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Observations of amplitude saturation in ELF/VLF wave generation by modulated HF heating of the auroral electrojet
Author(s) -
Moore R. C.,
Inan U. S.,
Bell T. F.
Publication year - 2006
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2006gl025934
Subject(s) - electrojet , amplitude , physics , saturation (graph theory) , amplitude modulation , computational physics , geophysics , frequency modulation , radio frequency , optics , magnetic field , telecommunications , earth's magnetic field , mathematics , quantum mechanics , combinatorics , computer science
We present detailed observations of the onset of amplitude saturation in ELF/VLF waves generated via modulated HF heating of naturally‐forming, large‐scale current systems, such as the auroral electrojet. Broadband ELF/VLF measurements at a ground‐based receiver located near the High‐Frequency Active Auroral Research Program (HAARP) HF transmitter in Gakona, Alaska, exhibit variations in signal amplitude which are qualitatively consistent with a hard‐limiting approximation of the saturation process. A method to approximate the saturation curve as a function of HF power from experimental data is presented, and the results indicate that a ∼5–10% reduction in generated ELF signal amplitude is typical at the maximum radiated HF power level (771 kW) for modulation frequencies between 1225 Hz and 3365 Hz. For HF transmissions using sinusoidal amplitude modulation, the saturation dominantly affects the second harmonic of the generated ELF/VLF signal, with amplitudes on average 16% lower than expected at the maximum HF power level.