Rapid Development of High Ice Particle Concentrations in Small Polar Maritime Cumuliform Clouds

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  • 1 Atmospheric Sciences Department, University of Washington, Seattle, Washington
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Abstract

Extremely high ice particle concentrations developed rapidly in the ascending tops of maritime cumulus congestus clouds after drizzle drops had already formed below this level by the collision–coalescence mechanism. In one building cloud with a top temperature no colder than −8°C, the ice particle concentrations increased from 0 to >350 L−1 within 9 min. In another cloud with a top temperature no colder than −13°C, the ice particle concentrations increased from ≤1 to ∼1100 L−1 within 12 min. Subsequently, the ice particle concentrations in these clouds decreased, even though the cloud top temperature of one of the clouds continued to decrease to −23.5°C.

The mechanism responsible for these prodigious increases in ice particle concentrations is not clear. The concentrations built too fast to be explained by the riming-splintering mechanism as it is presently formulated. It is suggested that high ice particle concentrations might form in localized pockets of high supersaturation with respect to water.

Abstract

Extremely high ice particle concentrations developed rapidly in the ascending tops of maritime cumulus congestus clouds after drizzle drops had already formed below this level by the collision–coalescence mechanism. In one building cloud with a top temperature no colder than −8°C, the ice particle concentrations increased from 0 to >350 L−1 within 9 min. In another cloud with a top temperature no colder than −13°C, the ice particle concentrations increased from ≤1 to ∼1100 L−1 within 12 min. Subsequently, the ice particle concentrations in these clouds decreased, even though the cloud top temperature of one of the clouds continued to decrease to −23.5°C.

The mechanism responsible for these prodigious increases in ice particle concentrations is not clear. The concentrations built too fast to be explained by the riming-splintering mechanism as it is presently formulated. It is suggested that high ice particle concentrations might form in localized pockets of high supersaturation with respect to water.

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