Influence of Microphysical Variability on Stochastic Condensation in a Turbulent Laboratory Cloud

Influence of Microphysical Variability on Stochastic Condensation in a Turbulent Laboratory Cloud AbstractDiffusional growth of droplets by stochastic condensation and a resulting broadening of the size distribution has been considered as a mechanism for bridging the cloud droplet growth gap between condensation and collision-coalescence. Recent studies have shown that supersaturation fluctuations can lead to a broadening of the droplet size distribution at the condensational stage of droplet growth. However, most studies using stochastic models assume the phase relaxation time of a cloud parcel to be constant. In this paper we ask how do variability in droplet number concentration and radius influence the phase relaxation time? And what effect does it have on the droplet size distributions? To answer these questions, we created steady state cloud conditions in the laboratory and used digital inline holography to directly observe the variations in local number concentration and droplet size distribution and, thereby, the integral radius. We also extend the stochastic equations to account for fluctuations in integral radius and obtain new terms that are compared with the laboratory observations. We find that the variability in integral radius is primarily driven by variations in the droplet number concentration and not the droplet radius. This variability does not contribute significantly to the mean droplet growth rate, but contributes significantly to the rate of increase of the size distribution width. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of the Atmospheric Sciences American Meteorological Society

Influence of Microphysical Variability on Stochastic Condensation in a Turbulent Laboratory Cloud

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Publisher
American Meteorological Society
Copyright
Copyright © American Meteorological Society
ISSN
1520-0469
D.O.I.
10.1175/JAS-D-17-0158.1
Publisher site
See Article on Publisher Site

Abstract

AbstractDiffusional growth of droplets by stochastic condensation and a resulting broadening of the size distribution has been considered as a mechanism for bridging the cloud droplet growth gap between condensation and collision-coalescence. Recent studies have shown that supersaturation fluctuations can lead to a broadening of the droplet size distribution at the condensational stage of droplet growth. However, most studies using stochastic models assume the phase relaxation time of a cloud parcel to be constant. In this paper we ask how do variability in droplet number concentration and radius influence the phase relaxation time? And what effect does it have on the droplet size distributions? To answer these questions, we created steady state cloud conditions in the laboratory and used digital inline holography to directly observe the variations in local number concentration and droplet size distribution and, thereby, the integral radius. We also extend the stochastic equations to account for fluctuations in integral radius and obtain new terms that are compared with the laboratory observations. We find that the variability in integral radius is primarily driven by variations in the droplet number concentration and not the droplet radius. This variability does not contribute significantly to the mean droplet growth rate, but contributes significantly to the rate of increase of the size distribution width.

Journal

Journal of the Atmospheric SciencesAmerican Meteorological Society

Published: Nov 9, 2017

References

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