Drop Size Distributions and the Efficiency of Nucleation Scavenging over the Hardiman Fire

A prescribed burn experiment was conducted in Hardiman Township, Ontario, Canada in August 1987. The fire was of adequate intensity to force the formation of a cumulus cloud, and much of the smoke passed through this cloud. The evolution of the aerosol and drop size distributions within this fire-driven cloud due to nucleation and condensation was calculated by a microphysical entraining model. We investigate the sensitivity of nucleation scavenging and drop number density to the different environmental aerosol distributions. The predicted drop size distribution and the measured data above the fire are in good agreement for drop sizes which correspond to condensation on the measured aerosol spectra. The results from this study can be used to develop a parameterization that relates the drop number to the updraft velocity and the aerosol number at cloud base. We plan to extend this study to predict the effects of aerosols on drop spectra for use in climate models.