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| Titel |
Physical mechanism of strong negative storm effects in the daytime ionospheric F2 region observed with EISCAT |
| VerfasserIn |
A. Mikhailov, K. Schlegel |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 16, no. 5 ; Nr. 16, no. 5, S.602-608 |
| Datensatznummer |
250013280
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| Publikation (Nr.) |
 copernicus.org/angeo-16-602-1998.pdf |
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| Zusammenfassung |
A self-consistent method for daytime F-region
modelling was applied to EISCAT observations during two periods comprising the
very disturbed days 3 April 1992 and 10 April 1990. The observed strong Ne
decrease at F2-layer heights originated from different physical mechanisms in
the two cases. The negative F2-layer storm effect with an NmF2
decrease by a factor of 6.4 on 3 April 1992 was produced by enhanced electric
fields (E≈85 mV/m) and strong downward plasma drifts,
but without any noticeable changes in thermospheric parameters. The increase of
the O+ + N2 reaction rate resulted in a strong enrichment
of the ionosphere with molecular ions even at F2-layer heights. The enhanced
electric field produced a wide mid-latitude daytime trough on 03 April 1992 not
usually observed during similar polarization jet events. The other strong
negative storm effect on 10 April 1990 with a complete disappearance of the
F2-layer maximum at the usual heights was attributed mainly to changes in
neutral composition and temperature. A small value for the shape parameter S
in the neutral temperature profile and a low neutral temperature at 120 km
indicate strong cooling of the lower thermosphere. We propose that this cooling
is due to increased nitric oxide concentration usually observed at these heights
during geomagnetic storms.
Key words. Atmospheric composition and structure ·
Thermosphere · Ionosphere · Ion chemistry and composition · Atmosphere
interactions |
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