Atmos. Chem. Phys. Discuss., 11, 33191-33227, 2011
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Total depletion of ozone reached in the 2010–2011 Arctic winter as observed by MIPAS/ENVISAT using a 2-D tomographic approach
E. Arnone1, E. Castelli1, E. Papandrea2, M. Carlotti2, and B. M. Dinelli1
1Istituto di Scienza dell'Atmosfera e del Clima – CNR, Bologna, Italy
2Dipartimento di Chimica Fisica e Inorganica, Università di Bologna, Italy

Abstract. We present observations of the 2010–2011 Arctic winter stratosphere from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) onboard ENVISAT. Limb sounding infrared measurements were taken by MIPAS during the Northern polar winter and into the subsequent spring, giving a continuous vertically resolved view of the Arctic dynamics, chemistry and polar stratospheric clouds (PSCs). We adopted a 2-D tomographic retrieval approach to account for the strong horizontal inhomogeneity of the atmosphere present under vortex conditions, self-consistently comparing 2011 to the 2-D analysis of 2003–2010. Unlike most Arctic winters, 2011 was characterized by a strong stratospheric vortex lasting until early April. Lower stratospheric temperatures persistently remained below the threshold for PSC formation, extending the PSC season up to mid-March, resulting in significant chlorine activation leading to ozone destruction. Through inspection of MIPAS spectra, 84% of PSCs were identified as supercooled ternary solution (STS) or STS mixed with nitric acid trihydrate (NAT), 16% formed mostly by NAT particles, and only a few by ice. In the lower stratosphere at potential temperature 450 K, vortex average ozone showed a daily depletion rate reaching 100 ppbv day−1. In early April at 18 km altitude, 10% of vortex measurements displayed total depletion of ozone, and vortex average values dropped to 0.6 ppmv. This corresponds to a chemical loss from early winter greater than 80%. Ozone loss was accompanied by activation of ClO, associated depletion of its reservoir ClONO2, and significant denitrification, which further delayed the recovery of ozone in spring. Sporadic increases of NO2 associated with evaporation of sedimenting PSCs were also observed. Once the PSC season halted, ClO was reconverted into ClONO2. Compared to MIPAS observed 2003–2010 Arctic average values, the 2010–2011 vortex in late winter had 15 K lower temperatures, 40% lower HNO3 and 50% lower ozone, reaching the largest ozone depletion ever observed in the Arctic. The overall picture of this Arctic winter was remarkably closer to conditions typically found in the Antarctic vortex than ever observed before.

Citation: Arnone, E., Castelli, E., Papandrea, E., Carlotti, M., and Dinelli, B. M.: Total depletion of ozone reached in the 2010–2011 Arctic winter as observed by MIPAS/ENVISAT using a 2-D tomographic approach, Atmos. Chem. Phys. Discuss., 11, 33191-33227, doi:10.5194/acpd-11-33191-2011, 2011.
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