ac.uk/id/eprint/129528/1/download10.pdf