Abstract
Abstract. We use NO, NO2 and CO from MIPAS/ENVISAT to investigate the impact of energetic particle precipitation onto the NOx budget from the stratosphere to the lower mesosphere in the period from October 2003 to March 2004, a time of high solar and geomagnetic activity. We find that in the winter hemisphere the indirect effect of auroral electron precipitation due to downwelling of upper mesospheric/lower thermospheric air into the stratosphere prevails. Its effect exceeds even the direct impact of the very large solar proton event in October/November 2003 by nearly 1 order of magnitude. Correlations of NOx and CO show that the unprecedented high NOx values observed in the Northern Hemisphere lower mesosphere and upper stratosphere in late January and early February are fully consistent with transport from the upper mesosphere/lower thermosphere and subsequent mixing at lower altitudes. In the polar summer Southern Hemisphere, we observed an enhanced variability of NO and NO2 on days with enhanced geomagnetic activity, but this seems to indicate enhanced instrument noise rather than a direct increase due to electron precipitation. A direct effect of electron precipitation onto NOx can not be ruled out, but, if any, it is lower than 3 ppbv in the altitude range 40–56 km and lower than 6 ppbv in the altitude range 56–64 km. An additional significant source of NOx due to local production by precipitating electrons below 70 km exceeding several parts per billion as discussed in previous publications appears unlikely.
Highlights
Energetic particle precipitation has been acknowledged as a source of large disturbances to the chemical composition mainly of the polar middle atmosphere for several decades
During polar winter, NOx produced by energetic particle precipitation can be transported down from its source regions in the polar mesosphere or lower thermosphere into the polar stratosphere, where it will contribute to stratospheric ozone loss
The solar proton event on 30 October– 1 November 2003 is clearly visible as a strong increase of wndadrbdnysigMohfIt6Po5Ab◦Ss)e.irFf9nOnvr0eioagntt◦mtihulicNyoerlnO,edNasatcc.2oiyott.rAousntChbdlswleeeiOdirgrstneheab2roHsui0mmnt0megoaom3regnebiatnlsoosytephutthhMwairceendirdatle8aharbcytifdinhyrtaoauttM2nmdah0de-eIps0OPpno4bAcoiiungtliSotathnsbrotietnwnvohrloebety2hrrs0teelweea0ruxNti3vitshta(eouteitdornidqto.heuMtnehisbvrae.nairnpclAeHhofnlller2atomrg0lmae0vitso4oip4tmruiht0nedaexegtrtoehs-(eeqluatiivtaaaipuslblrdetoaeointtlutuborlteidnana1etideftorvuryorademdenenensgt4r.he(0BoaT–4nufh90tcmic0–esh◦ad7amgN0rsntioekgairvtmhtnuehdtdr,.abeAleodbdfaouNyveseOtboaxebvfdooaourlweut ent6hsw0ewekolimltnihnsiaegnltti1iontfudtdtahhyeee,ipsnNootOllhaaexrr (Butchart and Remsberg, 1986) polewards of 65◦)
Summary
Energetic particle precipitation has been acknowledged as a source of large disturbances to the chemical composition mainly of the polar middle atmosphere for several decades. Large NOx productions due to geomagnetic activity or relativistic electrons from the magnetosphere have been reported by Renard et al (2006) for January 2004 and by Clilverd et al (2009) for 11–15 February 2004 Evidence of a possible strong impact of relativistic electrons from the radiation belt on ozone in the middle stratosphere during mid-winter is reported by Sinnhuber et al (2006). We use observations of NO and NO2 from the MIPAS instrument onboard the ENVISAT satellite for the geomagnetically very active period from October 2003 to end of March 2004 to investigate the possible direct impact of energetic particle precipitation onto NOx in the middle atmosphere below 70 km.
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