MILLIMETER-WAVE SPECTROSCOPIC MEASUREMENTS OVER THE SOUTH-POLE .2. AN11-MONTH CYCLE OF STRATOSPHERIC OZONE OBSERVATIONS DURING 1993-1994

A quasi-continuous record of ozone profiles throughout the stratospher e over the South Pole has been obtained over an 11-month cycle, from F ebruary 1993 to January 1994. This record includes the first winter me asurements of ozone profiles in the altitude region above similar to 3 0 km. Observations were made approximately every 3 days, using a high- sensitivity millimeter wave spectrometer to quantitatively measure the pressure-broadened ozone rotational emission line at 276.923 GHz. Ver tical mixing ratio profiles have been derived from pressure-broadened lineshapes by a deconvolution technique. A number of interesting featu res are present. We find a persistent double-peaked structure in the m ixing ratio profiles, lasting through most of the winter period until the remains of the lower peak are destroyed by spring ''ozone hole'' c hemistry. A new low-altitude peak is reformed in December as the vorte x breaks up. With the aid of circumpolar UARS/MLS ozone maps, we inter pret the lower peak as due to transport from ozone-rich regions near t he edge of the continent, while the profile from similar to 30 km upwa rd, composing the ''trough'' region and upper peak, appears to be the result of normal polar summer photochemistry. This double-peaked struc ture then becomes ''fossilized'' within the strong, isolated, fall-win ter vortex. The mixing ratio of the upper peak increases after polar s unset, which we interpret as due to poleward mixing causing an erasure of the negative poleward gradient maintained by photochemistry before sunset. Mixing ratio isopleths show a relatively steady downward tren d for a 3-month period after the winter vortex pattern is established, preceeded by rapid variations in ozone mixing ratios over the 20- to 40-km range. Downward transport rates derived from isopleth slopes in the upper stratosphere are significantly smaller than vertical transpo rt derived from theoretical studies, and we propose an explanation for this discrepancy based on ozone flow from the mesosphere. Descent rat es determined from ozone isopleths in the midstratosphere (25 to 35 km ) are shown to be in good agreement with recent model estimates of dow nward transport in the winter vortex, and with the mid to lower strato spheric descent rate inferred from our own South Pole measurements of N2O. Total column measurements are in generally good agreement with th ose derived from a Dobson photospectrometer at the pole and from local ozonesonde measurements. All three indicate there was no significant increase in total ozone over the pole during the winter of 1993. The o nset of the spring ozone hole over the pole was evident by mid- to lat e August, well before local stratospheric sunrise on September 11, ind icating relatively rapid poleward transport of ozone-depleted air from sunlit regions of the vortex during this period.