VLF Waveguide Propagation: The Basics

Lynn, K. J. W.

doi:10.1063/1.3512893

Cited by 17 publications

(7 citation statements)

References 46 publications

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“…Though the ITU recommendation says that this wave-hop method is preferably used at frequencies above 60 kHz, several papers on the comparison of field intensity by both methods of waveguide and wave-hop, have yielded that a good agreement is obtained between the two, even at frequencies down to 20 kHz (see a recent review by Lynn [39]). This is the reason why we adopt a simpler wave-hop method in this paper.…”

Section: Some Explanation Of Wave-hop Theorymentioning

confidence: 99%

On the Tempo-Spatial Evolution of the Lower Ionospheric Perturbation for the 2016 Kumamoto Earthquakes from Comparisons of VLF Propagation Data Observed at Multiple Stations with Wave-Hop Theoretical Computations

Asano¹,

Hayakawa²

2018

OJER

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There have been published many papers on VLF (very low frequency) characteristics to study seismo-ionospheric perturbations. Usually VLF records (amplitude and/or phase) are used to investigate mainly the temporal evolution of VLF propagation anomalies with special attention to one particular propagation path. The most important advantage of this paper is the simultaneous use of several propagation paths. A succession of earthquakes (EQs) happened in the Kumamoto area in Kyusyu Island; two strong foreshocks with magnitude of 6.5 and 6.4 on 14 April (UT) and the main shock with magnitude 7.3 on 15 April (UT). Because the EQ epicenters are not far from the VLF transmitter (with the call sign of JJI in Miyazaki prefecture), we can utilize simultaneously 8 observing stations of our network all over Japan. Together with the use of theoretical computations based on wave-hop theory, we try to trace both the temporal and spatial evolutions of the ionospheric perturbation associated with this succession of EQs. It is found that the ionospheric perturbation begins to appear about two weeks before the EQs, and this perturbation becomes most developed 5-3 days before the main shock. When the perturbation is most disturbed, the maximum change in vertical direction is depletion in the VLF effective ionospheric height of the order of 10 km, and its horizontal scale (or its radius) is about 1000 km. These spatio-temporal changes of the seismo-ionospheric perturbation will be investigated in details in the discus-How to cite this paper: Asano, T. and Hayakawa, M.

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Section: Some Explanation Of Wave-hop Theorymentioning

confidence: 99%

On the Tempo-Spatial Evolution of the Lower Ionospheric Perturbation for the 2016 Kumamoto Earthquakes from Comparisons of VLF Propagation Data Observed at Multiple Stations with Wave-Hop Theoretical Computations

Asano¹,

Hayakawa²

2018

OJER

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“…During daytime, EIWG allows first-order mode to reach the receiver, whereas the nighttime supports propagation of higher-order modes too to reach the receiver. The number of modes reaching the receiver also depends on the width of EIWG, which ultimately depends on the state of D region of the ionosphere [Lynn, 2010]. Any perturbation in the D region results in changes in the number of modes reaching the receiver which in turn alters the condition for modal interference to cause a shift in the terminator time.…”

Section: Discussionmentioning

confidence: 99%

The 25 April 2015 Nepal Earthquake: Investigation of precursor in VLF subionospheric signal

Maurya

Venkatesham²,

Tiwari³

et al. 2016

JGR Space Physics

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We present a critical analysis of the observations and interpretation of VLF subionospheric measurements related to the main Nepal Gorkha earthquake which occurred on 25 April 2015 (Mw7.8) and its major aftershock on 12 May 2015 (Mw7.3). The VLF narrowband signal used is from North West Cape (NWC) (19.8 kHz) VLF transmitter located in Australia and recorded at Allahabad (latitude 25.41°N, longitude 81.93°E). Allahabad is located very close (~360 km) to these earthquake epicenters. Two widely used analysis, viz., (1) terminator time and (2) nighttime fluctuation techniques, are applied to extract seismic related effects in the NWC narrowband VLF data. The terminator time analysis yields statistically significant shifts of ~45 and ~26 min, respectively, in evening terminator time in the NWC VLF amplitude signal, 1 day before both the earthquakes. The nighttime fluctuation method shows a consistent, statistically significant, increase in three parameters 1 day before the earthquake. The observed terminator time and nighttime fluctuation shifts were associated with these earthquakes only after scrutinizing possible contributions from other potential sources such as solar activity; other earthquakes on the signal path; and meteorological disturbances such as lightning activity, wind speed, and temperature along the transmitter‐receiver great circle path. The VLF subionospheric signal analysis results unambiguously point toward the presence of seismically excited atmospheric gravity waves during these major earthquakes and their important role in providing the coupling between the seismic source region and overlying ionosphere.

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“…The electromagnetic field at any point in this waveguide is decomposed into a series of independent field structures, called modes , propagating with different velocities. The vertical electric field strength between the ground and the ionosphere can be written as a sum of those waveguide modes (Lyn, ). The ionosphere is generally assumed to be inhomogeneous and anisotropic, and the ground is of finite conductivity, while the ionospheric and ground parameters should be changing with propagation path.…”

Section: Probable Influence Of Extraterrestrial X‐rays On Vlf Propagamentioning

confidence: 99%

Lower Ionospheric Plasma‐Chemical Evolution and VLF Signal Modulation by a Series of SGR X‐Ray Bursts: Numerical Simulation With an Ion‐Chemistry Model

2018

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The X‐ray and gamma ray radiation from astrophysical transient sources, like X‐ray bursts from soft gamma repeaters (SGRs) and gamma ray bursts (GRBs), can affect the plasma properties of the lower ionosphere and middle atmosphere. Multiple very low frequency (VLF) receivers in South America, with an unprecedented high time resolution of 20 ms, detected one such series of bursts from SGR J1550‐5418 on 22 January 2009. Due to lack of other suitable means of observation corresponding to the lower part of Earth's ionosphere (∼60–100 km), the VLF detection and analysis of transient ionizing events (mostly of solar origin) has emerged as an excellent method to investigate various chemical and plasma characteristics at these heights. Extragalactic events, like SGR bursts and GRBs, with sharp modulation in their radiation time profile and very high energy photon abundances provide most unique opportunities of such studies with the possibility of extending even lower heights in the atmosphere. Here, for the first time, an extensive computer model, consisting of the combination of Monte Carlo ionization rate computation, a one dimensional atmospheric chemistry module, and VLF waveguide mode calculation, for the reconstruction of VLF signal modulation produced by SGR X‐ray burst starting from the observed spectrum and lightcurve of the event is presented. We gain some valuable insight on the nature of chemical and dynamic evolution over the entire height range of the atmosphere examined from the exercise.

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VLF Waveguide Propagation: The Basics

Cited by 17 publications

References 46 publications

On the Tempo-Spatial Evolution of the Lower Ionospheric Perturbation for the 2016 Kumamoto Earthquakes from Comparisons of VLF Propagation Data Observed at Multiple Stations with Wave-Hop Theoretical Computations

On the Tempo-Spatial Evolution of the Lower Ionospheric Perturbation for the 2016 Kumamoto Earthquakes from Comparisons of VLF Propagation Data Observed at Multiple Stations with Wave-Hop Theoretical Computations

The 25 April 2015 Nepal Earthquake: Investigation of precursor in VLF subionospheric signal

Lower Ionospheric Plasma‐Chemical Evolution and VLF Signal Modulation by a Series of SGR X‐Ray Bursts: Numerical Simulation With an Ion‐Chemistry Model

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