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| Titel |
Twilight anomaly, midday recovery and cutoff latitudes during the intense polar cap absorption event of March 1991 |
| VerfasserIn |
H. Ranta, H. Yamagishi, P. Stauning |
| 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 ; 13, no. 3 ; Nr. 13, no. 3, S.262-276 |
| Datensatznummer |
250011786
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| Publikation (Nr.) |
 copernicus.org/angeo-13-262-1995.pdf |
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| Zusammenfassung |
| A study was made of the polar cap absorption
(PCA) event on 23-24 March 1991 produced by the largest solar proton event at
E>10 MeV since August 1972. This PCA event was related to a solar flare in
the eastern hemisphere lasting only 2 days and exhibiting a long time delay
between the flare and the increase of ionospheric absorption. Midday recovery
occurred regularly each PCA day near the cut-off latitudes during the noontime
hours and is attributed to the daily variation in the proton cut-off latitudes.
The maximum absorption during the PCA event was observed at high latitudes or
near the cut-off latitudes where ionization may be due to both solar protons and
trapped particles. The minimum in the absorption values during the night-time
hours would appear to be caused by the chemistry of the D-region as well as
access of the solar protons into the polar cap area. |
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