Ozone depletion in Northern Hemisphere winter/spring 1999/2000 as measured by the Global Ozone Monitoring Experiment on ERS-2

During the SOLVE/THESEO 2000 campaign the Global Ozone Monitoring Experiment (GOME) sampled the Arctic region from January to April 2000. Results from the GOME total ozone measurements are presented to highlight the peculiarity of the 1999/2000 Arctic winter/spring season in relation to earlier years. Chemical ozone loss calculations have been derived from daily vortex-averaged ozone profile measurements from GOME. Between 12 February and 13 March 2000, an accumulated chemical ozone loss of 1.3 +/- 0.3 ppmv at 475 K isentropic height was derived within the polar vortex. This amounts to a daily chemical depletion rate of 43 ppbv per day (42%). Using 25 January 2000 as a reference date, where six GOME ozone profile measurements were available, an ozone loss of 1.8 +/- 0.4 ppmv (49%, 37 ppbv/day) can be derived. The GOME vortex average ozone volume mixing ratios at 475 K agrees well with results from the three-dimensional chemical transport model SLIMCAT and weekly mean values derived from higher-resolution ozone sonde measurements. The low vertical resolution of the GOME measurements leads to an overestimation of ozone after the vortex was split into parts in the middle of March. The accumulated chemical column loss (400-600 K) corrected for diabatic effects is 114 +/- 10 DU between 25 January and 13 March. By comparing midlatitude ozone volume mixing ratios from GOME to passive ozone tracer data from SLIMCAT, an ozone loss of about 12% is estimated at 475 K isentropic level within the potential vorticity range between 20 and 30 PVU. This value is statistically insignificant because of uncertainties in model transport.