A study of ozone depletion in the 2004/2005 Arctic winter based on data from Odin/SMR and Aura/MLS

Ozone depletion in the colder than average 2004/2005 Arctic polar vortex is mapped and quantified using ozone profiles from two limb sounding satellite instruments, the Earth Observing System Microwave Limb Sounder (Aura/MLS) and the Odin Sub-Millimetre Radiometer (Odin/SMR). Profiles of chemically inert nitrous oxide (N2O) are used to trace vertical transport during the winter. Two methods are used for estimating the vortex average ozone losses north of 67 degrees equivalent latitude. In a first step, the time evolution of ozone mixing ratios is described on N2O isopleths. Maximum ozone depletion is found on the 100 ppbv and 150 ppbv N2O isopleths (located in the 430-460 K potential temperature range in mid-March 2005) where vortex average ozone depletion totalled 1.0-1.1 ppmv for Aura/MLS and 0.7-0.9 ppmv for Odin/SMR. Second, ozone profiles from Aura/MLS and Odin/SMR are assimilated into the DIAMOND isentropic transport model. Ozone depletion is estimated by comparing assimilated fields to ozone fields passively transported from 1 January. On the 450 K potential temperature level, the Aura/MLS ozone fields indicate 0.9-1.3 ppmv vortex-averaged ozone depletion while the Odin/SMR fields indicate 0.6-0.9 ppmv depletion. The uncertainty depends mainly on the rates of cross-isentropic transport used in the study. The ozone depletion estimates in this study are lower than previously published estimates. The discrepancies to some studies can be attributed to the more adequate treatment of an ozone poor region that is found in the central polar vortex in the early winter.