Analysis of SAGE II observations using data assimilation by the SUNY-SPB two-dimensional model and comparison to TOMS data

The two-dimensional SUNY-SPB chemical-transport model is used to assimilate SAGE II 1985-1993 ozone, water vapor, and aerosol data. Combining the observations and model calculations allows one to fill in significant gaps in the SAGE II altitude-latitude cross sections; to correct the SAGE II data using data assimilation quality control procedures and to compare SAGE II measurements to independent TOMS observations of column ozone. The model/data assimilation was used for the analysis of ozone behavior for the period 1980-1995. Diagnostics of the observed variability of the total ozone content for 1980-1995 have been carried out using this procedure. The obtained results demonstrate that the negative trend in total ozone, which has been observed during the last several years, was a result of ozone destruction by the chlorine and bromine catalytic cycles, mainly in two height regions: near 20 and 40 km. The percent changes of ozone concentration are approximately similar in both height regions (with a maximum loss of 8-12%). However, the total ozone variability was 1 order of magnitude larger near 20 km than near 40 km. These calculations strengthen the hypothesis that heterogeneous processes on aerosol surfaces have played the dominant role in the observed variability of total ozone during the 1980-1995 period. No solar cycle effects were included in the assimilation model for this study.