A Numerical Experiment in Dry and Moist Convection Including the Rain Stage

Geirmundur Árnason The Travelers Research Center, Inc., Hartford, Conn.

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Richard S. Greenfield The Travelers Research Center, Inc., Hartford, Conn.

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Edward A. Newburg The Travelers Research Center, Inc., Hartford, Conn.

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Abstract

Dry and moist convective slab-symmetric cells, initiated by means of a buoyant bubble, have been studied by solving numerically the appropriate physical equations. In the case of moist convection, by including the bulk effects of the microphysics of cloud and precipitation, a precipitating roll cloud was simulated.

The pressure distribution accompanying the convection was obtained by solving a partial differential equation (the balance equation). The dynamic pressure is much different from the hydrostatic pressure.

Forces governing the vertical motion have been studied in some detail. The pressure force is shown to initiate and maintain inflow and outflow in the convective cell and to create forced descent outside the rising bubble as required by mass continuity. It also opposes the upward motion of the bubble and gives rise to a drag similar to the form drag of a body moving through a viscous fluid.

A “hot tower” develops near the top of the cloud while negative buoyancy develops in its lower half; had the experiment been continued, this would have led to a downdraft.

Abstract

Dry and moist convective slab-symmetric cells, initiated by means of a buoyant bubble, have been studied by solving numerically the appropriate physical equations. In the case of moist convection, by including the bulk effects of the microphysics of cloud and precipitation, a precipitating roll cloud was simulated.

The pressure distribution accompanying the convection was obtained by solving a partial differential equation (the balance equation). The dynamic pressure is much different from the hydrostatic pressure.

Forces governing the vertical motion have been studied in some detail. The pressure force is shown to initiate and maintain inflow and outflow in the convective cell and to create forced descent outside the rising bubble as required by mass continuity. It also opposes the upward motion of the bubble and gives rise to a drag similar to the form drag of a body moving through a viscous fluid.

A “hot tower” develops near the top of the cloud while negative buoyancy develops in its lower half; had the experiment been continued, this would have led to a downdraft.

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