The South America VLF NETwork (SAVNET)

Raulin, J. P.; David, P. Correia de Matos; Hadano, Rubens; Saraiva, A. C. V.; Correia, E.; Kaufmann, P.

doi:10.1007/s11038-008-9269-4

Cited by 42 publications

(25 citation statements)

References 36 publications

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“…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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Section: Introductionmentioning

confidence: 99%

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

et al. 2010

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“…The South American VLF Network (SAVNET)) is a network of very low frequency (VLF) receivers in Brazil, Peru and Argentina [Raulin 2009]. The SAVNET VLF array tracks phase and amplitude of VLF waves which reflect in the D-region (~ 70 km), and the bottom E-region (~ 85-90 km), during daytime and night-time periods, respectively.…”

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Changes in animal activity prior to a major (M= 7) earthquake in the Peruvian Andes

Grant

Raulin

Freund

2015

Physics and Chemistry of the Earth, Parts A/B/C

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During earthquake preparation geophysical processes occur over varying temporal and spatial scales, some leaving their mark on the surface environment, on various biota, and even affecting the ionosphere. Reports on pre-seismic changes in animal behaviour have been greeted with scepticism by the scientific community due to the necessarily anecdotal nature of much of the evidence and a lack of consensus over possible causal mechanisms. Here we present records of changes in the abundance of mammals and birds obtained over a 30 day period by motiontriggered cameras at the Yanachaga National Park, Peru, prior to the 2011 magnitude 7.0 Contamana earthquake. In addition we report on ionospheric perturbations derived from nighttime very low frequency (VLF) phase data along a propagation paths passing over the epicentral region. Animal activity declined significantly over a 3-week period prior to the earthquake compared to periods of low seismic activity. Night-time ionospheric phase perturbations of the VLF signals above the epicentral area, fluctuating over the course of a few minutes, were observed, starting 2 weeks before the earthquake. The concurrent observation of two widely different and seemingly unconnected precursory phenomena is of interest because recently, it has been proposed that the multitude of reported pre-earthquake phenomena may arise from a single underlying physical process: the stress-activation of highly mobile electronic charge carriers in the Earth's crust and their flow to the Earth's surface. The flow of charge carriers through the Animal Activity prior to M=7 Earthquake in Peru Physics and Chemistry of the Earth 2 rock column constitutes and electric current, which is expected to fluctuate and thereby emit electromagnetic radiation in the ultralow frequency (ULF) regime. The arrival of the charge carriers can lead to air ionization at the ground-to-air interface and the injection of massive amounts of positive airborne ions, known to be aversive to animals.

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“…The South America VLF Network (SAVNET; Raulin et al, 2009) clearly showed sudden amplitude and phase changes at the corresponding times of eight of these X-ray bursts (Tanaka et al, 2010). Mondal et al (2012) found convincing evidence that the lower ionospheric height went down significantly by about 15 km during that event.…”

Section: Introductionmentioning

confidence: 95%

Ionospheric response to magnetar flare: signature of SGR J1550–5418 on coherent ionospheric Doppler radar

Mahrous

2017

Ann. Geophys.

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Abstract. This paper presents observational evidence of frequent ionospheric perturbations caused by the magnetar flare of the source SGR J1550-5418, which took place on 22 January 2009. These ionospheric perturbations are observed in the relative change of the total electron content ( TEC/ t) measurements from the coherent ionospheric Doppler radar (CIDR). The CIDR system makes high-precision measurements of the total electron content (TEC) change along raypaths from ground receivers to low Earth-orbiting (LEO) beacon spacecraft. These measurements can be integrated along the orbital track of the beacon satellite to construct the relative spatial, not temporal, TEC profiles that are useful for determining the large-scale plasma distribution. The observed spatial TEC changes reveal many interesting features of the magnetar signatures in the ionosphere. The onset phase of the magnetar flare was during the CIDR's nighttime satellite passage. The nighttime small-scale perturbations detected by CIDR, with TEC/ t ≥ 0.05 TECU s −1 , over the eastern Mediterranean on 22 January 2009 were synchronized with the onset phase of the magnetar flare and consistent with the emission of hundreds of bursts detected from the source. The maximum daytime large-scale perturbation measured by CIDR over northern Africa and the eastern Mediterranean was detected after ∼ 6 h from the main phase of the magnetar flare, with TEC/ t ≤ 0.10 TECU s −1 . These ionospheric perturbations resembled an unusual poleward traveling ionospheric disturbance (TID) caused by the extraterrestrial source. The TID's estimated virtual velocity is 385.8 m s −1 , with TEC/ t ≤ 0.10 TECU s −1 .

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The South America VLF NETwork (SAVNET)

Cited by 42 publications

References 36 publications

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

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

Changes in animal activity prior to a major (M= 7) earthquake in the Peruvian Andes

Ionospheric response to magnetar flare: signature of SGR J1550–5418 on coherent ionospheric Doppler radar

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