Ozone Variations over Midlatitudes and on the Global Scale

Several sets of satellite and ground-based measurements are currently available for the examination of temporal and latitudinal variations and long-term changes of ozone. All data sets show changes in the rate of the total ozone decline in recent years. While global ozone was fairly constant during the 1990s, the average values of the 1990s are about 3% lower than those of the late 1970s. About 38% of the global ozone is located between 25S and 25N where the data show no decline. In the 35-60N zone, the strongest decline occurs during the winter-spring season; the decline in autumn is much smaller there. Temporal autocorrelations of monthly mean total ozone anomalies over the 35-60S and 35-60N latitude bands reveal that anomalies established during the wintertime midlatitude ozone buildup persist until the end of autumn, and then are rapidly erased once the next winter's buildup begins. Short-term variations in springtime midlatitude ozone demonstrate only a modest correlation with springtime polar ozone variations. However by early summer, ozone variations throughout the extratropics are highly correlated. Long-term total ozone trends at middle and high latitudes are also different for spring and nearly identical for summer. About 39% of the observed southern midlatitude ozone decline in December can be attributed to the polar ozone depletion up to November. In the northern hemisphere, the corresponding contribution is about 15%, but the error bars are too large to make an accurate estimate.