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 signatures of ionospheric disturbances associated with sprites

Abstract: VLF perturbations on signals propagating along great-circle-paths (GCP) through electrically active midwest thunderstorms are associated with luminous high altitude glows (referred to as sprites) observed from aircraft or ground. The data constitutes the first evidence that the physical processes leading to sprites also alter the conductivity of the lower ionosphere.

Equion, an Equatorial Ionospheric Irregularity Experiment

Abstract: : This paper describes a coordinated rocket and ground based study to investigate Equatorial Spread-F irregularities. Measurements by the Jicamarca backscatter radar, ionosondes, airglow instrumentation and of radio scintillations were correlated with high spatial resolution measurements of electron densities, particle fluxes and VLF-ELF fields from a rocket probe. Experimentally the authors find: (1) Very high positive and negative electron density gradients are responsible for the enhanced radar echoes; (2) Energetic particles are not part of the Spread-F phenomena; (3) wave measurements are strongly correlated with the Doppler character of the radar signals; and (4) That there is a one to one correspondence of the large scale irregularities responsible for scintillations of satellite radio transmissions, and ionosonde spread echoes with the small scale irregularities responsible for the backscatter of VHF radar signals. Implications of the data are discussed.

Scattering of energetic trapped electrons by very‐low‐frequency waves

Abstract: The role of VLF waves in precipitating fast electrons is studied. It is found that, by Doppler-shifting whistler frequencies (1–10 kc/s) up to the local Larmor frequency, a resonant interaction of the type proposed by Dragt and Wentzel (for interaction of protons with hydromagnetic waves) can cause the mirror points of the electrons to move randomly. The conditions for resonance lead to a very characteristic dependence on L of the regions of the magnetosphere where VLF waves can effectively precipitate electrons. In general, one expects to see, in a plot of flux versus L, two peaks separated by a broad minimum, the first peak near L ≃ 1.2 and the second near L ≃ 2. Such peaks have been seen by several experimenters. In certain regions of space it may be that whistlers can dominate the lifetimes of trapped electrons, especially for L ≳ 2.

Direct observation of radiation belt electrons precipitated by the controlled injection of VLF signals from a ground‐based transmitter

Abstract: Radiation belt electrons precipitated by controlled injection of VLF signals from a ground based transmitter have been directly observed for the first time. These observations were part of the SEEP (Stimulated Emission of Energetic Particles) experiment conducted during May-December 1982. Key elements of SEEP were the controlled modulation of VLF transmitters and a sensitive low altitude satellite payload to detect the precipitation. An outstanding example of time-correlated wave and particle data occurred from 8680 to 8740 seconds. U. T. on 17 August 1982 when the satellite passed near the VLF transmitter at Cutler, Maine (NAA) as it was being modulated with a repeated ON (3--s)/OFF (2--s) pattern. During each of twelve consecutive pulses from the transmitter the electron counting rate increased significantly after start of the ON period and reached a maximum about 2 seconds later. The measured energy spectra revealed that approximately 15 to 50 percent of the enhanced electron flux was concentrated near the resonant energies for first order cyclotron interactions occurring close to the magnetic equator with the nearly monochromatic waves emitted from the transmitter.

The Numerical Calculation of Wave-Fields, Reflexion Coefficients and Polarizations for Long Radio Waves in the Lower Ionosphere. II

Abstract: The characteristics of radio waves of low and very low frequency reflected from numerical models of electron density and collision frequency are calculated by the methods described in the preceding paper (Pitteway 1964). The models used are based on those found by cross-modulation experiments and approximate to those likely to be found in the ionosphere. The effects of changing the models are investigated with the object of developing methods of solving the inverse problem of deducing the ionization structure from the experimental data on long and very long wave propagation. The relations between the computed and observed characteristics are examined in a preliminary way.