A model study on the sulfate aerosol distribution in a deep convective cloud

The interactions between a deep convective cloud system and sulfate aerosols are investigated using a cloud/chemistry model. Sulfate is one of major constituents of the tropospheric aerosols. Our preliminary studies suggest that a deep convective cloud system transports sulfate aerosols into the upper troposphere effectively through its dynamical and microphysical processes in a short time. The ice-phase microphysical processes are suggested to largely contribute to re-distribute sulfate aerosols in such a way that sulfate aerosols get incorporated into the ice-phase hydrometeors through riming following the nucleation of cloud drops and the in-cloud production of sulfate. In this study the mechanisms of the sulfate transport are discussed quantitatively. Moreover, the size dependence of sulfate aerosols that remain in air is discussed. The model used for this study is a non-hydrostatic, quasi-compressible and three-dimensional cloud model with detailed microphysics and explicit sulfur chemistry. The model explicitly represents the size distribution of pre-existing sulfate aerosols. This allows tracing the size dependence of the interactions between water substances and sulfate aerosols. The interactions between sulfur species and the water substances considered are: 1) the equilibrium growth of sulfate aerosols, 2) the nucleation of cloud drops on sulfate aerosols, 3) the absorption of sulfur dioxide by water drops, 4) the oxidation of dissolved sulfur species by hydrogen peroxide to produce sulfate, 5) the impaction scavenging of unactivated interstitial sulfate aerosol by hydrometeors, and 6) the production of new sulfate aerosols by evaporation and sublimation of hydrometeors. The 2 August 1981 CCOPE Supercell storm in Montana is taken as a model convective system for the study.