The Influence of Biogenic Aerosols on Cloud Microphysics

The influence of the physical and chemical characteristics of biogenic aerosols on convective clouds was determined using a two-dimensional cloud resolving model with spectral bin microphysics. The aerosols and metrological conditions included in the simulations were representative of central Virginia, where strong biogenic hydrocarbon emissions create high levels of secondary organic aerosol during summer. The response of a convective cloud to such aerosols was determined relative to a control simulation in which ammonium sulfate aerosols were activated using traditional Kohler theory. The cloud perturbation from biogenic aerosols was determined by including measurements of their physical and chemical characteristics into the model and by applying a modified version of Kohler theory that describes the activation of internally mixed aerosols. Metrics of cloud perturbation investigated in this study include changes in cloud droplet number, ice crystal number, rain water amount, ice mass, cloud reflectivity, cell lifetime, accumulated rainfall, stratiform versus convective rain amount, cloud top height, and the amount and distribution of latent heating.