Modeling of equatorial multifrequency scintillation

Franke, Steven; Liu, C. H.

doi:10.1029/rs020i003p00403

Cited by 18 publications

(23 citation statements)

References 14 publications

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“…For a two-component power law spectrum of density variations in the irregularities, the characteristic scale length is the 'break scale', whereas for a single component power law spectrum, it would be the outer scale. Franke and Liu [1985] thus provided a theoretical explanation for the observation that when VHF scintillations were in the saturated regime, the corresponding C-band scintillations, which were weak, yielded an S 4 -index proportional to s f and hence to (1/t I ), provided the drift velocity of the irregularities, the outer scale, and 'break scale' remained constant.…”

Section: Comparison With Theorymentioning

confidence: 85%

“…By studying the auto-correlation function of 257-MHz scintillations recorded by a single receiver at Ascension Island, Basu et al [1983] had found the inverse of the 50% decorrelation interval to be a good measure of the strength of irregularities whenever the drift speed of the ground scintillation pattern did not vary significantly. Franke and Liu [1985] provided a theoretical explanation for this observation.…”

Section: Space-time Structure Of Uhf Signal Intensitymentioning

confidence: 86%

“…It is well known that in the regime of strong scintillations, the S 4 -index, which is the standard deviation of normalized intensity variations and is used as a measure of the strength of scintillations, is no longer proportional to irregularity strength as measured by the rms variation in electron density [Yeh and Liu, 1982]. In the past, single receiver measurements of VHF, L-and C-band scintillations, at a location near the crest of the EIA, have been used to show that the inverse of the 50% decorrelation time of VHF scintillations may be used to track weak to moderate scintillations on the higher frequencies, since this decorrelation time may be considered to be inversely proportional to the strength of the irregularities, provided the irregularity drift speed and certain characteristics of the power spectrum of the density variations remain unchanged [Basu et al, 1983;Franke and Liu, 1985].…”

Section: Introductionmentioning

confidence: 99%

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L‐band scintillation activity and space‐time structure of low‐latitude UHF scintillations

et al. 2003

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[1] Spatial correlation function of intensity scintillation patterns produced by the propagation of a UHF signal through irregularities in the nighttime low-latitude ionosphere is deduced from an analysis of spaced receiver records of such scintillations. This analysis requires that random temporal variations of the irregularity drift speed be taken into account. It is seen from the results that the occurrence of strong scintillations on an L-band signal requires the presence of short ($20 m) coherence scale lengths in the UHF scintillation pattern obtained in the plane of the receiver. This condition is satisfied near the crest of the equatorial ionization anomaly (EIA) region, but not near the dip equator. In the decay phase of L-band scintillations recorded near the crest of the EIA region, the maximum strength of these scintillations at any point in time is found to be correlated with the magnetic eastward drift speed of the pattern of intensity scintillations on an UHF signal recorded in this region, which is determined mainly by the magnetic eastward drift velocity of the ionospheric irregularites. Dependence of the corresponding strength of UHF scintillations on the drift speed indicates that toward the end of the decay phase of L-band scintillations, the irregularity power spectrum steepens, and the large scale irregularities that remain can cause the UHF signal to be focused in the plane of the receiver, yielding UHF S 4 -indices greater than one, while focusing of the UHF signal is less evident at earlier times when there is focusing of the L-band signal.

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Section: Comparison With Theorymentioning

confidence: 85%

Section: Space-time Structure Of Uhf Signal Intensitymentioning

confidence: 86%

Section: Introductionmentioning

confidence: 99%

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L‐band scintillation activity and space‐time structure of low‐latitude UHF scintillations

et al. 2003

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“…Actual turbulence in the equatorial ionosphere, by contrast, consists of large-scale deterministic structure (equatorial plasma bubbles) with small-scale random structure embedded within these bubbles [17,24]. Furthermore, there is evidence to suggest that a model based on a two-component power law is better able to characterize the plasma turbulence under some circumstances [41]. Despite these limitations, the Wideband Scintillation Model which is based on this formulation has been shown to produce a very satisfactory International Journal of Geophysics description of the scintillation of transionospheric signals at frequencies ranging from VHF to L band (e.g., see [22] and the references therein).…”

Section: Remarks and Conclusionmentioning

confidence: 99%

Latitudinal and Local Time Variation of Ionospheric Turbulence Parameters during the Conjugate Point Equatorial Experiment in Brazil

Carrano

Valladares

Groves

2012

International Journal of Geophysics

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Previous authors have reported on the morphology of GPS scintillations and irregularity zonal drift during the 2002 Conjugate Point Equatorial Experiment (COPEX) in Brazil. In this paper, we characterize the turbulent ionospheric medium that produced these scintillations. Using 10 Hz GPS carrier-to-noise measurements at Boa Vista (2.9 • N, 60.7 • W), Alta Floresta (9.9 • S, 56.1 • W), and Campo Grande (20.5 • S, 54.7 • W), we report on the variation of turbulent intensity, phase spectral index, and irregularity zonal drift as a function of latitude and local time for the evening of 1-2 November 2002. The method of analysis is new and, unlike analytical theories of scintillation based on the Born or Rytov approximations, it is valid when the scintillation index saturates due to multiple-scatter effects. Our principal findings are that (1) the strength of turbulence tended to be largest near the crests of the equatorial anomaly and at early postsunset local times, (2) the turbulent intensity was generally stronger and lasted two hours longer at Campo Grande than at Boa Vista, (3) the phase spectral index was similar at the three stations but increased from 2.5 to 4.5 with local time, and (4) our estimates of zonal irregularity drift are consistent with those provided by the spaced-receiver technique.

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“…For scintillations that are not weak, it is necessary to use strong scatter theory to compute n . In the past, variation of n estimated from S 4 indices for L‐band and C‐band signals recorded at Ascension Island, near the crest of the EIA region, was explained using a phase screen model for the irregularities (Franke & Liu, , ). Theoretical results reported in these papers were obtained by computation of the wavefield on the ground, after the signal propagated through a one‐dimensional phase screen characterized by phase variations produced by the irregularities.…”

Section: Theoretical Results For the Frequency Exponentmentioning

confidence: 99%

Signal Frequency Dependence of Ionospheric Scintillations: An Indicator of Irregularity Spectrum Characteristics

et al. 2019

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Multifrequency scintillation observations show that strong amplitude scintillations on very high frequency (VHF) signals are accompanied by weak L‐band scintillations near the dip equator and strong L‐band scintillations in equatorial ionization anomaly (EIA) region. For several decades this has been attributed to higher ambient plasma density in the EIA region. Recent work suggests that occurrence of stronger L‐band scintillations in the EIA region requires that the intermediate‐scale (~100 m to few km) ionospheric irregularity spectrum in this region be significantly shallower than that in the equatorial region. However, this has not been established so far. Signal frequency dependence of amplitude scintillations is characterized by the frequency exponent that determines the dependence on signal frequency of the S4 index: the standard deviation of normalized intensity fluctuations. In this paper, theoretical calculations of the frequency exponent for VHF and L‐band signals are carried out using different irregularity spectra and compared with observations in order to characterize power‐law irregularity spectra in different latitude zones. Intermediate‐scale irregularities in the equatorial and low‐latitude region, which are aligned with the geomagnetic field, are described by a two‐dimensional model. Model simulations show that the frequency exponent derived from S4 indices for VHF and L‐band signals is determined only by the characteristics of the irregularity spectrum and hence can be utilized to identify the nature of the power‐law irregularity spectrum. Frequency exponents computed using VHF and L‐band observations near the dip equator and EIA regions show distinct patterns, which clearly indicate steep and shallow irregularity spectra, respectively, in these regions.

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Modeling of equatorial multifrequency scintillation

Cited by 18 publications

References 14 publications

L‐band scintillation activity and space‐time structure of low‐latitude UHF scintillations

L‐band scintillation activity and space‐time structure of low‐latitude UHF scintillations

Latitudinal and Local Time Variation of Ionospheric Turbulence Parameters during the Conjugate Point Equatorial Experiment in Brazil

Signal Frequency Dependence of Ionospheric Scintillations: An Indicator of Irregularity Spectrum Characteristics

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