ACP Atmospheric Chemistry and Physics ACP Atmos. Chem. Phys. 1680-7324 Copernicus Publications Göttingen, Germany 10.5194/acp-13-2531-2013 Lifetime and production rate of NO<sub>x</sub> in the upper stratosphere and lower mesosphere in the polar spring/summer after the solar proton event in October&ndash;November 2003 Friederich F. 1 von Clarmann T. 1 Funke B. https://orcid.org/0000-0003-0462-4702 2 Nieder H. 1 Orphal J. 1 Sinnhuber M. https://orcid.org/0000-0002-3527-9051 1 Stiller G. P. https://orcid.org/0000-0003-2883-6873 1 Wissing J. M. 3 Karlsruhe Institute of Technology, Institute for Meteorology and Climate Research, Karlsruhe, Germany Instituto de Astrofísica de Andalucía, CSIC, Granada, Spain FB Physik, University of Osnabrück, Osnabrück, Germany 05 03 2013 13 5 2531 2539 Copyright: © 2013 F. Friederich et al. 2013 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://acp.copernicus.org/articles/13/2531/2013/acp-13-2531-2013.html The full text article is available as a PDF file from https://acp.copernicus.org/articles/13/2531/2013/acp-13-2531-2013.pdf

We present altitude-dependent lifetimes of NO<sub>x</sub>, determined with MIPAS/ENVISAT (the Michelson Interferometer for Passive Atmospheric Sounding/the European Environment Satellite), for the Southern polar region after the solar proton event in October–November 2003. Between 50&deg; S and 90&deg; S and decreasing in altitude they range from about two days at 64 km to about 20 days at 44 km. The lifetimes are controlled by transport, mixing and photochemistry. We infer estimates of dynamical lifetimes by comparison of the observed decay to photochemical lifetimes calculated with the SLIMCAT 3-D Model. Photochemical loss contributes to the observed NO<sub>x</sub> depletion by 0.1% at 44 km, increasing with altitude to 45% at 64 km. <br><br> In addition, we show the correlation of modelled ionization rates and observed NO<sub>x</sub> densities under consideration of the determined lifetimes of NO<sub>x</sub>, and calculate altitude-dependent effective production rates of NO<sub>x</sub> due to ionization. For that we compare ionization rates of the AIMOS data base with the MIPAS measurements from 15 October–31 December 2003. We derive effective NO<sub>x</sub>-production rates to be applied to the AIMOS ionization rates which range from about 0.2 NO<sub>x</sub>-molecules per ion pair at 44 km to 0.7 NO<sub>x</sub>-molecules per ion pair at 62 km. These effective production rates are considerably lower than predicted by box model simulations which could hint at an overestimation of the modelled ionization rates.

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