Numerical models that simulate the circulation of the atmosphere have been used to gain insight into atmospheric phenomena and to make predictions of its future state since the 1950s. Ever increasing computing power have allowed for the development of three-dimensional global chemistry-transport models (CTMs) and the inclusion of an ever more explicit treatment of physical and chemical processes (such as more detailed chemical mechanisms, boundary layer and cloud coupling, and the combination of tropospheric chemistry with climate modeling). A key upper boundary condition, and long-standing problem, for these models is the stratosphere, which controls the flux of ozone into the troposphere as well as the ultraviolet radiation field driving the photochemistry. The large uncertainty in the current model estimations of the cross-tropopause ozone flux (from less than 400 Tg/year to over 1400 Tg/year) can give almost opposite interpretations of the role of tropospheric photochemistry.

I am now utilizing a global CTM model called Impact to study the exchange of trace species between the troposphere and stratosphere. The Impact model is an advanced model system developed at the Lawrence Livermore National Laboratory and is driven by the NASA Data Assimilation Office (DAO) meteorological data. The high vertical resolution of the model (46 levels with model top at 0.1 hPa) could make it possible to study the tropospheric and stratospheric photochemistry and the exchange of trace species between the troposphere and stratosphere. I have used the Impact model framework and added the chemistry of sulfate, soil dust and biomass burning aerosols to the model. I am now using this aerosol version of Impact to study the dispersion of Mt. Pinatubo volcanic clouds and their downward transport to the troposphere and their final deposition onto the ground. The eruption of Mt. Pinatubo is believed to be the largest aerosol perturbation to the stratosphere in the 20th century with about 20 Tg SO2 emitted into the lower stratosphere. The erupted SO2 was converted to H2SO4 aerosol with a lifetime of about 35 days. The detailed observations of Mt. Pinatubo aerosol clouds both from Satellites (such as the NASA SAGE-II instrument) and ground-based instruments provided us with an excellent opportunity to study the behavior of model-simulations of stratosphere/troposphere exchange by comparing our model simulations with the measurement data.

My future plans include studying the tropospheric sulfur cycle and tropospheric photochemistry using the Impact model with aerosols, and studying the indirect forcing of anthropgenic aerosols on climate through the modification of cloud properties by aerosols.

My current computational needs: I am now running my jobs on the T3E parallel machine (NERSC/MCURIE). I have installed the Impact model on the J90 machine (Seymour). I am running the jobs on a single processor on Seymour. I plan to port my codes from the T3E to the NERSC's IBM SP to run some jobs there.