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| Titel |
Unusual ionospheric effects observed during the intense 28 October 2003 solar flare in the Brazilian sector |
| VerfasserIn |
Y. Sahai, F. Becker-Guedes, P. R. Fagundes, W. L. C. Lima, A. J. Abreu, F. L. Guarnieri, C. M. N. Candido, V. G. Pillat |
| 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 ; 25, no. 12 ; Nr. 25, no. 12 (2008-01-02), S.2497-2502 |
| Datensatznummer |
250015956
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| Publikation (Nr.) |
 copernicus.org/angeo-25-2497-2007.pdf |
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| Zusammenfassung |
| The 28 October 2003 solar flare (X-ray Class X17.2) was one of the most
intense solar flares observed in the recent past. In the present
investigation we show the unusual ionospheric effects observed in the
Brazilian sector during this solar flare, using both the ionospheric
sounding observations obtained at the UNIVAP stations: Palmas (7–10.2° S,
48.2° W, dip lat. 5.5° S) and Sao Jose dos Campos (23.2° S,
45.9° W, dip lat. 17.6° S), Brazil; and ground-based global
positioning system (GPS) data obtained at the "Instituto Brasileiro de
Geografia e Estatística" (IBGE) stations: Imperatriz (5.5° S,
47.5° W, dip lat. 2.9° S), Brasilia (15.9° S, 47.9° W, dip
lat. 11.7° S), Presidente Prudente (22.3° S, 51.4° W, dip lat. 14.9° S),
and Porto Alegre (30.1° S, 51.1° W, dip lat. 20.7° S), Brazil; on two consecutive days, viz., 27 (without solar flare) and 28
(with solar flare) October 2003. It should be mentioned that the vertical
total electron content (VTEC) from the GPS observations obtained during the
solar flare showed an unusual simultaneous increase in the VTEC values at
about 11:00 UT at all four stations associated with the solar flare EUV
enhancements and lasted for about 3 h. However, no ionograms were
obtained at any of the two UNIVAP stations for a period of about 1 h
between about 11:00 to 12:00 UT. Before 11:00 UT (from about 10:45 UT) and
after 12:00 UT (to about 16:00 UT), the ionograms were only partial, with the low
frequency end missing. During this intense solar flare, hard X-rays (1 to 10
A), as observed by the GOES 12 satellite, were ejected by the Sun during a
long period (several hours), with peak radiation at about 11:10 UT. These
hard X-ray radiations can penetrate further into the ionosphere, causing
an increase in ionization in the lower part of ionosphere (D-region). In this
way, the lack of ionograms or partial ionograms, which indicates no echoes
or partial echoes of the transmitted digital ionosonde signals, are related
to intense absorption, resulting in complete or partial fade-out of radio
signals at the lower ionospheric heights. The partial and complete radio
fade-out observed in the Brazilian sector for more than six hours must have
resulted in considerable difficulties to the radio station operating
agencies using ionospheric radio transmissions. |
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