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Effects of Diffusion on Baroclinic Instability of the Zonal Wind

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  • 1 Institute of Advanced Studies, Australian National University, Canberra
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Abstract

The baroclinic instability problem is reformulated to include diffusion of both heat and momentum through conduction and viscosity. A priori arguments suggest that the effects of heat conduction should dominate those of viscosity in the critical layer, where local wind speed equals wave speed and the adiabatic model for small disturbances is not uniformly valid. An asymptotic solution of the singular perturbation problem (based on the hypothesis that the Peclet and Reynolds numbers tend to infinity) supports this conjecture but also implies that the effects of diffusion on baroclinic instability are negligible insofar as the critical layer is within the geostrophic regime of the mean flow. This last condition is satisfied for the disturbances of principal meteorological interest.

Abstract

The baroclinic instability problem is reformulated to include diffusion of both heat and momentum through conduction and viscosity. A priori arguments suggest that the effects of heat conduction should dominate those of viscosity in the critical layer, where local wind speed equals wave speed and the adiabatic model for small disturbances is not uniformly valid. An asymptotic solution of the singular perturbation problem (based on the hypothesis that the Peclet and Reynolds numbers tend to infinity) supports this conjecture but also implies that the effects of diffusion on baroclinic instability are negligible insofar as the critical layer is within the geostrophic regime of the mean flow. This last condition is satisfied for the disturbances of principal meteorological interest.

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