Index Geophysics

Variability of NOx in the polar middle atmosphere from October 2003 to March 2004: vertical transport vs. local production by energetic particles

We use NO, NO₂ and CO from MIPAS/ENVISAT to investigate the impact of energetic particle precipitation onto the NO_x 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 NO_x and CO show that the unprecedented high NO_x 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 NO_x 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 NO_x due to local production by precipitating electrons below 70 km exceeding several parts per billion as discussed in previous publications appears unlikely.

Sinnhuber, M.

Funke, B.

von Clarmann, T.

Lopez-Puertas, M.

Stiller, G. P.

Seppälä, A.

2018-09-13

Text

application/pdf

10.5194/acp-14-7681-2014

https://acp.copernicus.org/articles/14/7681/2014/

eISSN: 1680-7324

eng