Comparison of empirically derived ozone losses in the Arctic vortex

Abstract

A number of studies have reported empirical estimates of ozone loss in the Arctic vortex. They have used satellite and in situ measurements and have principally covered the Arctic winters in the 1990s. While there is qualitative consistency between the patterns of ozone loss, a quantitative comparison of the published values shows apparent disagreements. In this paper we examine these disagreements in more detail. We choose to concentrate on the five main techniques (Match, Système d'Analyse par Observation Zénithale (SAOZ)/REPROBUS, Microwave Limb Sounder (MLS), vortex average descent, and the Halogen Occultation Experiment (HALOE) ozone tracer approach). Estimates of the ozone losses in three winters (1994/1995, 1995/1996 and 1996/1997) are recalculated so that the same time periods, altitude ranges, and definitions of the Arctic vortex are used. This recalculation reveals a remarkably good agreement between the various estimates. For example, a superficial comparison of results from Match and from MLS indicates a big discrepancy (2.0 ± 0.3 and 0.85 ppmv, respectively, for air ending at ∼460 K in March 1995). However, the more precise comparisons presented here reveal good agreement for the individual MLS periods (0.5 ± 0.1 versus 0.5 ppmv; 0.4 ± 0.2 versus 0.3–0.4 ppmv; and 0.16 ± 0.09 ppmv versus no significant loss). Initial comparisons of the column losses derived for 1999/2000 also show good agreement with four techniques, giving 105 DU (SAOZ/REPROBUS), 80 DU (380–700 K partial column from Polar Ozone and Aerosol Monitoring (POAM)/REPROBUS), 85 ± 10 DU (HALOE ozone tracer), and 88 ± 13 (400–580 partial column from Match). There are some remaining discrepancies with ozone losses calculated using HALOE ozone tracer relations; it is important to ensure that the initial relation is truly representative of the vortex prior to the period of ozone loss.