A study showing impacts of aerosols on clouds and precpitation associated with a large winter cyclone (Invited Presentation)
To address a very complex and uncertain research problem that affects storms from convective to climate scales, the Thompson et al (2008) bulk microphysics scheme was recently updated to incorporate aerosols explicitly. The scheme explicitly nucleates water and ice from their dominant respective nuclei and fully tracks and predicts the number of available aerosols. Using the Weather Research and Forecasting (WRF) model, the scheme was tested in a very high resolution (4-km spacing) simulation of a three-day winter storm event over the entire contiguous U.S. A control simulation was run with climatological aerosol conditions and then two sensitivity experiments with very clean and very polluted conditions were used to evaluate the magnitude of aerosol-cloud-precipitation interactions.
Analysis of these sensitivity experiments clearly shows the expected change to water droplet populations, including both large and small droplets. Less well documented changes to liquid water content and mean size as a function of temperature occur as well, which has interesting implications to frequency and severity of aircraft icing that go beyond the usual findings associated with surface precipitation impacts. Furthermore, we found that aerosols impacted the relative fraction of liquid versus ice phase of the surface precipitation which has implications for the extent and severity of a severe surface ice storm.