A NEW APPROACH TO THE CHARACTERIZATION OF LONG-TERM CHANGES IN TOTAL ATMOSPHERIC OZONE - DETERMINATION AND APPLICATION OF FREQUENCY-DISTRIBUTIONS

This paper sets forth a new approach for describing long-term changes in total ozone by using frequency distributions and analyzing the extr eme values. We applied this methodology to the database of column ozon e provided by the Total Ozone Mapping Spectrometer aboard Nimbus 7. We examined a geographic region measuring 7.0 degrees in latitude by 6.2 5 degrees in longitude in the midwestern United States from 1979 to 19 91. On any given spring day, individual ozone measurements in this reg ion show a large variability, where the differences between the local noon maximum and minimum total ozone values sometimes exceed 100 Dobso n units. Daily variability in total column ozone was shown to be great er in the spring than in the fall. Based on frequency distribution res ults, the most probable values for the spring season decreased from 19 79-1982 to 1989-1991. During spring the frequency of extremely low ozo ne values decreased from the six-year period 1980-1985 to the 1986-199 1 time period, while the opposite situation prevailed during fall. Pre liminary results indicate that this approach can illuminate the detail ed behavior of TOZ within each season in a particular region.