WAVELET ANALYSIS AND VISUALIZATION OF THE FORMATION AND EVOLUTION OF LOW TOTAL OZONE EVENTS OVER NORTHERN SWEDEN

The formation and development of abnormally low total ozone events (LO Es), which typically last an average of 3-4 days, are analyzed to dete rmine conditions under which these events may form. Wavelet analysis i s performed on 13 years of daily total column ozone (TOZ) obtained by the Nimbus-7 Total Ozone Mapping Spectrometer each day of the record. With wavelet analysis, the contributions and relative phases of signal components may be ascertained at specific times of interest. Timescal es relevant during LOEs are identified and the contributions and phase relations of all components present in the TOZ signal are compared fo r common patterns and features. For a location in Sweden, the formatio n of 96% of the 52 LOEs studied required that all components with time scales (tau) less than a maximum value (tau(<)max>) were present in th eir negative phases. This suggests that LOEs result from the simultane ous interaction of TOZ-depleting processes. The number of interacting processes varies with season and location. In addition, two criteria a re seen to prevail when LOEs form in this location. First, background conditions favorable for the development of an event exist; these occu r when TOZ is in a spectral state where all components with Delta tau( i)<tau<tau(max) are in their negative phases. Second, a process takes place that can force the remaining short-timescale components (tau<Del ta tau(i)) into their negative phases. Processes associated with ''ini tiating'' timescales (Delta tau(l)) of approximate to 2-6 days are fou nd to be a key factor in the initiation of LOEs in this location. Alth ough the background conditions are not uncommon, the likelihood that b oth criteria are simultaneously met is low and the occurrence of LOEs is indeed rare (averaging 4.7 events per year from 1980-1990).