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We present altitude-dependent lifetimes of NOx, determined withMIPAS/ENVISAT (the Michelson Interferometer for Passive Atmospheric Sounding/the European Environment Satellite), for the Southern polar region after the solar proton event inOctober–November 2003. Between 50° S and 90° S anddecreasing in altitude they range from about two days at 64 km to about 20days at 44 km. The lifetimes are controlled by transport, mixing andphotochemistry. We infer estimates of dynamical lifetimes by comparison ofthe observed decay to photochemical lifetimes calculated with the SLIMCAT 3-DModel. Photochemical loss contributes to the observed NOx depletion by0.1% at 44 km, increasing with altitude to 45% at 64 km. In addition, we show the correlation of modelled ionization rates and observedNOx densities under consideration of the determined lifetimes of NOx, andcalculate altitude-dependent effective production rates of NOx due toionization. For that we compare ionization rates of the AIMOS data base withthe MIPAS measurements from 15 October–31 December 2003. We deriveeffective NOx-production rates to be applied to the AIMOS ionization rateswhich range from about 0.2 NOx-molecules per ion pair at 44 km to 0.7 NOx-molecules per ion pair at 62 km. These effective production rates areconsiderably lower than predicted by box model simulations which could hintat an overestimation of the modelled ionization rates

atmospheric chemistry and physics

Lifetime and production rate of NO&amp;lt;sub&amp;gt;x&amp;lt;/sub&amp;gt; in the upper stratosphere and lower mesosphere in the polar spring/summer after the solar proton event in October–November 2003