Editorial Type:
Article
Article Type:
Research Article

Progress on Predicting the Breadth of Droplet Size Distributions Observed in Small Cumuli

Jennifer L. Bewley Department of Earth and Atmospheric Sciences, Purdue University, West Lafayette, Indiana

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Sonia Lasher-Trapp Department of Earth and Atmospheric Sciences, Purdue University, West Lafayette, Indiana

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Print Publication:
01 Dec 2011
DOI:
https://doi.org/10.1175/JAS-D-11-0153.1
Page(s):
2921–2929
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Abstract

A modeling framework representing variations in droplet growth by condensation, resulting from different saturation histories experienced as a result of entrainment and mixing, is used to predict the breadth of droplet size distributions observed at different altitudes within trade wind cumuli observed on 10 December 2004 during the Rain in Cumulus over the Ocean (RICO) field campaign. The predicted droplet size distributions are as broad as those observed, contain similar numbers of droplets, and are generally in better agreement with the observations when some degree of inhomogeneous droplet evaporation is considered, allowing activation of newly entrained cloud condensation nuclei. The variability of the droplet growth histories, resulting primarily from entrainment, appears to explain the magnitude of the observed droplet size distribution widths, without representation of other broadening mechanisms. Additional work is needed, however, as the predicted mean droplet diameter is too large relative to the observations and likely results from the model resolution limiting dilution of the simulated cloud.

Corresponding author address: Sonia Lasher-Trapp, 550 Stadium Mall Drive, West Lafayette, IN 47907-2051. E-mail: slasher@purdue.edu

Abstract

A modeling framework representing variations in droplet growth by condensation, resulting from different saturation histories experienced as a result of entrainment and mixing, is used to predict the breadth of droplet size distributions observed at different altitudes within trade wind cumuli observed on 10 December 2004 during the Rain in Cumulus over the Ocean (RICO) field campaign. The predicted droplet size distributions are as broad as those observed, contain similar numbers of droplets, and are generally in better agreement with the observations when some degree of inhomogeneous droplet evaporation is considered, allowing activation of newly entrained cloud condensation nuclei. The variability of the droplet growth histories, resulting primarily from entrainment, appears to explain the magnitude of the observed droplet size distribution widths, without representation of other broadening mechanisms. Additional work is needed, however, as the predicted mean droplet diameter is too large relative to the observations and likely results from the model resolution limiting dilution of the simulated cloud.

Corresponding author address: Sonia Lasher-Trapp, 550 Stadium Mall Drive, West Lafayette, IN 47907-2051. E-mail: slasher@purdue.edu
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