Seminar

Abstract

On June 15th, 1991 the eruption of Mt. Pinatubo in the Philippines injected about 20 Tg of sulfur dioxide into the stratosphere. The sulfur dioxide was transformed into sulfuric acid aerosol and increased the amount of background aerosol by orders of magnitude. The volcanic aerosol remained in the stratosphere for about three years, inducing a perturbation of the dynamics and chemistry of the stratosphere. We simulate the Mt. Pinatubo eruption with the Goddard Earth Observing System (GEOS) version 5 general circulation model, coupled to the GOCART aerosol module and the StratChem stratospheric chemistry module. The total optical depth from our simulations is in good agreement with SAGE-II and AVHRR data. In our simulations, the volcanic aerosol interacts with radiation, modifying the simulated meteorology, and with the stratospheric chemistry, by providing surface area for heterogeneous reactions. We describe the changes in the dynamics and chemical composition of the stratosphere induced by the absorption of longwave radiation by the aerosol from Mt. Pinatubo. The absorption of longwave radiation by the volcanic cloud induces a strong increase in the upwards-vertical winds at tropical latitudes, and a divergent motion southward and northward from the latitude of the eruption. On the other hand, the additional aerosol surface area available for heterogeneous chemistry leads to an increase in ozone in the middle stratosphere and a decrease in the lower stratosphere. We will show how the perturbation to both the stratospheric dynamics and the stratospheric chemistry are needed to explain the changes in ozone concentrations detected after the eruption of Mt. Pinatubo.