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–November 2003

Abstract

Abstract. We present altitude-dependent lifetimes of NOx, 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° S and 90° 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 NOx depletion by 0.1% at 44 km, increasing with altitude to 45% at 64 km. In addition, we show the correlation of modelled 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 from 15 October–31 December 2003. 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 0.7 NOx-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.

Local impact of solar variation on NO<sub>2</sub> in the lower mesosphere and upper stratosphere from 2007–2011

“…This is why the figure is shadowed at these altitudes. The NO 2 lifetimes are significantly lower at all altitudes than the NO x lifetimes after an SPE determined by Friederich et al (2013). τ is mostly triggered by dynamics at these altitudes (Brasseur and Solomon, 2005;Friederich et al, 2013).…”

Local impact of solar variation on NO<sub>2</sub> in the lower mesosphere and upper stratosphere from 2007 to 2012

“…Nevertheless, it should be considered that the NO 2 /NO x ratio decreases with increasing altitude at night. Additionally, the efficiency of NO x production due to ionization, which is mainly influenced by temperature-dependent reactions, shows its peak between 42 km and 52 km (Funke et al, 2011;Friederich et al, 2013). These two reasons could also explain the decrease in the production rate from 50 km to 52 km.…”

“…The NO 2 lifetimes are significantly lower at all altitudes than the NO x lifetimes after an SPE determined by Friederich et al (2013). τ is mostly triggered by dynamics at these altitudes (Brasseur and Solomon, 2005;Friederich et al, 2013). At an SPE, NO x is enhanced over the whole polar cap, whereas NO x enhancement due to electron precipitation is restricted to a small region.…”

“…This is why the figure is shadowed at these altitudes. The NO 2 lifetimes are significantly lower at all altitudes than the NO x lifetimes after an SPE determined by Friederich et al (2013). τ is mostly triggered by dynamics at these altitudes (Brasseur and Solomon, 2005;Friederich et al, 2013).…”

The Atmospheric Radiation Interaction Simulator (AtRIS): Description and Validation

“…The importance of energetic charged particle interaction with the Earth's atmosphere has been analyzed since the 1970s (see, e.g., Crutzen et al, 1975;Friederich et al, 2013;Jackman et al, 1980;Porter et al, 1976;Thorne, 1980;Warneck, 1972, and references therein). While strong solar energetic particle events can influence the ion chemistry in the upper atmosphere mainly above 40 km, the galactic cosmic ray contribution comes down to the stratosphere (see, e.g., Anet et al, 2013, and references therein).…”