Laboratory Investigations of Aerosol-Cloud Interactions in an Entraining, Turbulent Environment

Abstract

Every cloud droplet in Earth’s atmosphere formed on a preexisting mote of dust – an aerosol particle. Such aerosol-cloud interactions are crucial elements of Earth’s climate system, and they must be understood and reliably represented in models of the atmosphere (for example, for predicting weather). One of the factors that governs how aerosol particles determine cloud properties is how clouds mix with surrounding air, a process called entrainment. We propose to conduct laboratory experiments of aerosol-cloud interactions in a setting in which we can measure the effects of entrainment. Preliminary results from our novel experimental facility, Michigan Technological University’s Pi Chamber, show that as the fraction of air that is mixed into the cloud increases, the width of the cloud droplet size distribution increases, and the fraction of aerosol particles that become cloud droplets decreases. These two effects have implications for the formation of precipitation. We will conduct measurements of the effects of entrainment on aerosol-cloud interactions in this laboratory setting where we can control and verify entrainment independently. We will use a large eddy simulation model that we have developed for the chamber to investigate processes that we cannot directly measure. Finally, we will compare data from these experiments and simulations to data from field campaigns where entrainment is suspected to be playing a role.