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.

A theory of discrete VLF emissions from the magnetosphere

Abstract: Magnetospheric discrete VLF emissions, discussing gyroresonance extension, resonant electron and emission frequency

Cyclotron instabilities and electromagnetic emission in the ultra low frequency and very low frequency ranges

Abstract: A model for the generation of pearl-type micropulsations in the 0.1–5 cps range is presented. Under a different set of conditions, the model is also applicable to the generation of VLF emissions in the whistler mode. It is proposed that a beam of trapped protons at L ≥ 4, supersonic with respect to the local Alfven speed, emits hydromagnetic waves at a frequency corresponding to the occurrence of a cyclotron instability. These hydromagnetic waves propagate along the earth's field lines and are reflected back along the line at the ionosphere. On each pass of a wave packet through the proton beam, energy is supplied to the wave by the particles via the instability. Certain features of the observed fine structure of micropulsations are explained with the concept of bouncing hydromagnetic wave packets. A possible candidate for the necessary proton beam is the belt of 200–500 kev protons observed by Davis and Williamson, but there are other candidates as well, including low-energy ring currents at L ≃ 6. VLF emission in the 1–10 kc/s range may be produced by a similar instability if a beam of energetic electrons is present.

Radio interferometric geolocation

Abstract: We present a novel radio interference based sensor localization method for wireless sensor networks. The technique relies on a pair of nodes emitting radio waves simultaneously at slightly different frequencies. The carrier frequency of the composite signal is between the two frequencies, but has a very low frequency envelope. Neighboring nodes can measure the energy of the envelope signal as the signal strength. The relative phase offset of this signal measured at two receivers is a function of the distances between the four nodes involved and the carrier frequency. By making multiple measurements in an at least 8-node network, it is possible to reconstruct the relative location of the nodes in 3D. Our prototype implementation on the MICA2 platform yields an average localization error as small as 3 cm and a range of up to 160 meters. In addition to this high precision and long range, the other main advantage of the Radio Interferometric Positioning System (RIPS) is the fact that it does not require any sensors other than the radio used for wireless communication.

Subionospheric VLF signal perturbations possibly related to earthquakes

Abstract: A likely VLF subionospheric signal effect related to seismic activity was first reported by Hayakawa et al. [1996a, b] in association with the great Kobe earthquake. We have analyzed similar data during periods around 10 other great earthquakes (magnitude M>6) in order to understand the main features of such an effect. The following characteristics emerged from our analysis: The effect appears as a transient oscillation with a 5- to 10-day period, which is initiated a few days before a large earthquake and decays over a few days to weeks after it. It is mainly related to crustal earthquakes. It appears when resonant atmospheric oscillations with periods in a range of 5–11 days exist before the earthquake. The seismic influence on the VLF signal is probably explained by the generation of long-period gravity waves during the earthquake process and their intensification at heights of 70–90 km.

Reviving Fossil Radio Plasma in Clusters of Galaxies by Adiabatic Compression in Environmental Shock Waves

Abstract: We give for a plasma with a history of several expansion and contraction phases an analytical model of the evolution of a contained relativistic electron population under synchrotron, inverse Compton and adiabatic energy losses or gains. This is applied to different scenarios for evolution of radio plasma inside the cocoons of radio galaxies, after the activity of the central engine has ceased. It is demonstrated that fossil radio plasma with an age of even up to 2 Gyr can be revived by compression in a shock wave of large-scale structure formation, caused during the merging events of galaxy clusters, or by the accretion onto galaxy clusters. We argue, that this is a highly plausible explanation for the observed cluster radio relics, which are the regions of diffuse radio emission found in clusters of galaxies, without any likely parent radio galaxy seen nearby. An implication of this model is the existence of a population of diffuse, ultra-steep spectrum, very low frequency radio sources located inside and possibly outside of clusters of galaxies, tracing the revival of aged fossil radio plasma by the shock waves associated with large-scale structure formation.