A Marine Stratus Layer Modified by Nuclei from a Ship Plume

Abstract

On 13 July 1991, a steaming ship produced a long, linear feature in a marine stratus layer offshore Baja California, detected in a 2207 UTC NOAA-11 3.7-µ m satellite image. Droplet sizes were inferred from the satellite image: small droplets existed in the linear feature, and larger droplets existed in the adjacent ambient region. A one-dimensional cloud formation model was used to investigate the contributions of measured cloud condensation nuclei (CCN) and assumed updrafts to the formation of droplets in the ambient cloud and embedded linear feature. The results indicate that 1) the ambient CCN and ambient updraft could explain the large droplets detected in the ambient stratus, 2) the elevated CCN measured in the ship plume and the assumed ambient updraft could explain small droplets detected in the linear feature, and 3) the ambient CCN and assumed ship-enhanced updraft could not explain the small droplets in the linear feature. The measured ship-produced nuclei appear to have caused the observed cloud modification; the assumed ship-produced updraft played only a minor role, if any.