Effects of Power Line Radiation into the Magnetosphere
VLF power line radiation (PLR) can cause triggering, suppression and entrainment of whistler-mode chorus emissions in the magnetosphere. High-altitude OGO-3 spectral data show evidence of enhanced chorus activity over centers of population and industry, indicating that PLR may play a significant role in the excitation of VLF whistler-mode noise and the associated precipitation of electrons. Sampled OGO-3 data showed chorus elements starting in multiples of 50 Hz in the European-Siberia sector, of 60 Hz in the United States-Canada sector, of either 50 or 60 Hz in the Alaska (60-Hz system)-New Zealand (50-Hz system) sector. Low-altitude Ariel III data on the intensity of all types of VLF activity at 3.2 kHz showed enhanced noise over populated areas and their conjugates, but the relative contributions of lightning and PLR were not assessed. VLF data from the low-altitude OGO-4 scanning receiver (150–1500 Hz; 200 orbits; 1966–67) detected PLR from both 50-Hz and 60-Hz systems with average intensities near 1.0 mγ; PLR intensities greater than 10 mγ were detected less than 10% of the time. Intensities were low in the midnight and dawn sector.
Antarctic data from Eights (L = 3.9; 1963–65) and Siple Station (L = 4.2; 1973–75) show strong control o f chorus frequencies by PLR. Activity peaks at 3 kHz and at 12 LT. 2–4 kHz noise (mostly chorus) shows a distinct minimum on Sunday, as does average power consumption in the conjugate area.
To explain the observed geophysical variations in VLF wave activity, it is suggested that PLR acts to lower the threshold for wave growth, just as in the Siple Station controlled triggering experiments. Geographical localization of VLF waves is expected to cause corresponding localization of particle precipitation. However, global average precipitation would not necessarily be affected.
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