Wave-Induced Instabilities in an Atmosphere Near Saturation

F. Einaudi Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder 80302

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D. P. Lalas Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder 80302

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Abstract

In this paper the stability and the propagation characteristics of internal gravity waves that propagate in an atmosphere near saturation and, over some height range, create the appropriate thermodynamic conditions for condensation to occur for a fraction of the wave cycle, are investigated. It is shown that if the atmosphere, over some height range, is close enough to saturation, a linear stability analysis is possible and results in a modified Richardson criterion, based on a new Brunt-Väisälä frequency nav smaller than the corresponding nu with condensation effects neglected. Since nav2 can become negative, even though the atmosphere is originally statically stable, the ability of gravity waves to trigger convective processes in a moist atmosphere is demonstrated. Finally, a numerical example is presented to illustrate the alterations of the characteristics of propagation.

Abstract

In this paper the stability and the propagation characteristics of internal gravity waves that propagate in an atmosphere near saturation and, over some height range, create the appropriate thermodynamic conditions for condensation to occur for a fraction of the wave cycle, are investigated. It is shown that if the atmosphere, over some height range, is close enough to saturation, a linear stability analysis is possible and results in a modified Richardson criterion, based on a new Brunt-Väisälä frequency nav smaller than the corresponding nu with condensation effects neglected. Since nav2 can become negative, even though the atmosphere is originally statically stable, the ability of gravity waves to trigger convective processes in a moist atmosphere is demonstrated. Finally, a numerical example is presented to illustrate the alterations of the characteristics of propagation.

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