VLF Propagation Effects produced by the Eclipse

Schaal, Ricardo Ernesto; Mendes, Aracy M.; Ananthakrishnan, S.; Kaufmann, P.

doi:10.1038/2261127a0

Cited by 11 publications

(3 citation statements)

References 2 publications

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“…A larger number of papers have looked at VLF/LF beacons as a method to infer ionospheric changes. Kaufmann and Schaal () and Schaal et al () presented VLF observations of the 12 November 1966 eclipse over South America, finding that the NPM transmitter (then at 26.1 kHz) from Hawaii was delayed by 10 μs (or 94°). Hoy () noted VLF phase delays of ∼3.3 μs (19°) during 22 September 1968 eclipse over Asia, on an extremely long 17‐Mm path from Rugby, UK, to Canberra, Australia, at 16 kHz.…”

Section: Introductionmentioning

confidence: 99%

The Lower Ionospheric VLF/LF Response to the 2017 Great American Solar Eclipse Observed Across the Continent

Cohen

Gross

Higginson‐Rollins

et al. 2018

Geophysical Research Letters

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We present observations from 11 very low frequency (VLF)/low‐frequency (LF) receivers across the continental United States during the 21 August 2017 “Great American Solar Eclipse.” All receivers detected transmissions from VLF/LF beacons below 50 kHz, while seven also recorded LF beacons above 50 kHz, yielding dozens of individual transmitter‐receiver radio links. Our observations show two separable superimposed signatures: (1) a gradual rise and fall in signal levels visible on almost all paths as the eclipse advances and then declines, as VLF attenuation is reduced by the changing ionosphere under an eclipsed Sun, and (2) direct reflective scattering off the narrow 100‐km‐wide totality spot, observed more uniquely when the transmitter or receiver, if not both, are relatively close to the totality spot.

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Section: Introductionmentioning

confidence: 99%

The Lower Ionospheric VLF/LF Response to the 2017 Great American Solar Eclipse Observed Across the Continent

Cohen

Gross

Higginson‐Rollins

et al. 2018

Geophysical Research Letters

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“…With wavelengths of tens of kilometers, VLF waves bounce within the Earth and ionosphere (EI) waveguide and can propagate for long distances with relatively low attenuation. Abnormal changes in VLF signals, especially those from navy transmitters, are usually caused by the electron density disturbance in the D-region ionosphere [4], which, in most cases, is due to intense space weather events, for example, solar eclipses [26].…”

Section: Introductionmentioning

confidence: 99%

A Comparative Study of VLF Transmitter Signal Measurements and Simulations during Two Solar Eclipse Events

Cheng

et al. 2023

Remote Sensing

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To monitor the Very-Low-Frequency (VLF) environment, a VLF detection system has been installed in Suizhou, China, a location with the longitude almost identical to that of the NWC transmitter in Australia. In the years 2019 and 2020, two solar eclipses crossed the NWC–Suizhou path at different locations. Each solar eclipse event represents a naturally occurring controlled experiment, but these two events are unique in that similar levels of electron density variation occurred at different locations along the VLF propagation path. Therefore, we conducted a comparative study using the VLF measurements during these two eclipses. Previous studies mostly estimated a pair of the reflection height (h′) and sharpness parameter (β) using the Long Wavelength Propagation Capability code, whereas, in this study, we use the VLF amplitude and phase as constraints in order to find the electron density change that best explains the VLF measurements. The eclipse measurements could be best explained if the path-averaged β value was 0.56 and 0.62 km−1 for the 2019 and 2020 eclipse, respectively. The VLF reflection height increased from 71.5 to 73.3 km for the 2019 eclipse and from 71.1 to 72.8 km for the 2020 eclipse. The best-fit β values were consistent with the Faraday International Reference Ionosphere model and statistical studies, and the h′ change was also consistent with previous studies and theoretical calculations. Moreover, present results suggested that VLF signals collected by a single receiver were not sensitive to where the electron density change occurs along the propagation path but reflected the average path condition. Therefore, a network of VLF receivers is required in order to monitor in real time the spatial extent of the space weather events that disturb the lower ionosphere.

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“…Because VLF waves do not reflect from any specific electron density, particularly for near-vertical incidence, and are affected by the geomagnetic field, conclusions about aeronomy based on such assumptions are questionable. Long-path VLF measurements during eclipses [Sears, 1965;Kaufman and Schaal, 1968;Hoy, 1969;Schaal et al, 1970] have not provided much more information than magnitudes of phase and amplitude changes and the time of their maximum excursion relative to the time of the eclipse maximum along the VLF path.…”

Section: Introductionmentioning

confidence: 99%

Observed and Predicted VLF Phase Behavior for the Solar Eclipses of September 11, 1969, and March 7, 1970

Noonkester¹,

Sailors²

1971

Radio Science

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A VLF propagation and a D‐region aeronomy model have been used to predict the effect of two solar eclipses on VLF propagation to Aztec, Arizona. Transmissions at 12.2 kHz from Hawaii were monitored during the eclipse on September 11, 1969; and transmissions at 12.0 kHz from Trinidad, at 24 kHz from transmitter NBA, at 12.5 kHz from Forestport, New York, and at 17.8 kHz from transmitter NAA were monitored during the eclipse on March 7, 1970. The VLF phase predictions were found to agree with measurements except for the two nearly coincident northerly paths from Forestport and NAA.

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VLF Propagation Effects produced by the Eclipse

Cited by 11 publications

References 2 publications

The Lower Ionospheric VLF/LF Response to the 2017 Great American Solar Eclipse Observed Across the Continent

The Lower Ionospheric VLF/LF Response to the 2017 Great American Solar Eclipse Observed Across the Continent

A Comparative Study of VLF Transmitter Signal Measurements and Simulations during Two Solar Eclipse Events

Observed and Predicted VLF Phase Behavior for the Solar Eclipses of September 11, 1969, and March 7, 1970

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