Parameterization of Horizontal Transport of Vorticity by Cumulus Convection

Han-Ru Cho Department of Physics, University of Toronto, Ontario, Canada M5S IA7

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Lawrence Cheng Department of Physics, University of Toronto, Ontario, Canada M5S IA7

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Abstract

Dynamic processes of cumulus clouds which may produce significant horizontal eddy transport of vertical vorticity in the tropical atmosphere are discussed. It is shown in this paper that horizontal eddy transport of vorticity by cumulus convection, if it exists, must be due entirely to the irrotational component of the horizontal wind produced by clouds. The ability of clouds to produce this eddy transport depends critically on the presence of cyclonic-anticyclonic vortex couplets in the cloud circulations. The generation processes of these vortex couplets are also discussed.

A formula is derived to parameterize this eddy transport process in the large-scale mean vorticity equation. The formulation is tested using. GATE data. GATE-A/B-scale mean vorticity budgets are analyzed for two 1-day periods during Phase III of the experiment. The agreements between the theoretically predicted and the observed apparent vorticity sources are found to be much improved by including the effects of cloud horizontal eddy transport of vertical vorticity.

Abstract

Dynamic processes of cumulus clouds which may produce significant horizontal eddy transport of vertical vorticity in the tropical atmosphere are discussed. It is shown in this paper that horizontal eddy transport of vorticity by cumulus convection, if it exists, must be due entirely to the irrotational component of the horizontal wind produced by clouds. The ability of clouds to produce this eddy transport depends critically on the presence of cyclonic-anticyclonic vortex couplets in the cloud circulations. The generation processes of these vortex couplets are also discussed.

A formula is derived to parameterize this eddy transport process in the large-scale mean vorticity equation. The formulation is tested using. GATE data. GATE-A/B-scale mean vorticity budgets are analyzed for two 1-day periods during Phase III of the experiment. The agreements between the theoretically predicted and the observed apparent vorticity sources are found to be much improved by including the effects of cloud horizontal eddy transport of vertical vorticity.

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