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.

VLF waves from ground‐based transmitters observed by the Van Allen Probes: Statistical model and effects on plasmaspheric electrons

Abstract: Whistler-mode Very Low Frequency (VLF) waves from powerful ground-based transmitters can resonantly scatter energetic plasmaspheric electrons and precipitate them into the atmosphere. A comprehensive 4-year statistics of Van Allen Probes measurements is carried out to assess their consequences on the dynamics of the inner radiation belt and slot region. Statistical models of the measured wave electric field power and of the inferred full wave magnetic amplitude are provided as a function of L, magnetic local time, season, and Kp over L=1-3, revealing the localization of VLF wave intensity and its variation with geomagnetic activity over 2012-2016. Since this VLF wave model can be directly used together with existing hiss and lightning-generated wave models in radiation belt simulation codes, we perform numerical calculations of the corresponding quasilinear pitch angle diffusion rates, allowing us to demonstrate the crucial role played by VLF waves from transmitters in energetic electron loss at L<2.5.

Scattering Pattern of Lightning-Induced Ionospheric Disturbances Associated with Early/Fast VLF Events

Abstract: Simultaneous observations of early/fast Very Low Frequency (VLF) events at nine closely spaced (65 km) sites are used together with a numerical model of the propagation and scattering of VLF signals in the earth- ionosphere waveguide to directly measure the scattering pat- tern of associated ionospheric disturbances. In cases when the causative lightning is within 700 km of the north-south array of observing sites, early/fast VLF events are typically observed at no more than 2 or 3 sites, which indicates a nar- row beam of the scattered signal in the forward direction. In the dierent cases studied, forward scattering patterns exhibit 15 dB beamwidths of less than 30 consistent with horizontal extent of 90 30 km.

A study of ionospheric response to regional seismic activity by VLF radio sounding

Abstract: Electric field strength nighttime fluctuations in subionospheric signals of very low frequency (VLF) on Omega, Tsushima-Chofu (Tokyo) and NWC, Australia-Chofu propagation paths recorded during March–August, 1997 were studied for searching for correlation with seismic activity. Wave-like anomalies in VLF Omega signal with periods of a few hours were observed 1–3 days before or on the day of moderately strong earthquakes of magnitudes 5–6.1. Analysis of the correlation between regional seismic activity around Tokyo and dispersion of VLF fluctuations revealed that maximal correlation was observed during pre-seismic periods for shallow earthquakes (focal depth less than 40 km) that occurred at distances up to 350–400 km from receiving place. Spectral analysis of the earthquake catalogue has shown rhythmical variations of seismic activity integrated over large areas with periods of 4–14 days. Similar periodic components are observed in fluctuations of VLF signals propagating over the NWC-Chofu path. For both VLF propagation paths, a 27-day periodicity was found in fluctuations of signals that can be referred to as tidal or solar rotation influence.

Dual-radio communication apparatus, and an operating method thereof

Abstract: A dual-radio communication apparatus has a first radio device, such as a Bluetooth radio, for use in a first frequency band, and a second radio device, such as a Globalstar satellite radio, for use in a second frequency band, which is proximate to the first frequency band. The communication apparatus also has a controller coupled to the first and second radio devices. The first radio device may comprise a frequency-hopping spread-spectrum transmitter. Moreover, the first radio device has a first operating mode employing a first frequency range. The first radio device also has a second operating mode employing a second frequency range, which is smaller than the first frequency range. The controller is adapted to set the first radio device in its second operating mode, when the second radio device is in operation, and otherwise set the first radio device in its first operating mode.

Near-Relativistic Solar Electrons and Type III Radio Bursts

Abstract: Recently it has been found that the inferred injection times of greater than 25 keV electrons are up to 30 minutes later than the start times of the associated type III radio bursts at the Sun. Thus it has been suggested that the electrons that produce type III bursts do not belong to the same population as those observed above 25 keV. This paper examines the characteristics and circumstances of 79 solar electron beam events measured on the ACE spacecraft. Particular attention is paid to the very low frequency emissions of the associated radio bursts and the ambient conditions at the arrival times of the electrons at the spacecraft. It is found that the inferred greater than 25 keV electron injection delays are correlated with the times required for the associated radio bursts to drift to the lowest frequencies. This suggests that the electrons responsible for the radio emission and those observed above 25 keV are part of a single population, and that the electrons both above and below 25 keV are delayed in the interplanetary medium. Further evidence for a single population is the general correspondence between electron and local radio intensities and temporal profiles. It is found that the delays increase with the ambient solar wind density consistent with the propagation times of the electrons being determined by the characteristics of the interplanetary medium. However it is known that particle arrival times at 1 AU are a linear function of inverse particle speed. Conventionally such a relationship is taken to indicate scatter-free propagation when inferred path lengths lie close to 1.2 AU, as they do for the electron events studied here. These conflicting interpretations require further investigation.