Response of middle atmosphere chemistry and dynamics to volcanically elevated sulfate aerosol: Three-dimensional coupled model simulations

The NASA Langley Research Center Interactive Modeling Project for Atmospher ic Chemistry and Transport (IMPACT) model has been used to examine the resp onse of the middle atmosphere to a large tropical stratospheric injection o f sulfate aerosol, such as that following the June 1991 eruption of Mount P inatubo. The influence of elevated aerosol on heterogeneous chemical proces sing was simulated using a three-dimensional climatology of surface area de nsity (SAD) developed using observations made from the Halogen Occultation Experiment, Stratospheric Aerosol and Gas Experiment II, and Stratospheric Aerosol Measurement satellite instruments beginning in June 1991. Radiative effects of the elevated aerosol were represented by monthly mean zonally a veraged heating perturbations obtained from a study conducted with the Euro pean Center/Hamburg (ECHAM4) general circulation model combined with an obs ervationally derived set of aerosol parameters. Two elevated-aerosol simula tions were integrated for 3 1/2 years following the volcanic injection. One simulation included only the aerosol radiative perturbation, and one simul ation included both the radiative perturbation and the elevated SAD. These perturbation simulations are compared with multiple-year control simulation s to isolate relative contributions of transport and heterogeneous chemical processing. Significance of modeled responses is assessed through comparis on with interannual variability. Dynamical and photochemical contributions to ozone decreases are of comparable magnitude. Important stratospheric che mical/dynamical feedback effects are shown, as ozone reductions modulate ae rosol-induced heating by up to 10% in the lower stratosphere and 25% in the middle stratosphere. Dynamically induced changes in chemical constituents which propagate into the upper stratosphere are still pronounced at the end of the simulations.