A new approach to the characterization of long-term changes in total atmospheric ozone: Determination and application of frequency distributions

Abstract

This paper sets forth a new approach for describing long-term changes in total ozone by using frequency distributions and analyzing the extreme values. We applied this methodology to the database of column ozone provided by the Total Ozone Mapping Spectrometer aboard Nimbus 7. We examined a geographic region measuring 7.0° in latitude by 6.25° in longitude in the midwestern United States from 1979 to 1991. On any given spring day, individual ozone measurements in this region show a large variability, where the differences between the local noon maximum and minimum total ozone values sometimes exceed 100 Dobson units. Daily variability in total column ozone was shown to be greater in the spring than in the fall. Based on frequency distribution results, the most probable values for the spring season decreased from 1979–1982 to 1989–1991. During spring, the frequency of extremely low ozone values decreased from the six-year period 1980–1985 to the 1986–1991 time period, while the opposite situation prevailed during fall. Preliminary results indicate that this approach can illuminate the detailed behavior of TOZ within each season in a particular region.