Impact of the mass-accomodation coefficient on cirrus

Recent laboratory measurements suggest that the mass-accommodation coefficient for ice crystals is smaller than previously thought for typical cirrus environments. To study the possible impacts of this finding, we present a parameterization of the effects of the accommodation coefficient on vapor diffusivity for a bulk ice microphysics model. Initial results of simulations of a subtropical anvil cirrus deck show striking sensistivities to the accommodation coefficient. Clouds simulated with small accommodation coefficients tend to have much larger amounts of small crystals than simulations using larger values or that do not account for the accommodation coefficient. Preliminary studies suggest that the changes in crystal size and amount lead to feedbacks with cloud-radiation interaction and sedimentation that greatly impact cloud dynamics and cloud persistence.