Frequency Dependence of VLF Fading at Sunrise

Steele, F. K.; Crombie, D. D.

doi:10.1002/rds196726547

Cited by 17 publications

(7 citation statements)

References 4 publications

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“…A possible explanation, according to Walker, is the existence of some second mode in the light part of the path when this is small, thus affecting the time of occurrence of signal minima. A similar anomaly, becoming more severe at higher frequencies, was observed by Steele and Crombie (1967). Ries (1967) found that the first two phase steps at sunrise tended to split into substeps, with several small amplitude minima.…”

Section: Introductionsupporting

confidence: 67%

“…If the direct second mode signal were responsible for the anomalous signal minima, a greater variation with frequency would be expected. Steele and Crombie (1967) recorded the same transmissions from NPM and Haiku at Boulder, which is almost on the NPM-Washington great-circle path approximately 2.4 Mm from Washington. For the NPM-Boulder path, the night interference minima occur at the same value of DN, but the day interference pattern shifts towards the transmitter a distance of 2.4 Mm, a little more than one cycle of night interference.…”

Section: Npm-washingtonmentioning

confidence: 91%

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Identification of a New Type of Mode Conversion Interference in VLF Propagation

Kaiser

1968

Radio Science

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The sunrise and sunset interference patterns observed in VLF propagation over long paths are largely consistent with the model of mode conversion interference proposed h.y Crombie, which considers both the first and second modes in the nighttime portion of the path, hut only the first mode in the daytime portion. Several authors, however, have reported anomalies during the first part of the sunrise transition. Except for effects produced by a direct second mode, these anomalies may be explained by a model of mode conversion interference which involves first and second mode propagation along the daytime portion of the path, and first mode propagation along the nighttime portion.

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Section: Introductionsupporting

confidence: 67%

Section: Npm-washingtonmentioning

confidence: 91%

Identification of a New Type of Mode Conversion Interference in VLF Propagation

Kaiser

1968

Radio Science

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“…The distance D moved by the terminator along the propagation path between signal minima is a measure of the difference in phase velocity between the first and second modes [33] and is given by the simple relationship Values of D as a function of frequency have been made by many people with a considerable amount of agreement (e.g. [40] [41]). An example (Fig.23) provides evidence of higher values of D for propagation to the east relative to propagation to the west at middle latitudes [41].…”

Section: Terminator-generated Modal Interferencementioning

confidence: 99%

VLF Waveguide Propagation: The Basics

Lynn¹

2010

AIP Conference Proceedings

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In recent times, research has moved towards using VLF radio transmissions propagating in the earth-ionosphere waveguide as a detector of a variety of transient geophysical phenomena. A correct interpretation of such results depends critically on understanding the propagation characteristics of the path being monitored. The observed effects will vary depending on time of day, path length, path orientation, magnetic latitude and VLF frequency. This paper provides a brief tutorial of the relevant propagation dependencies for medium to long VLF paths best understood in terms of waveguide mode theory together with results either not previously published, not published in the open scientific literature or whose significance has been little recognised.

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“…Walker [1965] has reported the presence of anomalous TTs when the sunrise line was close to the receiver. In similar conditions, Steele and Crombie [1967] have reported abnormal TTs and emphasize a…”

Section: Resultsmentioning

confidence: 71%

“…Walker [] has reported the presence of anomalous TTs when the sunrise line was close to the receiver. In similar conditions, Steele and Crombie [] have reported abnormal TTs and emphasize a possible dependence with the VLF frequency. Lynn [] reported anomalous D distances recorded when the Terminator Line was within ± 20° latitude of the geomagnetic equator for an east‐to‐west oriented transequatorial VLF propagation path.…”

Section: Resultsmentioning

confidence: 99%

Estimating the VLF modal interference distance using the South America VLF Network (SAVNET)

Samanes¹,

Raulin

Macotela

et al. 2015

Radio Sci.

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Pronounced amplitude minima are observed during the subionospheric propagation of VLF waves at times (Terminator Times) when the Terminator Line crosses given locations along the propagation path. The distance between such two successive minima is called the modal interference distance D, which is related to nighttime mode propagation in the Earth-ionosphere waveguide. Therefore, the temporal behavior of the distance D can bring information on the dynamics of the nighttime lower ionosphere and on the presence of external forcing agents, including those associated with seismic activity. In this paper we present a methodology to estimate D based on the measure and analysis of the pronounced VLF amplitude minima. We have used a long-term database of almost 5 years from three different VLF propagation paths from the South America VLF Network. We emphasize that the accuracy of the determination of the distance D achieved by our method is better than those obtained in earlier studies. The reason for that is the use of a long-term continuous database, from different parallel propagation paths mainly oriented along the west-to-east direction. We discuss typical properties of the obtained distance D, as the simultaneous occurrence of amplitude minima for parallel propagation paths, anomalous values of D at locations where the Terminator Line is close to the receiver, and the derivation of the undisturbed nighttime ionospheric height at h N~8 8 km.

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Frequency Dependence of VLF Fading at Sunrise

Cited by 17 publications

References 4 publications

Identification of a New Type of Mode Conversion Interference in VLF Propagation

Identification of a New Type of Mode Conversion Interference in VLF Propagation

VLF Waveguide Propagation: The Basics

Estimating the VLF modal interference distance using the South America VLF Network (SAVNET)

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