Constraints on droplet growth in radiatively cooled stratocumulus clouds

P. H. Austin, S. Siems, Y. Wang

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Abstract

Radiative cooling near the top of a layer cloud plays a dominant role in droplet condensation growth. The impact of this cooling on the evolution of small droplets and the formation of precipitation-sized drops is calculated using a microphysical model that includes radiatively driven condensation and coalescence. The cloud top radiative environment used for these calculations is determined using a mixed-layer model of a marine stratocumulus cloud with a subsiding, radiatively cooled inversion. Calculations of the radiatively driven equilibrium supersaturation show that net long wave emission by cloud droplets produces supersaturations below 0.04% for typical nocturnal conditions. While supersaturations as low as this will force evaporation for the droplets smaller than approx= 5 mum, radiatively enhanced growth for larger droplets can reduce the time required to produce precipitation-sized particles by a factor of 2-4, compared with droplets in a quiescent cloud without flux divergence. (from Authors)

Original languageEnglish
JournalJournal of Geophysical Research
Volume100
Issue numberD7
Publication statusPublished - 1 Jan 1995
Externally publishedYes

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