One Dimension is All You Need: Coupling Turbulence to Cloud-Aerosol Interactions

Laboratory convection cloud chambers (such as the Pi Chamber at Michigan Technological University) produce supersaturation by turbulent mixing of saturated air parcels that have different temperatures. The parcels originate from the warm saturated lower surface and the cool saturated upper surface. A steady state is easy to obtain in such a chamber when aerosols are continuously injected and a balance is achieved between aerosol injection and droplet growth and droplet fallout. Turbulence in the convection chamber creates fluctuations in both temperature and water vapor, inducing variations in supersaturation. These supersaturation variations affect droplet activation and growth that are specific to individual aerosol species. Furthermore, the activation, growth and fallout of cloud droplets regulates supersaturation. To better understand cloud-aerosol interactions in a turbulent environment, we introduce "Cloudy-T", a one-dimensional model of turbulence based on Wunsch and Kerstein (2005). Cloudy-T is a unique model because it couples the dynamics of individual droplet growth, fully resolved temperature/water vapor fields, and turbulent fluctuations at all relevant scales in a computationally economical framework. Cloudy-T is suitable for testing how aerosol species, number concentration, and turbulence intensity interact to create different droplet size distributions in a convection cloud chamber.

Cloudy-T was developed to complement experiments from the Pi Chamber at Michigan Tech University, a turbulent cloud chamber. ODT shows good agreement with the chamber measurements for first order microphysical properties such as number concentration and mean radius. In addition to describing Cloudy-T, we will also present its application to the interesting problem of bimodal DSDs that have been both observed in the Pi Chamber and simulated with Cloudy-T (as shown in the graphic), and whose origins we are investigating.