Solar–terrestrial, ionospheric and natural phenomena studies using the South America VLF network (SAVNET)

Raulin, J. P.; Bertoni, F.; Kaufmann, P.; Gavilán, Hernan R.; Correia, E.; Hadano, Rubens; Schuch, Nelson Jorge

doi:10.1016/j.jastp.2010.11.029

Cited by 5 publications

(6 citation statements)

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“…The general pattern of the VLF narrowband phase effect associated with the appearance of the C region as observed by our measurements is well fitted by a function of the solar mean zenith angle (sec χ m ) daily variation for the path considered [ Raulin et al ., , ; Gavilán et al ., 2009]. χ m is the mean zenith angle calculated by utilizing 100 discrete values of χ i along a given VLF path at a determined time of day.…”

Section: Discussionmentioning

confidence: 99%

“…We have applied the same methodology used by Raulin et al . [, ] and Gavilán et al . [] and performed the analysis of the C region phase effect parameter, ∆, defined as the difference of phase (φ) measured at the points A and B (as seen in the details of Figure ):

Δ = {normalφ}_{normalA} - {normalφ}_{normalB} (degrees)

where φ A corresponds to the daily maximum produced by the presence of the C region and φ B corresponds to the point when the C region effect ends and starts to show the presence of the D region.…”

Section: Instrumentationmentioning

confidence: 99%

“…[13] We have applied the same methodology used by Raulin et al [2010Raulin et al [ , 2011 and Gavilán et al [2009] and performed the analysis of the C region phase effect parameter, Δ, defined as the difference of phase (ϕ) measured at the points A and B (as seen in the details of Figure 2):…”

Section: Instrumentationmentioning

confidence: 99%

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Lower ionosphere monitoring by the South America VLF Network (SAVNET): C region occurrence and atmospheric temperature variability

et al. 2013

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[1] Daily profiles of phase measurements as observed on fixed VLF paths generally show a transient phase advance, followed by a phase delay, for about 90 min after sunrise hours. This is indicative of a reflecting ionospheric C region developing along the terminator line at an altitude below the normal D region. The suggested occurrence of a C region is consistent with rocket measurements made in the 1960s, showing a maximum of the electron density between 64 and 68 km, and by radio sounding in the 1980s. In order to correctly describe the properties of the phase effect associated with the presence of a C region, it is important to understand the subionospheric propagation characteristics of the VLF paths. In this paper, we analyze the variations presented by the temporal properties of the VLF narrowband phase effect and determined a parameter associated with the appearance of the C region at sunrise hours observed by receivers from the South America VLF Network. Periodic patterns emerge from the parameter curves. Two distinct temporal behavior regimes can be identified: one exhibiting slow variations between March and October, and another one exhibiting faster variations between October and March. Solar illumination conditions and the geometrical configuration of the VLF paths relative to the sunrise terminator partly explain the slow variation regime. During periods of faster variations, we have observed good association with atmospheric temperature variability found in the measurements of the Thermosphere Ionosphere Mesosphere Energetics and Dynamics and Sounding of the Atmosphere using Broadband Emission Radiometry satellite instrument, which we assume to be related to the winter anomaly atmospheric phenomenon. However, when comparing the parameter time series with temperature curves, no direct one-to-one correspondence was found for transient events.Citation: Bertoni, F. C. P., J.-P. Raulin, H. R. Gavila´n, P. Kaufmann, R. Rodriguez, M. Clilverd, J. S. Cardenas, and G. Fernandez (2013), Lower ionosphere monitoring by the South America VLF Network (SAVNET): C region occurrence and atmospheric temperature variability,

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Section: Discussionmentioning

confidence: 99%

Δ = {normalφ}_{normalA} - {normalφ}_{normalB} (degrees)

Section: Instrumentationmentioning

confidence: 99%

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Lower ionosphere monitoring by the South America VLF Network (SAVNET): C region occurrence and atmospheric temperature variability

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“…They assumed that the greater attenuation rate during solar minimum arises from the combination of smaller solar Lyman-α flux and higher cosmic ray intensity, resulting in smaller electron density profile slope at the bottom of the D-region, followed by a stronger attenuation of VLF signals. In addition to monitoring the solar cycle during midday, Raulin et al [2011] have demonstrated that the solar cycle can also be examined in phase effect measurements of the C-region, a transient reflecting layer located at an altitude range of ~63-69 km [e.g., Sechrist, 1968;Rasmussen et al, 1980], which develops during sunrise, and produces a phase delay in VLF NB data for ~1-2 hours [Kuntz et al, 1991;Bertoni et al, 2013].…”

Section: Long-term Oscillations and Trendsmentioning

confidence: 99%

On the Use of VLF Narrowband Measurements to Study the Lower Ionosphere and the Mesosphere–Lower Thermosphere

Silber

Price

2016

Surv Geophys

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The ionospheric D-region (~60 km up to ~95 km) and the corresponding neutral atmosphere, often refered to as the mesosphere-lower-thermosphere (MLT) are challenging and costly to probe in-situ. Therefore, remote sensing techniques have been developed over the years. One of these is based on VLF (Very low frequency, 3-30 kHz) electromagnetic waves generated by various natural and manmade sources. VLF waves propagate within the Earth-ionosphere waveguide, and are extremely sensitive to perturbations occurring in the D-region along their propagation path. Therefore, measurements of these signals serve as an inexpensive remote sensing technique for probing the lower ionosphere and the MLT region. This paper reviews the use of VLF narrowband (NB) signals (generated by man-made transmitters) in the study of the D-region and the MLT for over 90 years. The fields of research span time scales from microseconds to decadal variability, and incorporate lightning-induced short term perturbations; extraterrestrial radiation bursts; energetic particle precipitation events; solar eclipses; lower atmospheric waves penetrating into the D-region; sudden stratospheric warming events; the annual oscillation; the solar cycle; and finally, the potential use of VLF NB measurements as an anthropogenic climate change monitoring technique.

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“…On longer timescales, the variability of the quiescent Lyman‐α emission between solar minimum and maximum has been proposed to account for the differences of the observed ionospheric response to solar flares [ Pacini , ; Pacini and Raulin , ]. The same Lyman‐α variability was also found to be responsible for the long‐term changes of the properties of the ionospheric C region [ Raulin et al ., ].…”

Section: Introductionmentioning

confidence: 99%

Response of the low ionosphere to X‐ray and Lyman‐α solar flare emissions

et al. 2013

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Using soft X‐ray measurements from detectors onboard the Geostationary Operational Environmental Satellite (GOES) and simultaneous high‐cadence Lyman‐α observations from the Large Yield Radiometer (LYRA) onboard the Project for On‐Board Autonomy 2 (PROBA2) ESA spacecraft, we study the response of the lower part of the ionosphere, the D region, to seven moderate to medium‐size solar flares that occurred in February and March of 2010. The ionospheric disturbances are analyzed by monitoring the resulting sub‐ionospheric wave propagation anomalies detected by the South America Very Low Frequency (VLF) Network (SAVNET). We find that the ionospheric disturbances, which are characterized by changes of the VLF wave phase, do not depend on the presence of Lyman‐α radiation excesses during the flares. Indeed, Lyman‐α excesses associated with flares do not produce measurable phase changes. Our results are in agreement with what is expected in terms of forcing of the lower ionosphere by quiescent Lyman‐α emission along the solar activity cycle. Therefore, while phase changes using the VLF technique may be a good indicator of quiescent Lyman‐α variations along the solar cycle, they cannot be used to scale explosive Lyman‐α emission during flares.

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Solar–terrestrial, ionospheric and natural phenomena studies using the South America VLF network (SAVNET)

Cited by 5 publications

References 38 publications

Lower ionosphere monitoring by the South America VLF Network (SAVNET): C region occurrence and atmospheric temperature variability

Lower ionosphere monitoring by the South America VLF Network (SAVNET): C region occurrence and atmospheric temperature variability

On the Use of VLF Narrowband Measurements to Study the Lower Ionosphere and the Mesosphere–Lower Thermosphere

Response of the low ionosphere to X‐ray and Lyman‐α solar flare emissions

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