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| Titel |
Observations of nitric oxide in the Antarctic middle atmosphere during recurrent geomagnetic storms |
| VerfasserIn |
D. A. Newnham, P. J. Espy, M. A. Clilverd, C. J. Rodger, A. Seppälä, D. J. Maxfield, P. Hartogh, K. Holmén, R. B. Horne |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250063344
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| Zusammenfassung |
| The odd nitrogen (NOx) species nitric oxide (NO) and nitrogen dioxide (NO2) are produced
in the middle atmosphere by precipitating energetic electrons and protons. In the
thermosphere and upper mesosphere NOx exists mainly as NO but below 70 km
conversion to NO2 occurs. In darkness NOx has a sufficiently long lifetime to be
transported downward by the polar vortex at high latitudes during winter and impact on
ozone abundances. NOx may be produced more frequently and persistently by
energetic electron precipitation from the Earth’s magnetosphere than by solar protons.
However, it is unclear which electron energies are most important for stratospheric
chemistry. Electrons in the range 10 keV to several MeV precipitate from the radiation
belts in the subauroral zone at geomagnetic latitudes -¤ 75Ë , and particularly in
the southern hemisphere and pole-ward of the South-Atlantic Magnetic Anomaly
(SMA). Although in general the precipitating flux decreases rapidly with increasing
electron energy this mechanism can produce NOx directly in the stratosphere and
mesosphere.
To establish high-latitude NOx production throughout the polar night, follow its transport,
and determine its effects on the composition and chemistry of the mesosphere and
stratosphere we have developed and deployed a 230-250 GHz passive microwave radiometer
in Antarctica to observe NO, ozone (O3), and carbon monoxide (CO). Here we report
ground-based measurements made from Troll station (72Ë 01’S 02Ë 32’E, geomagnetic
latitude 65Ë ), a location equator-ward of the auroral zone, pole-ward of the area of radiation
belt precipitation and the SMA, and deep within the polar vortex during the Austral
winter.
Our observations show enhanced mesospheric NO volume mixing ratio (VMR) reaching
1.2 ppmv at 65–80 km during a series of small recurrent geomagnetic storms in the 2008
polar autumn and winter. The Lomb normalized periodogram of the NO VMR time series
averaged over 65-80 km for days 80 to 220 of 2008 (20 March to 7 August) shows a peak
exceeding the 95% confidence limit at 27 days, matching the solar rotation period. For 2008
days 80 to 129 the radiometer NO VMR data is moderately correlated (r = 0.67, lag time
of 0.9 days) with 90Ë telescope “trapped” electron count rate for the >300 keV
channel of the SEM-2 MEPED instrument onboard the low altitude (300 keV electron count rate and a
longer lag time of 4-5 days. The altitude profile of mesospheric NO, and ionisation
data for the lower ionosphere from 30 MHz and 51.4 MHz widebeam riometers at
SANAE IV station (71Ë 40’S, 02Ë 51’W) and the AARDVARK (Antarctic-Arctic
Radiation-belt (Dynamic) Deposition - VLF Atmospheric Research Konsortium) network,
suggests mesospheric NO is produced by ~100-300 keV electron precipitation with
significant downwards transport in the southern-hemisphere winter-time polar vortex. |
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