Long Term Stratospheric Ozone Changes as simulated by the GSFC 2D Model and Comparisons with Observations

The GSFC two-dimensional (2D) transport and chemistry model has been used for a wide variety of scientific and assessment studies of stratospheric ozone. These model simulations have examined the long term impact on ozone due to various natural and man-made influences. We have recently utilized the long term NCEP and ECMWF ERA-40 meteorological reanalyses data sets, available for the 1950s to the present, to derive yearly varying zonal mean transport fields for input into the model. This allows us to account for the interannual changes in dynamics and temperature in the model calculations. Our results show that the model can resolve much of the interannual variability observed in the TOMS total ozone data on a global basis, including a dominant QBO in the tropics, and QBO-like signals at midlatitudes. This capability then allows us to run numerous model sensitivity simulations to separate the various effects that influence ozone, including the interannual variability, halogen increases at the surface, the stratospheric sulfate aerosol loading, and ultraviolet flux variations due to the 11-year solar cycle. In this study, we will examine these model calculations of long term changes of ozone at midlatitudes due to the various natural and man-made factors, and how these compare with the changes observed in the TOMS total ozone data record for the late 1970s to the present.