Ozone loss in the 2002–2003 Arctic vortex deduced from the assimilation of Odin/SMR O 3 and N 2 O measurements: N 2 O as a dynamical tracer

In this paper we investigate the evolution of the northern polar vortex during the winter 2002–2003 in the lower stratosphere by using assimilated fields of ozone (O 3 ) and nitrous oxide (N 2 O). Both O 3 and N 2 O used in this study are obtained from the Sub‐Millimetre Radiometer (SMR) aboard the Odin satellite and are assimilated into the global three‐dimensional chemistry transport model of Météo‐France, MOCAGE. O 3 is assimilated into the ‘full’ model including both advection and chemistry whereas N 2 O is only assimilated with advection since it is characterized by good chemical stability in the lower stratosphere. We show the ability of the assimilated N 2 O field to localize the edge of the polar vortex. The results are compared to the use of the maximum gradient of modified potential vorticity as a vortex edge criterion. The O 3 assimilated field serves to evaluate the ozone evolution and to deduce the ozone depletion inside the vortex. The chemical ozone loss is estimated using the vortex‐average technique. The N 2 O assimilated field is also used to substract out the effect of subsidence in order to extract the actual chemical ozone loss. Results show that the chemical ozone loss is 1.1 ± 0.3 ppmv on the 25 ppbv N 2 O level between mid‐November and mid‐January, and 0.9 ± 0.2 ppmv on the 50 ppbv N 2 O level between mid‐November and the end of January. A linear fit over the same periods gives a chemical ozone loss rate of ∼18 ppbv day −1 and ∼9.3 ppbv day −1 on the 25 ppbv and 50 ppbv N 2 O levels, respectively. The vortex‐averaged ozone loss profile from the O 3 assimilated field shows a maximum of 0.98 ppmv at 475 K. Comparisons to other results reported by different authors using different techniques and different observations give satisfactory results. Copyright © 2008 Royal Meteorological Society