Abstract
Influence of low-level wind speed on droplet spectra near cloud base in trade wind cumulus
Department of Atmospheric Sciences, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
Department of Atmospheric Sciences, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
Earth Observation Laboratory, National Center for Atmospheric Research, Boulder, Colorado, USA
Data collected during the Rain In Cumulus over the Ocean (RICO) campaign demonstrate a relationship between the low-level wind speed, droplet concentrations and the presence of large cloud droplets near cloud base in trade wind clouds in a clean marine background atmosphere. Weak winds were associated with fewer activated cloud droplets, larger mean droplet sizes, and more large cloud droplets, even though the concentration of giant/ultragiant sea-salt aerosol increased with increasing near-surface wind speed. The data suggest that in unpolluted trade wind cumuli: (1) the production of large cloud droplets near cloud base is controlled primarily by the intensity of the cloud base updraft rather than the concentration of giant/ultragiant sea-salt particles; (2) higher droplet concentrations are more likely under conditions of stronger low-level wind speeds, primarily because stronger low-level wind speeds are associated with more intense cloud base updrafts.
Received 6 July 2006; accepted 20 September 2006; published 26 October 2006.
Citation: (2006), Influence of low-level wind speed on droplet spectra near cloud base in trade wind cumulus, Geophys. Res. Lett., 33, L20814, doi:10.1029/2006GL027487.
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