Relationship Between Climate Variability and Total Ozone Change in the Northern Mid-Latitudes

Traditionally, long-term changes (trends) in the total ozone amount at Northern mid-latitudes have been derived from zonal averages made over the latitude range from 25 to 60( N. We separate the total ozone field into four meteorological regimes, (1) a tropical regime south of the subtropical upper troposphere front; (2) a mid-latitude regime between the sub-tropical and the polar fronts; (3) a polar regime between the polar front and the arctic front (the polar vortex), (4) an arctic regime, north of the arctic front. The total ozone distribution within the first three regimes is quite narrow, with a width of about three per cent of the mean value. We also find that the mean value within these regimes is relatively constant from year to year. Thus the mean total ozone value that is observed between 25 to 60( N is mainly governed by the relative areas of the three regimes within these latitude limits. We find that during the period from 1978 to 1992 the area of the tropical regime increased while that of the polar regime decreased. We conclude that most of the northern mid-latitude trend in the total ozone record between 1978 and 1992 is the result of a northward movement of the mean latitude of both the subtropical and polar fronts. As there is a distinct tendency for the surface pressure systems to follow the flows aloft, e.g. the jet streams embedded in these fronts, any movement in the mean positions of the upper troposphere fronts will result in a change in the climate of the Northern hemisphere. Thus changes in climate, both short term and long-term, and the measured stratospheric ozone trends and variability at mid-latitudes are closely linked.