A theoretical model for equatorial ionospheric spread-F echoes in the HF and VHF bands

Booker, Henry G.; Ferguson, J. A.

doi:10.1016/0021-9169(78)90032-6

Cited by 31 publications

(15 citation statements)

References 146 publications

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“…There is also a theoretical study [Booker and Fergusen, 1978] connecting TIDs and spread F. As mentioned above, at least part of the spread F development sequence that we are proposing (the bottomside bulges) seems to have a TID connection. Also, we can often see discrete traces embedded in the diffuse "cloud" of spread F echoes.…”

Section: A Canadian Advancedmentioning

confidence: 63%

Presunrise spread F at Fortaleza

MacDougall¹,

Abdu²,

Jayachandran³

et al. 1998

J. Geophys. Res.

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Abstract. At Fortaleza, Brazil, in the equatorial zone about 400 km south of the magnetic equator a presunrise (secondary) maximum of spread F occurrence is observed during sunspot minimum and, in particular, during December solstice. The spread F takes the form of patches of irregularities that are convecting eastwards at-50 rn s '• . Most of the patches are collocated with bottomside bulges of the ionosphere. Our measurements indicate that these bottomside bulges are unstable due to a gradient-drift instability that is slowly growing and produces the spread F. The bulges themselves seem to be evidence of a Rayleigh-Taylor instability process.

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Section: A Canadian Advancedmentioning

confidence: 63%

Presunrise spread F at Fortaleza

MacDougall¹,

Abdu²,

Jayachandran³

et al. 1998

J. Geophys. Res.

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“…At the small scale (large wave number) end, the "inner scale" is thought to lie at approximately the ion gyroradius ("-3 m) (Booker, Ferguson, 1978;Woodman, Basu, 1978).…”

Section: Spectral Properties Of Irregularitiesmentioning

confidence: 99%

Effects of Strong Scattering on Transionospheric Propagation

Sprague¹

1989

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A JAN12 1990Appro~d for pUbic releas; Cstrbtln is wianited. Approved for public release; distribution is unlimited. 01 12 072 NAVAL OCEAN SYSTEMS CENTER ABSTRACT PWl&mn 200 w ds). .This report presents preliminary results of an effort to model the effects of ionospheric electron density irregularities on transionospheric propagation. The focus of the report is on propagation at HF and low VHF, where strong multiple scattering is often encountered. A strong scattering model is therefore used to predict the effects on such parameters as the phase autocorrelation function, the spectrum of intensity fluctuations, and the fluctuation in angle of arrival. Reqrements for improvements in the model and directions for later work are discussed. PREFACEThis report presents the results of modeling the effects of electron density irregularities on transionospheric propagation. The objective of this effort has been to provide a tool for determining, in real time, the expected effects of such irregularities on the performance of a given transionospheric monitoring system. While these effects can take several forms, we concentrate here on the -ariation in the phase of the signal due to scattering caused by such irregularities.In this report, we shall be mainly interested in remote locating systems. Such systems rely on accurate measurements of the phase difference between separated receive antennas to provide estimates of apparent angular location (azimuth/ elevation). Fluctuations in this phase difference due to scattering caused by electron density irregularities result in a consequent fluctuation in the apparent location of the transmitter. System performance can be seriously degraded if the correlation in the phase fluctuation between antennas is low or the mean square fluctuation in phase is large. In any case, the accurate determination of the phase fluctuations provides an estimate of the error for a given location estimate and thus provides important information for the system user.Another feature that must be addressed under strong multiple-scattering conditions is the reduction of correlation in the intensity of the signal. Under such scattering conditions, defocusing by large scale* irregularities can cause deep small-period fades in signal strength. For sufficiently strong scattering, these signal fades may have a spatial extent on the order of the size of the locating system (tens of meters). This loss of signal makes the system unreliable at best and, in some cases, inoperable.This area of investigation is not completely new; there exists a large body of related work. What is different about this effort is the extension to low VHF and HF operational frequencies. Previous work has, for the most part, dealt with higher frequencies where, in general, the relatively simple single-scatter models are applicable. Also, at these frequencies, one can generally ignore the refractive effects of the background ionization. This simplifies the implementation of the models considerably.At lower frequencies, strong multiple refra...

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“…A recurring question remains to be the one concerning the bandwidth of the irregularity structures required for interpreting the ionogram spread F traces, which inevitably should invoke mechanisms for radio signal returns from the irregularities. The considered mechanisms include total reflection from over dense structures (e.g., [1,2,3] ), and references therein) (See also, [4] ) to partial reflection or Rayleigh scattering from small irregularities [5,6] and to Bragg backscattering (or coherent scattering) by plasma density fluctuations with scale size of λ/2, λ being the radio wavelength. Depending upon the detailed features that can be identified in well resolved spread F traces one or more of the above mechanisms can be invoked for interpreting them.…”

Section: Introductionmentioning

confidence: 99%

Equatorial spread F echo and irregularity growth processes from conjugate point digital ionograms

Abdu

Batista

Reinisch

et al. 2011

2011 XXXth URSI General Assembly and Scientific Symposium

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Spread F irregularity signatures in the form of range spreading F layer traces are examined in Digisonde ionograms from dip equatorial and conjugate sites in Brazil, to determine the dominant process/mechanism of echo returns from the irregularity structures. A significant component of the ESF echo structures is found to be consistent with them originating from coherent back-scattering at field line perpendicular directions. The spread range of the echoes is found to increase linearly with the top frequency of the echo trace. Further, the irregularity strength is asymmetric at conjugate sites.

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A theoretical model for equatorial ionospheric spread-F echoes in the HF and VHF bands

Cited by 31 publications

References 146 publications

Presunrise spread F at Fortaleza

Presunrise spread F at Fortaleza

Effects of Strong Scattering on Transionospheric Propagation

Equatorial spread F echo and irregularity growth processes from conjugate point digital ionograms

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