Measurements of total depletion of ozone in the 2010-2011 Arctic winter lower stratosphere by MIPAS/ENVISAT using a 2D tomographic approach

We present observations of the 2010-2011 Arctic winter stratosphere from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) onboard ENVISAT. We adopted a full 2D tomographic retrieval approach to account for the strong horizontal inhomogeneity of the atmosphere present under vortex conditions. A well isolated stratospheric vortex extended the PSC season up to middle March, with consequent significant activation of heterogeneous chemistry and 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, vortex average ozone showed a daily depletion rate reaching 100 ppbv/day and absolute values dropping to 0.6 ppmv (corresponding to a chemical loss from early winter greater than 80%). In early April, 10% of vortex measurements at 18 km altitude displayed total depletion of ozone. 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. Compared to MIPAS observed 2003-2010 Arctic winters, the lower stratospheric vortex in March had temperature 15 K lower than average, pressure measurements showed a contraction by up to 20% and HNO3 was 50% lower. This resulted in vortex ozone 50% lower than usual and the largest depletion ever observed.