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.

Diffraction of VLF radio waves by polar ice caps

Abstract: A rudimentary theory is outlined for the phenomenon of diffraction of long radio waves by continental land masses for long seawater paths. The results would seem to be particularly relevant to observations by Barr for a path that just grazes the coast of Antarctica.

Some relationships between aurora and natural vlf and lf noise at plateau station, antarctica

Abstract: : Various relationships between aurora as observed in all-sky photographs and natural noise at frequencies of 1.5, 8, 50, and 110 kHz are found from data taken at Plateau Station, Antarctica, during the austral winter of 1966. The investigation is carried out in two parts: diurnal variations in occurrence are found for aurora and noise, and a minute-by-minute examination of relationships is made for a one-week period. Diurnal occurrence of noise at 110 kHz peaks before magnetic midnight at about the same time as a peak occurs in the more familiar diurnal curves of occurrence of noise at 8 kHz and of aurora. Examples are shown of several events in which associations between variations in noise and variations in auroral elevation, intensity, form, and rate of change can be found from detailed comparison of the data. The majority of all noise changes during the week is found to coincide with changes in the aurora.

Very low frequency phase perturbations and the soviet high-altitude nuclear bursts of October 22 and 28, 1962: 1. Observations and inferred radiation belts

Abstract: On October 22 and 28, 1962, nuclear explosions over central Asia produced ionospheric D-layer perturbations as monitored on various VLF paths in the northern hemisphere Delayed VLF effects due to trapped particles averaged 53% of the normal diurnal change for the burst of October 22, and 29% for the burst of October 28 The types of particles and their energies were the same for both detonations, but differences existed in the spatial extent of the radiation belts producing the VLF phase perturbations The trapped particles were electrons with E ≲ 4 Mev and protons in the range 23 to 46 Mev The electron spectrum is composed of fission and neutron-decay β particles, the latter predominating for E < 078 Mev Protons <23 Mev may have also been present, but those with E < 1 Mev cannot penetrate into the D region and are of no direct VLF interest With the dipole field approximation, for the detonation of October 22, fission and neutron-decay β particles were trapped in a region bounded by field lines intersecting the earth's surface in a range extending at least from 365° to 56° geomagnetic (for the real field the shells are 175 ≤ L ≤ 376) For October 28, fission β particles were confined to areas <49°N (L < 232) and probably to field lines around that passing through the burst point (at 365°N and L = 175); this type of confinement also existed for 23- to 46-Mev protons after both nuclear bursts For October 28, effects due to neutron-decay β particles were found at 49°–51°N (232 ≤ L ≤ 279), a region which formed the outer boundary for these trapped particles For the burst of October 22, a prompt effect was observed on the GBR to APL transmission

Low frequency signal spectrum analysis for strong earthquakes

Abstract: We examined changes in the spectral composition of the low frequency (LF) subionospheric signals from the NRK transmitter (37.5 kHz) in Iceland that were received in Bari (Italy) relative to the earthquake that occurred in L’Aquila on April 6, 2009. In our previous studies, we have reported the occurrence of preseismic night-time anomalies using observations from three receivers located in Bari, Graz (Austria) and Moscow (Russia). The strongest anomalies in the signals were observed in the NRK-Bari propagation path during the period 5-6 days before the L’Aquila earthquake, as well as during the series of aftershocks. During this period, similar very low frequency (VLF)/LF amplitude anomalies were also observed along several other propagation paths that crossed the L’Aquila seismogenic zone. Spectral analysis of the LF signals filtered in the frequency range 0.28 mHz to 15 mHz shows differences in the spectra for seismo-disturbed days when compared to those for either quiet or geomagnetically disturbed days. These spectral anomalies, which are only observed in the propagation path between NRK and Bari, contain signals with periods of about 10 min to 20 min. These periodic signals are absent both in the spectra of the undisturbed signals for the control paths, and in the spectra of the signals received during geomagnetic storms. The same changes in the spectral composition were observed in the analysis of LF (40 kHz) signals from the JJY transmitter in Japan that were received in Petropavlovsk-Kamchatsky (Russia) during the occurrence of three strong earthquakes with M ≥7.0. The results of this study support the theoretical prediction that the possible mechanism for energy penetration from the origin of an earthquake through the atmosphere and into the ionosphere is based on the excitation and upward propagation of internal gravity waves.