On the detectability of solar X-ray flares using very low frequency sudden phase anomalies
Tipo
Artigo
Data de publicação
2006
Periódico
Journal of Atmospheric and Solar-Terrestrial Physics
Citações (Scopus)
35
Autores
Raulin J.-P.
Abe Pacini A.
Kaufmann P.
Correia E.
Aparecida G. Martinez M.
Abe Pacini A.
Kaufmann P.
Correia E.
Aparecida G. Martinez M.
Orientador
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Título de Volume
Membros da banca
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Resumo
We have studied ionization excesses produced by enhancements of X-ray emission during solar flares using the very low frequency (VLF) response of the lower edge of the ionospheric D region. We focus on whether or not the X-rays associated with a given solar flare were responsible for a sudden phase anomaly (SPA) event, independently of the characteristics of the SPA. Approximately 1300 and 200 solar events were found to cause an ionospheric event, during periods of high and low solar activity, respectively. The main results of the present work are: (i) definite spectral characteristics are required for a solar flare to produce a measurable SPA; (ii) the probability of SPA occurrence due to faint solar flares, of X-ray class C1-C2 or lower, is higher during solar minimum; (iii) the same probability for more intense solar flares (class C3 or higher) does not depend on the solar activity conditions. Our observations suggest that the low ionosphere has different sensitivities depending on the solar activity, being more sensitive when the Sun is less active. These results also constitute an observational confirmation of recent findings showing that the ionospheric reference height is lower (by about {less-than or slanted equal to}1 km) during solar maximum. © 2005 Elsevier Ltd. All rights reserved.
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Assuntos Scopus
Solar activity cycle , Solar X-ray flares , Very low frequency propagation