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| Titel |
Mesosphere-to-stratosphere descent of odd nitrogen in February–March 2009 after sudden stratospheric warming |
| VerfasserIn |
S.-M. Salmi, P. T. Verronen, L. Thölix, E. Kyrölä, L. Backman, A. Yu. Karpechko, A. Seppälä |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 11, no. 10 ; Nr. 11, no. 10 (2011-05-18), S.4645-4655 |
| Datensatznummer |
250009744
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| Publikation (Nr.) |
 copernicus.org/acp-11-4645-2011.pdf |
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| Zusammenfassung |
| We use the 3-D FinROSE chemistry transport model (CTM) and Atmospheric
Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) observations to
study connections between atmospheric dynamics and middle atmospheric
NOx (NOx = NO + NO2) distribution. Two
cases are considered in the northern polar regions: (1) descent of
mesospheric NOx in February–March 2009 after a major sudden
stratospheric warming (SSW) and, for comparison, (2) early 2007 when no NOx
descent occurred. The model uses the European Centre for
Medium-Range Weather Forecasts (ECMWF) operational data for winds and
temperature, and we force NOx at the model upper altitude boundary
(80 km) with ACE-FTS observations. We then compare the model results
with ACE-FTS observations at lower altitudes. For the periods studied,
geomagnetic indices are low, which indicates absence of local NOx
production by particle precipitation. This gives us a good opportunity to
study effects of atmospheric transport on polar NOx. The model
results show no NOx descent in 2007, in agreement with ACE-FTS. In
contrast, a large amount of NOx descends in February–March 2009
from the upper to lower mesosphere at latitudes larger than 60° N, i.e. inside the polar vortex. Both observations and model
results suggest NOx increases of 150–200 ppb (i.e. by
factor of 50) at 65 km due to the descent. However, the model
underestimates the amount of NOx around 55 km by
40–60 ppb. According to the model results, chemical loss of
NOx is insignificant during the descent period, i.e. polar
NOx is mainly controlled by dynamics. The descent is terminated and
the polar NOx amounts return to pre-descent levels in mid-March, when
the polar vortex breaks. The break-up prevents the descending NOx
from reaching the upper stratosphere, where it could participate in catalytic
ozone destruction. Both ACE-FTS observations and FinROSE show a decrease of
ozone of 20–30 % at 30–50 km from mid-February to mid-March. In
the model, these ozone changes are not related to the descent but are due to
solar activation of halogen and NOx chemistry. |
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