MODELS OF PRECIPITATING CUMULUS TOWERS

JOANNE SIMPSON Atmospheric Physics and Chemistry Laboratory, ESSA, Miami, Fla.

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VICTOR WIGGERT Atmospheric Physics and Chemistry Laboratory, ESSA, Miami, Fla.

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Abstract

This paper presents a model of the growth of cumulus clouds. The water content and maximum height of rising towers are calculated using a buoyancy equation with consideration of effects of entrainment and water load. The latter is subject to effects of modeled microphysical effects. Precipitation growth is parameterized in terms of an autoconversion equation and a collection equation. A precipitation fallout scheme is devised that depends on water content, drop spectrum, and the vertical rise rate of the tower.

Then “freezing subroutines” are devised to model the effects of silver-iodide seeding. A hierarchy of seeding routines, using different ice collection efficiencies and terminal velocities, is partially tested against the data of the Stormfury 1965 tropical cumulus-seeding experiment.

Some preliminary numerical experiments on warm clouds are performed, assuming changes in drop spectra from hygroscopic seeding.

Abstract

This paper presents a model of the growth of cumulus clouds. The water content and maximum height of rising towers are calculated using a buoyancy equation with consideration of effects of entrainment and water load. The latter is subject to effects of modeled microphysical effects. Precipitation growth is parameterized in terms of an autoconversion equation and a collection equation. A precipitation fallout scheme is devised that depends on water content, drop spectrum, and the vertical rise rate of the tower.

Then “freezing subroutines” are devised to model the effects of silver-iodide seeding. A hierarchy of seeding routines, using different ice collection efficiencies and terminal velocities, is partially tested against the data of the Stormfury 1965 tropical cumulus-seeding experiment.

Some preliminary numerical experiments on warm clouds are performed, assuming changes in drop spectra from hygroscopic seeding.

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