POAM-II OZONE OBSERVATIONS IN THE ANTARCTIC OZONE HOLE IN 1994, 1995,AND 1996

We present an overview of Polar Ozone and Aerosol Measurement (FOAM) I I satellite-based observations of ozone in the Antarctic ozone hole in 1994, 1995, and 1996. The FOAM II observations are consistent with pr evious observations suggesting that ozone loss in the ozone hole is co nfined to the polar vortex. Ozone concentrations are observed to decre ase by nearly a factor of 10 near 20 km during the ozone hole formatio n period, and a reduction in ozone was observed up to 24 km. The timin g of ozone loss and recovery was similar in each year. Ozone concentra tions begin to decrease in July, and the period of largest depletion o bserved by FOAM II occurs between early September and early October, w hen the observations are obtained at high southern latitudes (82(0)-88 (0)S) near the vortex center. However, ozone concentrations were consi stently lower (by about 10%) in 1996, throughout the atone hole altitu de region and time period, than in the other two years. We have also u sed the POAM II observations to compute vertical profiles of monthly a veraged ozone photochemical loss rates as a function of potential temp erature in August (450-800 K); and September (450-700 K) of each year, incorporating a correction for diabatic descent. We find that the ozo ne loss rates are not significantly different from zero in August 1994 at any potential temperature level. However, we do find significant c hemical loss in August 1995 below 600 K, and in August 1996 at all lev els up to 700 K. Maximum monthly averaged ozone chemical loss rates oc curred in September near 500 K in each year (1994: 0.1 +/- 0.004 parts per million by volume per day (ppmv/d); 1995 and 1996: 0.08 +/- 0.004 ppmv/d). Generally, in September, loss rates were larger in 1994 than in 1995 and 1996 below 550 K, and above 550 K the largest loss rates occurred in 1996. We find significant chemical loss up to at least 706 K in September in all three years. Finally, the FOAM II observations show that in late spring, after the ozone hole chemical processing has been completed, ozone mixing ratios are lower inside the Antarctic vo rtex (relative to outside the vortex) at all levels between at least 4 50 K and 1500 K, presumably resulting from a combination of dynamical and chemical effects.