Millimeter wave spectroscopic measurements over the South Pole .4. O-3 and N2O during 1995 and their correlations for two quasi-annual cycles

In two separate papers we have previously reported observations of stratospheric O-3 and N2O over the South Pole during the 1993 annual cycle. Here we present (1) new O-3 and N2O observations at the South Pole in 1995 and (2) correlations between O-3 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 O-3 and N2O. A double-peaked profile again dominates O-3 vertical distribution in 1995 as in 1993. Features such as a pronounced summer-fall decline in mid-stratospheric O-3 followed by an early winter increase, a downward trend in the O-3 contour pattern associated with vertical transport, a transient enhancement of middle to upper stratospheric O-3 just before local sunrise, the timing of the ozone hole onset, and a dramatic increase of stratospheric O-3 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 O-3-N2O correlations to further investigate the double-peaked vertical distribution of O-3. During springtime warmings the O-3/N2O ratio shows a tight coupling between O-3 and N2O around 20 km, as transport creates the low-altitude O-3 peak. A rapid and systematic decrease of the O-3/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 O-3 above -25 km while leaving a transport-produced layer with a relatively large mixing ratio below similar to 25 km. The resulting double-peaked O-3 distribution, which persists for many months, can alter the normally negative correlations between O-3 and N2O in the lower and middle stratosphere, although in measurements of the N2O/O-3 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 O-3 vertical distribution of polar ozone when interpreting O-3-N2O correlations.