A synoptic study of VLF sudden phase anomalies recorded at Visakhapatnam

Khan, Ibrahim; Devi, M.; Arunamani, T.; Rao, D. Narayana

doi:10.1186/bf03351886

Cited by 7 publications

(11 citation statements)

References 10 publications

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“…Wait (1959) and several authors made use of it, e.g. Kamada (1985), Khan et al (2005). For a waveguide in 1st mode approximation, for small λ/ h and small h he found a relation for the relative phase velocity decrease with decreasing reflection height from which, because of…”

Section: Propagation Calculations and Modeling Resultsmentioning

confidence: 99%

Modeling solar flare induced lower ionosphere changes using VLF/LF transmitter amplitude and phase observations at a midlatitude site

Schmitter¹

2013

Ann. Geophys.

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Remote sensing of the ionosphere bottom using long wave radio signal propagation is a still going strong and inexpensive method for continuous monitoring purposes. We present a propagation model describing the time development of solar flare effects. Based on monitored amplitude and phase data from VLF/LF transmitters gained at a mid-latitude site during the currently increasing solar cycle no. 24 a parameterized electron density profile is calculated as a function of time and fed into propagation calculations using the LWPC (Long Wave Propagation Capability). The model allows to include lower ionosphere recombination and attachment coefficients, as well as to identify the relevant forcing X-ray wavelength band, and is intended to be a small step forward to a better understanding of the solar–lower ionosphere interaction mechanisms within a consistent framework

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Section: Propagation Calculations and Modeling Resultsmentioning

confidence: 99%

Modeling solar flare induced lower ionosphere changes using VLF/LF transmitter amplitude and phase observations at a midlatitude site

Schmitter¹

2013

Ann. Geophys.

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“…However, most of the reports on extraterrestrial radiation effect on the ionospheric D-region are originated in solar flares. During these flares, X-ray flux received at the Earth strongly intensifies within a few minutes and decays in up to several hours, while strongly affecting ionization processes in the ionosphere [e.g., Mitra and Rowe, 1972;Hunsucker and Hargreaves, 2002;Khan et al, 2005;Clilverd et al, 2009].…”

Section: Space Weather Phenomena and Eclipsesmentioning

confidence: 99%

“…Nevertheless, several studies were made in order to find X-ray flux thresholds needed for the generation of a VLF NB SPA [e.g., Kaufmann and de Barros, 1969;Muraoka et al, 1977;Pant, 1993;Khan et al, 2005]. Similarly, Kaufmann et al [2002] studied numerous solar flare events that did not produce SPAs.…”

Section: Space Weather Phenomena and Eclipsesmentioning

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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“…The majority of these studies reported the correlation between the logarithmic of the solar X‐ray peak flux (W/m 2 ) of the flare and the subsequent ionospheric disturbance observed as VLF anomalies. From this correlation it is possible to estimate the smallest solar X‐ray flare event that disturbed the daytime lower ionosphere conductivity enough to perturb the propagation of VLF waves (Kaufmann & Paes de Barros, ; Khan et al, ; Muraoka et al, ; Pant, ; Raulin et al, ). This minimal detected event suggests how sensitive the lower ionosphere is to solar flares; however, more understanding on this notion is needed.…”

Section: Introductionmentioning

confidence: 99%

Lower Ionosphere Sensitivity to Solar X‐ray Flares Over a Complete Solar Cycle Evaluated From VLF Signal Measurements

et al. 2017

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The daytime lower ionosphere behaves as a solar X‐ray flare detector, which can be monitored using very low frequency (VLF) radio waves that propagate inside the Earth‐ionosphere waveguide. In this paper, we infer the lower ionosphere sensitivity variation over a complete solar cycle by using the minimum X‐ray fluence (FXmin) necessary to produce a disturbance of the quiescent ionospheric conductivity. FXmin is the photon energy flux integrated over the time interval from the start of a solar X‐ray flare to the beginning of the ionospheric disturbance recorded as amplitude deviation of the VLF signal. FXmin is computed for ionospheric disturbances that occurred in the time interval of December–January from 2007 to 2016 (solar cycle 24). The computation of FXmin uses the X‐ray flux in the wavelength band below 0.2 nm and the amplitude of VLF signals transmitted from France (HWU), Turkey (TBB), and U.S. (NAA), which were recorded in Brazil, Finland, and Peru. The main result of this study is that the long‐term variation of FXmin is correlated with the level of solar activity, having FXmin values in the range (1 − 12) × 10−7 J/m2. Our result suggests that FXmin is anticorrelated with the lower ionosphere sensitivity, confirming that the long‐term variation of the ionospheric sensitivity is anticorrelated with the level of solar activity. This result is important to identify the minimum X‐ray fluence that an external source of ionization must overcome in order to produce a measurable ionospheric disturbance during daytime.

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A synoptic study of VLF sudden phase anomalies recorded at Visakhapatnam

Cited by 7 publications

References 10 publications

Modeling solar flare induced lower ionosphere changes using VLF/LF transmitter amplitude and phase observations at a midlatitude site

Modeling solar flare induced lower ionosphere changes using VLF/LF transmitter amplitude and phase observations at a midlatitude site

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

Lower Ionosphere Sensitivity to Solar X‐ray Flares Over a Complete Solar Cycle Evaluated From VLF Signal Measurements

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