Shear Zone Asymmetry in the Observed and Simulated Quasi-Biennial Oscillations

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  • 1 Department of Atmospheric Sciences, University of Washington, Seattle 98195
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Abstract

Reasons underlying the asymmetry in shear-zone intensity in the observed and simulated quasi-biennial oscillations are investigated. It is shown that much of the incorrect model asymmetry originates in the differing equipartition laws of the Kelvin and Rossby gravity waves. The observed asymmetry cannot entirely be explained by vertical advection due to the residual mean meridional circulation. It is suggested that latitudinal shear plays a role in the observed shear zone asymmetry by reducing the degree of inflection in the dependence of Rossby-gravity wave vertical group velocity on intrinsic frequency via a curvature-induced change in the effective planetary vorticity gradient. The experiments are suggestive of a possible mechanical dissipation of the Rossby-gravity wave.

Abstract

Reasons underlying the asymmetry in shear-zone intensity in the observed and simulated quasi-biennial oscillations are investigated. It is shown that much of the incorrect model asymmetry originates in the differing equipartition laws of the Kelvin and Rossby gravity waves. The observed asymmetry cannot entirely be explained by vertical advection due to the residual mean meridional circulation. It is suggested that latitudinal shear plays a role in the observed shear zone asymmetry by reducing the degree of inflection in the dependence of Rossby-gravity wave vertical group velocity on intrinsic frequency via a curvature-induced change in the effective planetary vorticity gradient. The experiments are suggestive of a possible mechanical dissipation of the Rossby-gravity wave.

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