Some relationships between solar X-ray bursts and SPA's produced on VLF propagation in the lower ionosphere

Kaufmann, P.; Barros, M. H. Paes de

doi:10.1007/bf02391673

Cited by 22 publications

(11 citation statements)

References 16 publications

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“…We shall assume that the X‐rays originated in the same H‐α flaring sites. Although the approximate correlation between the log of X‐rays fluxes and SPAs agree qualitatively with the earlier findings obtained for fewer VLF SPA events using the NRL Solrad Satellite [ Kaufmann and Paes de Barros , 1969; Muraoka et al , 1977], the present results for a bigger collection of events exhibit a much larger dispersion. X‐ray flares and SPAs follow the approximate relationship log( I ) = ∼ a (SPA) + b where the SPA is in deg/Mm and I in W/m 2 .…”

Section: Goes X Rays and Spassupporting

confidence: 89%

Solar flares not producing sudden phase advances

et al. 2002

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[1] We present a study of solar flares that do not produce disturbances in the low terrestrial ionosphere, detectable in very low frequency (VLF) low ionosphere propagation as sudden phase advances (SPA). We selected only flares with larger optical H-a importance (equal or larger than 1), occurred near the cycle 22 solar maximum (1987)(1988)(1989), at times when VLF data were available for long-distance propagation paths entirely illuminated by the Sun. For the 463 optical solar flares selected, we found that 18.8% had no measurable effects on the lower ionosphere. Inversely, all measured SPAs did have a solar counterpart, optical (such a subflare) and/or X-ray fluxes. Among the H-a flares that do not produce measurable disturbances in the low terrestrial ionosphere, there is a surprising selection for events occurred at the solar limbs. On the other hand, the X-ray flux for the H-a flares selected, obtained from GOES for the bands 0.5-4 Å and 1-8 Å exhibited a rather scattered correlation with the SPAs amplitudes. GOES X-rays fluxes for H-a flares not producing SPAs extend over 2-3 orders of magnitude. These results may suggest real physical distinctions between events. Possible explanations suggest the existence of a directional trend for the soft X-ray produced in flares possibly combined with the blockage of ionizing X rays behind the solar limbs.

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Section: Goes X Rays and Spassupporting

confidence: 89%

Solar flares not producing sudden phase advances

et al. 2002

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“…Most of the papers studying the relation between solar flares and the resulting response of the low ionosphere using the VLF technique deal with the correlation between the X‐ray peak power in a given photon energy range ( P x ) and the phase (ΔΦ) and/or amplitude (Δ A ) changes which are subsequently observed [ Kaufmann and Paes de Barros , 1969; Comarmond , 1977; Muraoka et al , 1977; Pant , 1993; Pant et al , 1983; Kaufmann et al , 2002; McRae and Thomson , 2004; Thomson et al , 2005; Pacini , 2006; Raulin et al , 2006; Zigman et al , 2007]. In general, the P x versus ΔΦ (or Δ A ) plots do present a good correlation for both variables, and it is possible to identify the faintest solar events detected by extrapolating the correlation toward these small events deducing a minimum soft X‐ray flux, P xm .…”

Section: Discussionmentioning

confidence: 99%

“…Departure from the above described quiescent situation occurs when there are ionization excesses in the low ionosphere. The reasons for that can be external sources of radiation like X‐ray solar flares [ Bracewell and Straker , 1949; Kaufmann and Paes de Barros , 1969; Muraoka et al , 1977], X‐ray bursts from remote objects like magnetar bursts [ Kaufmann et al , 1973; Rizzo Piazza et al , 1983; Tanaka et al , 2008; Raulin et al , 2009a], or meteor showers [ Chilton , 1961; Kaufmann et al , 1989]. The electrical properties of the EIW can also change due to perturbations from the inside of the waveguide like atmospheric lightning causing precipitation of initially trapped electrons [ Cummer , 1997], Transient Luminous Effects (TLEs) like red sprites and elves [ Inan et al , 1995; Pasko et al , 1995], and natural phenomena related to seismic‐electromagnetic effects [ Hayakawa et al , 1996].…”

Section: Introductionmentioning

confidence: 99%

Solar flare detection sensitivity using the South America VLF Network (SAVNET)

et al. 2010

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[1] We present recent observations of Sudden Phase Anomalies due to subionospheric propagation anomalies produced by solar X-ray flares. We use the new South America VLF Network (SAVNET) to study 471 ionospheric events produced by solar flares during the period May 2006 to July 2009 which corresponds to the present minimum of solar activity. For this activity level, we find that 100% of the solar flares with a X-ray peak flux above 5 × 10 −7 W/m 2 in the 0.1-0.8 nm wavelength range produce a significant ionospheric disturbance, while the minimum X-ray flux needed to do so is about 2.7 × 10 −7 W/m 2 . We find that this latter minimum threshold is dependent on the solar cycle, increasing when the Sun is more active, thus confirming that the low ionosphere is more sensitive during periods of low solar activity. Also, our findings are in agreement with the idea that the ionospheric D-region is formed and maintained by the solar Lyman-a radiation outside solar flare periods.

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“…The minimum X-ray power, Px, needed to produce a phase advance in the lower ionosphere can be estimated from previous works for different solar activity periods (Kaufmann and Paes de Barros, 1969;Comarmond, 1977;Pant et al, 1983;Pant, 1993; Kaufmann et al, 2002;McRae and Thomson, 2004;Thomson et al, 2005;Pacini, 2006;Zigman et al, 2007). The result is shown in Fig.…”

Section: Monitoring Of the Short-term Explosive Solar Radiationmentioning

confidence: 98%