%0 Journal Article
%@holdercode {isadg {BR SPINPE} ibi 8JMKD3MGPCW/3DT298S}
%@nexthigherunit 8JMKD3MGPCW/3ETR8EH
%@archivingpolicy denypublisher denyfinaldraft24
%@resumeid
%@resumeid
%@resumeid
%@resumeid 8JMKD3MGP5W/3C9JH2C
%@usergroup administrator
%@usergroup simone
%3 On the detectability of solar x ray.pdf
%B Journal of Atmospheric and Solar-Terrestrial Physics
%@dissemination WEBSCI; PORTALCAPES; AGU; MGA; COMPENDEX.
%D 2006
%2 sid.inpe.br/mtc-m16@80/2006/08.02.13.46.28
%4 sid.inpe.br/mtc-m16@80/2006/08.02.13.46
%X 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 C1C2 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 1 km) during solar maximum.
%8 June
%N 9
%T On the detectability of solar X-ray flares using very low frequency sudden phase anomalies
%@secondarytype PRE PI
%K Solar flares, X-rays, Ionosphere, Solar activity cycle, Very low frequency propagation.
%@group
%@group DAS-INPE-MCT-BR
%@group
%@group DAS-INPE-MCT-BR
%@secondarykey INPE-13938--PRE/9118
%@copyholder SID/SCD
%@issn 1364-6826
%@affiliation Centro de Rádio Astronomia e Astrofísica Mackenzie, Universidade Presbiteriana Mackenzie,
%@affiliation Instituto Nacional de Pesquisas Espaciais, Divisão de Astrofísica (INPE.DAS),
%@affiliation Centro de Rádio Astronomia e Astrofísica Mackenzie, Universidade Presbiteriana Mackenzie,
%@affiliation Instituto Nacional de Pesquisas Espaciais, Divisão de Astrofísica (INPE.DAS),
%@affiliation Programa de Pós-graduação em Engenharia Elétrica, Universidade Presbiteriana Mackenzie,
%P 1029-1035
%V 68
%A Raulin, Jean-Pierre,
%A Pacini, Alessandra Abe,
%A Kaufmann, Pierre,
%A Correia, Emília,
%A Martinez, Maria Aparecida G.,
%@area CEA