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Constraints on droplet growth in radiatively cooled stratocumulus clouds Austin, Philip H.; Siems, Steven T.; Wang, Yinong
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 droplets smaller than ≈ 5 μm, 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. The impact of this radiative enhancement on the acceleration of coalescence is equivalent to that produced in updrafts of 0.1–0.5 ms−1, and varies linearly with the total emitted flux (the “radiative exchange”). An edited version of this paper was published by AGU. Copyright 1995 American Geophysical Union.
Item Metadata
| Title |
Constraints on droplet growth in radiatively cooled stratocumulus clouds
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| Creator | |
| Publisher |
American Geophysical Union
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| Date Issued |
1995-04-05
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| Description |
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 droplets smaller than ≈ 5 μm, 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. The impact of this radiative enhancement on the acceleration of coalescence is equivalent to that produced in updrafts of 0.1–0.5 ms−1, and varies linearly with the total emitted flux (the “radiative exchange”). An edited version of this paper was published by AGU. Copyright 1995 American Geophysical Union.
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| Genre | |
| Type | |
| Language |
eng
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| Date Available |
2016-11-07
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| Provider |
Vancouver : University of British Columbia Library
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| Rights |
Attribution-NonCommercial-NoDerivatives 4.0 International
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| DOI |
10.14288/1.0041771
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| URI | |
| Affiliation | |
| Citation |
Austin, Philip H., Siems, Steven T., Wang , Y. 1995. Constraints on droplet growth in radiatively cooled stratocumulus clouds, Journal of Geophysical Research Atmospheres, 100 (D7) 14231–14242.
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| Publisher DOI |
10.1029/95JD01268.
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| Peer Review Status |
Reviewed
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| Scholarly Level |
Faculty
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| Copyright Holder |
Austin Philip H.
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| Rights URI | |
| Aggregated Source Repository |
DSpace
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Rights
Attribution-NonCommercial-NoDerivatives 4.0 International