Millimeter wave spectroscopic measurements over the South Pole 4. O < inf> 3 and N < inf> 2 O during 1995 and their correlations for two quasi-annual cycles

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In two separate papers we have previously reported observations of stratospheric O3 and N2O over the South Pole during the 1993 annual cycle. Here we present (1) new O3 and N2O observations at the South Pole in 1995 and (2) correlations between O3 and N2O for two 11-month observations during February 1993 to January 1994 and January-December 1995. Strong similarities exist between the two quasi-annual cycles for both O3 and N2O. A double-peaked profile again dominates O3 vertical distribution in 1995 as in 1993. Features such as a pronounced summer-fall decline in mid-stratospheric O3 followed by an early winter increase, a downward trend in the O3 contour pattern associated with vertical transport, a transient enhancement of middle to upper stratospheric O3 just before local sunrise, the timing of the ozone hole onset, and a dramatic increase of stratospheric O3 during and following vortex breakup all show good consistency between the two annual cycles. N2O observations show a good agreement between the two 11-month cycles in atmospheric descent rate during fall and winter, and in the timing of N2O recovery from diminished values during spring. We use O3-N2O correlations to further investigate the double-peaked vertical distribution of O3. During springtime warmings the O3/N2O ratio shows a tight coupling between O3 and N2O around 20 km, as transport creates the low-altitude O3 peak. A rapid and systematic decrease of the O3/N2O ratio during summer in the 25 to 30 km region (while N2O is essentially stable) supports the increasingly dominant role of photochemistry in producing the vertical profile for O3 above ∼25 km while leaving a transport-produced layer with a relatively large mixing ratio below ∼25 km. The resulting double-peaked O3 distribution, which persists for many months, can alter the normally negative correlations between O3 and N2O in the lower and middle stratosphere, although in measurements of the N2O/O3 ratios for polar air these perturbations have often been taken to be a hallmark of catalytic ozone depletion by chlorine. The present analysis should help to clarify the influence of the relatively unique O3 vertical distribution of polar ozone when interpreting O3-N2O correlations.

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Journal of Geophysical Research Atmospheres