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On near resonances and symmetry breaking in forced rotating flows at moderate Rossby number

Published online by Cambridge University Press:  05 July 2005

LESLIE M. SMITH
Affiliation:
Departments of Mathematics and Engineering Physics, University of Wisconsin, Madison, WI 53706, USA
YOUNGSUK LEE
Affiliation:
Department of Mathematics, Simon Fraser University, Burnaby, BC V5A 1S6, Canada

Abstract

Numerical simulations are used to study a series of reduced models of homogeneous, rotating flow at moderate Rossby numbers $Ro \,{\approx}\, 0.1$, for which both numerical and physical experiments show the generation of quasi-two-dimensional vortices and symmetry breaking in favour of cyclones. A random force at intermediate scales injects energy at a constant average rate. The nonlinear term of reduced models is restricted to include only a subset of triad interactions in Fourier space. Reduced models of near-resonant, non-resonant and near two-dimensional triad interactions are considered. Only the model of near resonances reproduces all of the important characteristics of the full simulations: (i) efficient energy transfer from three-dimensional forced modes to two-dimensional large-scale modes, (ii) large-scale energy spectra scaling approximately as $k_h^{-3}$, where $k_h$ is the wavenumber in the plane perpendicular to the axis of rotation, and (iii) strong cyclone/anticyclone asymmetry in favour of cyclones. Non-resonances, defined as the complement to near resonances, act to reduce the energy transfer to large scales.

Type
Papers
Copyright
© 2005 Cambridge University Press

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