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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
TL;DR: The first direct evidence of magnetospheric ducts was obtained from the Stanford University broadband VLF experiments on Ogo 1 and Ogo 3 as mentioned in this paper, where five discrete ground whistler ducts were encountered by Ogo3 on the inbound pass of June 15, 1966, between L = 4.7 and 4.1.
Abstract: While the great majority of ground whistlers are interpreted as indirect evidence of magnetospheric ducts, the first direct evidence of ducts was obtained from the Stanford University broadband VLF experiments on Ogo 1 and Ogo 3. Five discrete whistler ducts were encountered by Ogo 3 on the inbound pass of June 15, 1966, between L = 4.7 and 4.1. Each duct was characterized by reception at the satellite of ducted whistlers with a distinct spectral shape, and of the high-frequency portions of whistlers (leakages) that propagated inward from outer ducts. The data were interpreted in detail by ray tracing in a model magnetosphere that includes ducts of enhanced ionization. The following conclusions resulted: (1) the L shell thicknesses of the observed ducts ranged between 0.035 and 0.070 earth radii, and the interduct separations ranged between 0.017 and 0.18 earth radii; (2) the dimension of the ducts in longitude was estimated to be of the order of 4°, or 0.3 earth radii at the equator, which is a factor of ∼4–8 greater than the L shell dimension; (3) the whistler ducts are much more likely to be enhancements than troughs; (4) the minimum enhancement factors needed to trap frequencies up to half the equatorial electron gyrofrequency are on the order of 8%, with smaller values producing upper cutoffs at lower frequencies; (5) the limited spreading of the calculated leaked rays is in general agreement with the corresponding regions of observation and relative signal amplitudes; (6) the low cutoffs of leaked signals are probably due to accessibility; (7) cyclotron and Landau interactions are likely to play a role in upper cutoffs of leaked signals; (8) the upper cutoff of ground whistlers near fH0/2 is a trapping (rather than absorption) effect; (9) the hydrostatic type of distribution of ionization along the field lines is applicable in the plasmasphere; and (10) the travel times (and frequency of minimum delay) of ducted whistlers can be calculated with good accuracy by assuming purely longitudinal propagation.

210 citations

Journal ArticleDOI
TL;DR: Proton whistler /VLF phenomenon observed in satellite data/ discussing propagation in multicomponent plasma and ion cyclotron mode as mentioned in this paper is discussed in this paper. But it is not discussed in detail.
Abstract: Proton whistler /VLF phenomenon observed in satellite data/ discussing propagation in multicomponent plasma and ion cyclotron mode

206 citations

Journal ArticleDOI
TL;DR: In this paper, the authors developed a model of sferic propagation which is based on an existing frequency domain subionospheric VLF propagation code and derived the electron density profile that most closely matched an observed sferric spectrum.
Abstract: Lightning discharges radiate the bulk of their electromagnetic energy in the very low frequency (VLF, 3–30 kHz) and extremely low frequency (ELF, 3–3000 Hz) bands. This energy, contained in impulse-like signals called radio atmospherics or sferics, is guided for long distances by multiple reflections from the ground and lower ionosphere. This suggests that observed sferic waveforms radiated from lightning and received at long distances (>1000 km) from the source stroke contain information about the state of the ionosphere along the propagation path. The focus of this work is on the extraction of nighttime D region electron densities (in the altitude range of ∼70–95 km) from observed VLF sferics. In order to accurately interpret observed sferic characteristics, we develop a model of sferic propagation which is based on an existing frequency domain subionospheric VLF propagation code. The model shows that the spectral characteristics of VLF sferics depend primarily on the propagation path averaged ionospheric D region electron density profile, covering the range of electron densities from ∼100 to 103 cm−3. To infer the D region density from observed VLF sferics, we find the electron density profile that produces a modeled sferic spectrum that most closely matches an observed sferic spectrum. In most nighttime cases the quality of the agreement and the uncertainties involved allow the height of an exponentially varying electron density profile to be inferred with a precision of ∼0.2 km.

203 citations

Journal ArticleDOI
TL;DR: In this paper, a new technique of long-range (≤6000 km) global lightning geolocation via sferic detection is presented, which catalogs the dominant variation in expected received waveforms in a set of waveform banks, which are then used to estimate the propagation distance and accurately determine the arrival time.
Abstract: [1] Lightning discharges generate broadband electromagnetic pulses with a peak component in the very low frequency (VLF; 3–30 kHz) range. VLF waves propagate through the Earth-ionosphere waveguide with relatively low attenuation, enabling the detection of these radio atmospherics at great distances from the lightning discharge. A new technique of long-range (≤6000 km) global lightning geolocation via sferic detection is presented. This new technique catalogs the dominant variation in expected received waveforms in a set of waveform banks, which are then used to estimate the propagation distance and accurately determine the arrival time. Using three sensors in a trial network, this new technique is used to demonstrate a median accuracy of 1–4 km, depending on the time of day. An overall cloud-to-ground (CG) stroke detection efficiency between ∼40 and 60% is estimated by correlating individual lightning stroke events to data from the National Lightning Detection Network (NLDN). Additional events reported by the trial network are shown to have a tight spatial clustering to storm clusters identified by NLDN, suggesting that many of the unmatched events correspond to weak cloud-to-ground strokes, M components, or cloud pulses. Exploiting an empirical correlation between peak VLF field strength and peak current values reported by NLDN, we also provide unvalidated estimates of the peak current and lightning channel polarity. The trial network does not distinguish between cloud and ground discharges, so these peak current estimates only relate to an Earth-referenced channel current for the subset of reported events that are return strokes.

180 citations

Journal ArticleDOI
01 Dec 1984-Nature
TL;DR: In this paper, the first satellite measurements of electron precipitation by lightning were reported, and the measured energy deposition of these conspicuous lightning-induced electron precipitation (LEP) bursts (∼ 10−3 erg cm−2) is sufficient to deplete the Earth's radiation belts and to alter subionospheric radiowave propagation (≲1 MHz).
Abstract: The broadband very low frequency (VLF, 0.3–30 kHz) radiation from lightning propagates in the Earth–ionosphere cavity as impulsive signals (spherics) and in the dispersive plasma regions of the ionosphere and magnetosphere it propagates as tones of descending or rising frequency (whistlers)1. VLF radio waves propagating in the magnetospheric plasma scatter energetic electrons by whistler-mode wave–particle interactions (cyclotron resonance) into the atmosphere2–6. These electrons, through collisions with the atmospheric constituents, cause localized ionization, conductivity enhancement, visual and ultraviolet light emissions, and brems-strahlung X rays. We have reported previously on the precipitation of energetic electrons from the radiation belts by the controlled injection from the ground of VLF radio waves7,8. Here we report the first satellite measurements of electron precipitation by lightning. The measured energy deposition of these conspicuous lightning-induced electron precipitation (LEP) bursts (∼ 10−3 erg cm−2) is sufficient to deplete the Earth's radiation belts and to alter subionospheric radiowave propagation (≲1 MHz). A one-to-one correlation is found between ground-based measurements of VLF spherics and whistlers at Palmer, Antarctica, and low-altitude satellite (S81-1) measurements of precipitating energetic electrons.

169 citations


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