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| Titel |
Sudden post-midnight decrease in equatorial F-region electron densities associated with severe magnetic storms |
| VerfasserIn |
D. R. Lakshmi, B. Veenadhari, R. S. Dabas, B. M. Reddy |
| 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 ; 15, no. 3 ; Nr. 15, no. 3, S.306-313 |
| Datensatznummer |
250012667
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| Publikation (Nr.) |
 copernicus.org/angeo-15-306-1997.pdf |
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| Zusammenfassung |
| A detailed analysis of the responses of the
equatorial ionosphere to a large number of severe magnetic storms shows the
rapid and remarkable collapse of F-region ionisation during post-midnight hours;
this is at variance with the presently accepted general behaviour of the
low-latitude ionosphere during magnetic storms. This paper discusses such
responses as seen in the ionosonde data at Kodaikanal (Geomagn. Lat. 0.6 N). It
is also observed that during magnetic storm periods the usual increase seen in
the h'F at Kodaikanal during sunset hours is considerably suppressed and these
periods are also characterised by increased foF2 values. It is suggested that
the primary process responsible for these dramatic pre- and post-midnight
changes in foF2 during magnetic storms could be due to changes in the magnitude
as well as in the direction of usual equatorial electric fields. During the
post-midnight periods the change in electric-field direction from westward to
eastward for a short period causes an upward E × B
plasma drift resulting in increased h'F and decreased electron densities in the
equatorial region. In addition, it is also suggested that the enhanced
storm-induced meridional winds in the thermosphere, from the poles towards the
equator, may also cause the decreases in electron density seen during
post-midnight hours by spatially transporting the F-region ionisation southwards
away from Kodaikanal. The paper also includes a discussion on the effects of
such decreases in ionisation on low-latitude HF communications. |
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