VLF line radiation in the Earth's magnetosphere and its association with power system radiation

Abstract

In a recent experiment, discrete VLF emissions from the magnetosphere were triggered by a transmitter at Siple Station in Antarctica. Spectrograms of these signals as received at the conjugate point, Roberval, Quebec, showed changes in slope, entrainments, and cutoffs at frequencies (several kilohertz) close to the harmonic induction lines from the local 60‐Hz power system. This observation led to the suggestion that harmonic radiation from the power system enters the magnetosphere and interacts with the triggered emissions. New evidence supporting this suggestion has been found in spectrograms of simultaneous recordings made at Roberval and at Siple Station in Antarctica. It is shown that line radiation, near harmonics of 60 Hz, travels along the earth's magnetic field in the whistler mode and is received in the conjugate hemisphere at Siple Station. Echoing of the line radiation between Siple and Roberval is often observed. The magnetospheric lines are usually shifted in frequency by 20–30 Hz with respect to the adjacent induction line, but their spacings are near 120 Hz. They may trigger and cut off emissions as do signals from VLF transmitters. Occasionally, magnetospheric lines are seen with spacings of only 20–30 Hz. This smaller frequency separation and the frequency shift of other lines spaced 120 Hz apart are related to the positive frequency offset of emissions triggered by VLF signals from the Omega navigation transmitters. Harmonic lines of reasonable amplitude (∼10−3 γ) are shown to enhance significantly the precipitation of 2‐keV electrons over the eastern parts of the American continents near L ∼ 4. Some mid‐latitude hiss bands appear to consist of sets of magnetospheric lines and their associated triggered emissions.

VLF transmission induced slot electron precipitation

“…Recent disclosur e of prec~pitatlon of energetic electrons in the inner electron zone (L m 1.5 to 2) by a VLF transmitter located in the region of Gorkiy , USSR (Vampola and • Kuck, 1977;Edgar et 81., 1977), coupled with observations that suggest power-line emissions might be effective in scattering electrons In the outer zone (Helliwell et aL, 1975) and in the slot region of the magnetosphere (Bullough et al, 1976), naturally lead to speculation about the role of VLF transmissions in causing the slot-region and outer zone electron precipitation. A major objection to the hypothesis that VLF transmissions might…”

Magnetospheric line radiation observations at Halley, Antarctica

“…The first report of magnetospheric line radiation (MLR) came from observations made by ground-based receivers at Siple, Antarctica, and Roberval, Quebec [Helliwell et al, 1975]. On spectrograms these lines formed thick parallel tracks with frequencies in the range 2-5 kHz, widths of about 30 Hz, and separations commonly about 120 Hz.…”

“…It was postulated that PLHR could propagate in the magnetosphere in the whistler mode, where it might be amplified by wave-particle interactions and alter near-Earth geospace. PLHR could act as the "seed" interacting nonlinearly with trapped particles to produce magnetospheric line radiation (MLR) in frequency by many hundreds of hertz over a few seconds and then on encountering a particular induction line harmonic were entrained, cut off, or had the slope of their frequency variation reversed [Helliwell et al, 1975].…”

Electric field of the power terrestrial sources observed by microsatellite Chibis‐M in the Earth's ionosphere in frequency range 1–60 Hz

“…The first ionospheric/magnetospheric effects caused by power line currents in a few kilohertz range were discovered both during ground [e.g., Helliwell et al, 1975;Park, 1977] and satellite observations [e.g., Bullough et al, 1976;Luette et al, 1977]. Direct signals from power lines were recorded in the ionosphere by LEO satellites mainly as a set of few harmonics a multiple of 50 or 60 Hz in frequency range about 1-8 kHz.…”