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.

Very low frequency earthquakes related to small asperities on the plate boundary interface at the locked to aseismic transition

Abstract: [1] Very low frequency (VLF) seismic signals observed in southwestern Japan are evidently radiated from shear slips on the upper surface of the subducting Philippine Sea Plate We used grid moment tensor inversion and centroid moment tensor inversion to calculate 242 moment tensor solutions with moment magnitudes between 31 and 38 from continuous seismograms recorded over a 5 year period by using a very dense broadband seismic network At least 5–10 sequences of repetitive activity were observed during the 5 years The VLF events formed clustered distributions along the 35 km isodepth contour of the subducting plate surface The nodal planes (which dip landward) of moment tensor solutions of the VLF events reflected the configuration of the subducting plate interface The slip vectors were consistent with the direction of movement of the subducting plate; the dip and strike of the slip vectors clearly reflected the configuration of the upper surface of the subducting plate We found that the rates of seismic moment release per unit area associated with five major VLF clusters were very similar, although both the seismic magnitudes and sizes of the clusters varied considerably The rate of seismic moment released from detectable VLF sources was 01% of the rates of short-term slow slip events, suggesting that the source areas occupied only 01% of the fault segment on which the short-term slow slip events occurred

On the correlated spectral and timing properties of 4U 1636-53: An atoll source at high accretion rates

Abstract: We analyze ∼600 ks data from the X-ray observatory Rossi X-ray Timing Explorer of the neutron star low mass X-ray binary and atoll source 4U 1636-53. These observations span almost three years, from April 1996 to February 1999. The color-color and hardness-intensity diagrams show significant secular shifts of the atoll track, similar to what is observed for some Z sources. These are most evident in the hardness-intensity diagram, where shifts in intensity up to ∼20% are observed. We find that the intensity shifts in the hardness-intensity diagram are responsible for the parallel tracks observed in the kilohertz quasi periodic oscillations frequency vs. intensity diagram. While the parallel tracks in the frequency vs. color plane partially overlap, systematic long term shifts are still evident. We also study the broad band power spectra of 4U 1636-53 as a function of the source position S a along the track in the color-color diagram. These power spectra are all characteristic of the lower and upper banana state in atoll sources, showing very low frequency noise, band limited noise, and sometimes one or two kHz QPOs. We find that the very low frequency noise in some intervals is not well described by a power law because of an excess of power between 20 and 30 mHz, which can be fitted by a Lorentzian. Also, the characteristic frequency of the band limited noise shows a trend to decrease with increasing S a at high S a values.

Diurnal distribution of ELF, VLF, and LF noise at high latitudes as observed by Alouette 2

Abstract: Statistical studies have been made of the diurnal and latitudinal occurrence and intensity patterns of ELF, VLF, and LF whistler-mode noise emissions observed with the Alouette 2 satellite. The ELF emissions occur characteristically below 1 kHz, are peculiar to the daylight hours, and show a peak in average intensity in the invariant latitude range of 50°–70°. In the VLF range, broadband emissions extending upward from the LHR frequency show a maximum average intensity near local noon and a Λ of about 77°. Along the auroral oval toward earlier and later hours, they show a decreasing intensity. The apparent high-frequency end of this emission band extends upward from 100 kHz to the local fN or fH frequency in the LF range. The LF emissions were studied at a fixed frequency of 200 kHz, and maximum intensities were found along the day and evening portions of the auroral oval. This type of noise also shows a latitude dependence on Kp similar to that of the auroral phenomena. A second region of peak intensity, at about the position of the nighttime plasmapause, appears in the LF statistical results, but a complete study has not been made of that region.

VLF heating of the lower ionosphere

Abstract: A controlled wave-injection experiment with a 28.5 kHz transmitter having a radiated power of 100 kW has revealed evidence of ionospheric heating by the VLF waves. Calculations indicate that the observed effect can be attributed to the absorption of wave energy in the lower ionosphere, which is estimated to result in a 30% enhancement in the collision frequency at 85 km. This process also represents a new means of direct coupling of lightning energy to the lower ionosphere.

The low‐frequency cutoff of ELf emissions

Abstract: Ionospheric LF radio noise cut-off near proton gyrofrequency, discussing satellite ELF and VLF observations