Variability of NO<sub>x</sub> in the polar middle atmosphere from October 2003 to March 2004: vertical transport vs. local production by energetic particles
We use NO, NO<sub>2</sub> and CO from MIPAS/ENVISAT to investigate the impact of energetic particle precipitation onto the NO<sub>x</sub> budget from the stratosphere to the lower mesosphere in the period from October 2003 to March 2004, a time of high solar and geomagnetic a...
| Main Authors: | , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2014-07-01
|
| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/14/7681/2014/acp-14-7681-2014.pdf |
| Summary: | We use NO, NO<sub>2</sub> and CO from MIPAS/ENVISAT to investigate the impact of
energetic particle precipitation onto the NO<sub>x</sub> 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<sub>x</sub> and CO show that the unprecedented
high NO<sub>x</sub> 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 NO<sub>2</sub> 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<sub>x</sub> 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<sub>x</sub> due to local production by
precipitating electrons below 70 km exceeding several parts per billion as
discussed in previous publications appears unlikely. |
|---|---|
| ISSN: | 1680-7316 1680-7324 |