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Very low frequency

About: Very low frequency is a research topic. Over the lifetime, 1540 publications have been published within this topic receiving 24233 citations. The topic is also known as: VLF.


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Journal ArticleDOI
01 Jan 2020
TL;DR: In this article, the effect of back to back two geomagnetic storms before a strong earthquake happened in Imphal, India on January 4, 2016 (M = 6.7).
Abstract: Study of seismo-ionospheric coupling mechanism demands the quiet geomagnetic condition to eliminate any kind of contamination in the lower atmospheric and ionospheric parameters. In this manuscript, we present the effect of back to back two geomagnetic storms before a strong earthquake happened in Imphal, India on January 4, 2016 (M = 6.7). We studied the lower ionospheric irregularities for the duration of 31 days by computing the nighttime fluctuations in Very Low Frequency (VLF) radio signal received transmitter JJI (22.2 kHz) in Japan at Ionospheric and Earthquake Research Centre & Optical Observatory (IERCOO), Sitapur, India. We also studied the presence of Atmospheric Gravity Wave (AGW) in nighttime VLF signal in lower ionospheric heights and the same computed that from SABER/TIMED satellite. Two geomagnetic storms occurred on December 21, and 31, 2015. By the conventional analysis, we found that there is a significant decrease in nighttime trend and an increase in nighttime fluctuations around 15 days before the earthquake and just on the first storm and thus the pre-seismic effects on VLF signal gets contaminated due to the presence of storms. The wave-like structure in VLF fluctuations shows significant increase in intensity by using Fourier and Wavelet analysis before the earthquake. By analysis of SABER data, we found significant enhancement in AGW around 10 days before the earthquake. As the wavelike structures are coming from neutral acoustics reasons from pressure or temperature variations, this paper exhibits a significant example of contamination in ionospheric parameters due to geomagnetic storm where the acoustics parameters remain un-contaminated.

9 citations

Journal ArticleDOI
TL;DR: In this article, high-resolution pitch angle measurements made by a magnetic focusing electron spectrometer on the S3-3 satellite while in the drift loss cone region of the magnetosphere were used to locate the longitude of precipitation.
Abstract: : Using high resolution pitch angle measurements made by a magnetic focusing electron spectrometer on the S3-3 satellite while in the drift loss cone region of the magnetosphere, characteristics of fluxes of 108 keV to 654 keV electrons precipitated in the inner zone, in the slot region, and in the outer zone of the magnetosphere are all shown to be consistent with the precipitation having been produced by the same ground-based VLF transmitter, UMS. Pitch angle measurements are used to locate the longitude of precipitation. The temporal pattern of transmitter operation obtained from synoptic data from a ground-based VLF receiver is used along with drift-rate calculations to predict the electron energies as a function of L-shell which should be observable by the S3-3 instrument. The predicted energy response is then compared with the in-situ observations, getting complete agreement. Finally, wave-particle resonance calculations are made for each of the three regions. The study indicates that ground-based VLF transmitters, which have previously been shown to produce precipitation in the inner zone and slot regions, are almost certainly instrumental in precipitating electrons in the outer zone also.

9 citations

Book
01 Jan 1975
TL;DR: In this article, an innovative technique is presented for tracking frequency excursions in real time to produce a filterred, quasimonochromatic version of the signal, which is then crossmultiplied in a manner analogous to a Poynting vector calculation to obtain a continuous indication of the wave direction of arrival.
Abstract: : Whistlers and related very low frequency radio signals are guided in ducts of enhanced or reduced ionization along the geomagnetic lines of force of the earth's magnetosphere The signals convey information about the distribution of particles in the plasma through which they have propagated and about the occurrence of wave-particle interactions in the magnetosphere Direction-finding on such signals will aid in locating the ducts and measuring their temporal drifts, thus making an important contribution to studies of magnetospheric convection The signals, although narrowband in nature, exhibit wide frequency excursions in the 1 to 10 kilohertz range An innovative technique is presented for tracking these frequency excursions in real time to produce a filterred, quasimonochromatic version of the signal The voltages induced by the incident wave on two orthogonal loop antennas and a vertical monopole antenna are processed by this method The filtered signals are then cross-multiplied in a manner analogous to a Poynting vector calculation to obtain a continuous indication of the wave direction of arrival The design, construction, and laboratory testing of a prototype instrument are described Field testing of the instrument was performed at Stanford, California, and Roberval, Quebec, Canada Operating at fixed frequencies, the direction-finder produced accurate results on VLF transmissions in the 10 to 20 kilohertz range from NAA, NPG, GBR, and the Omega stations

9 citations

Journal ArticleDOI
TL;DR: In this paper, the authors carried out the prediction of daily nighttime mean very low frequency (VLF) amplitude by using Nonlinear Autoregressive with Exogenous Input Neural Network (NARX NN), which was built based on the daily input variables of various physical parameters such as stratospheric temperature, total column ozone, cosmic rays, Dst, and Kp indices.
Abstract: The electric field amplitude of very low frequency (VLF) transmitter from Hawaii (NPM) has been continuously recorded at Chofu (CHF), Tokyo, Japan. The VLF amplitude variability indicates lower ionospheric perturbation in the D region (60–90 km altitude range) around the NPM-CHF propagation path. We carried out the prediction of daily nighttime mean VLF amplitude by using Nonlinear Autoregressive with Exogenous Input Neural Network (NARX NN). The NARX NN model, which was built based on the daily input variables of various physical parameters such as stratospheric temperature, total column ozone, cosmic rays, Dst, and Kp indices possess good accuracy during the model building. The fitted model was constructed within the training period from 1 January 2011 to 4 February 2013 by using three algorithms, namely, Bayesian Neural Network (BRANN), Levenberg Marquardt Neural Network (LMANN), and Scaled Conjugate Gradient (SCG). The LMANN has the largest Pearson correlation coefficient (r) of 0.94 and smallest root-mean-square error (RMSE) of 1.19 dB. The constructed models by using LMANN were applied to predict the VLF amplitude from 5 February 2013 to 31 December 2013. As a result the one step (1 day) ahead predicted nighttime VLF amplitude has the r of 0.93 and RMSE of 2.25 dB. We conclude that the model built according to the proposed methodology provides good predictions of the electric field amplitude of VLF waves for NPM-CHF (midlatitude) propagation path.

9 citations

Journal ArticleDOI
TL;DR: In this article, three rockets were launched along the magnetic field lines, up to an altitude of ∼400 km, to study the wave-particle interactions that take place during natural VLF emissions.
Abstract: Three rockets were launched along the magnetic field lines, up to an altitude of ∼400 km, to study the wave-particle interactions that take place during natural VLF emissions. The group delay time was measured for the structured elements of dawn chorus, using a correlation technique. This time is shown to be in good agreement in the ascending part of the flight with the theoretical one deduced from the Appleton-Hartree formula with the use of simultaneous ionospheric soundings giving the electron density above the station. Changes at the end of the flight show discontinuities in the electron density profiles and set an upper limit to the area on which VLF signals detected on the ground are coherent. From the intensity measurements, comparison is made with the theory of attenuation and reflection of VLF waves (f<2 kHz) when passing through the ionosphere. A general agreement was found between the theoretical and experimental results, as far as the shape of the amplitude variation as a function of height is considered. Large discrepancies in the absolute values are observed which are attributed to oblique incidence of the waves. Polarization measurements permit us to ascribe a circular polarization to these waves even at VLF, except in the lower ionosphere (h<120 km) where it shows a tendency to become a elliptical.

9 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202320
202232
202156
202048
201942
201852