Lifetime and production rate of NOx in the upper stratosphere and lower mesosphere in the polar spring/summer after the solar proton event in October–November 2003
1Karlsruhe Institute of Technology, Institute for Meteorology and Climate Research, Karlsruhe, Germany
2Instituto de Astrofísica de Andalucía, CSIC, Granada, Spain
3FB Physik, University of Osnabrück, Osnabrück, Germany
Abstract. We present altitude dependent lifetimes of NOx, determined with MIPAS/ENVISAT, for the southern polar region after the solar proton event in October–November 2003. Varying in latitude 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 photolysis. We infer dynamical lifetimes by comparison of the observed decay to photolytical lifetimes calculated with the SLIMCAT 3-D Model. Photochemical loss contributes to the observed NOx depletion by 10% at 44 km, increasing with altitude to 35% at 62 km at a latitude of –63° S. At higher latitudes, the contribution of photochemical loss can be even more important.
In addition, we show the correlation of modeled ionization rates and observed NOx densities under consideration of the determined lifetimes of NOx, and calculate altitude dependent effective production rates of NOx due to ionization. For that we compare ionization rates of the AIMOS data base with the MIPAS measurements for the whole Austral polar summer 2003/04. We derive effective NOx-production rates to be applied to the AIMOS ionization rates which range from about 0.2 NOx-molecules per ion pair at 44 km to 0.9 NOx-molecules per ion pair at 54 km at a latitude of –63° S. At –73° S, the NOx-production rate ranges from about 0.2 NOx-molecules per ion pair at 44 km to 1.0 NOx-molecules per ion pair at 60 km. These effective production rates are considerably lower than predicted by box model simulations which could hint at an overestimation of the modeled ionization rates.