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Abstract The very‐low frequency (VLF) and low frequency (LF) waves from ground transmitters propagate in the ionospheric waveguide, and a portion of their power leaks to the Earth's inner radiation belt and slot region where it can cause electron precipitation loss. Using Van Allen Probes observations, we perform a survey of the VLF and LF transmitter waves at frequencies from 14 to 200 kHz. The statistical electric and magnetic wave amplitudes and frequency spectra are obtained at 1 < L < 3. Based on a recent study on the propagation of VLF transmitter waves, we divide the total wave power into ducted and unducted portions, and model the wave normal angle of unducted waves with dependences onLshell, magnetic latitude, and wave frequency. At lower frequencies, the unducted waves are launched along the vertical direction and the wave normal angle increases during the propagation until reaching the Gendrin angle; at higher frequencies, the normal angle of unducted waves follows the variation of Gendrin angle. We calculate the bounce‐averaged pitch angle and momentum diffusion coefficients of electrons due to ducted and unducted VLF and LF waves. Unducted and ducted waves cause efficient pitch angle scattering atL = 1.5 and 2.5, respectively. Although the wave power from ground transmitters at frequencies higher than 30 kHz is low, these waves can cause the pitch angle scattering of lower energy (2–200 keV atL = 1.5) electrons, which cannot resonate with the VLF transmitter waves at frequencies below 30 kHz, lightning generated whistlers, or plasmaspheric hiss.
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Flickering Low Frequency Auroral Hiss
Abstract A low‐ and medium‐frequency (LF/MF) receiving system at South Pole Station, using a wide‐beam dipole antenna, measured continuous fully sampled waveforms of more than 100 LF auroral hiss events between June and October 2019. Spectra of fluctuations of LF auroral hiss intensity at selected frequencies between 110 and 530 kHz showed these are broadband, with spectral power monotonically decreasing to an upper bound typically 20–60 Hz, comparable to frequencies reported for optical flickering aurora. Occasionally intervals of periodic fluctuations in auroral hiss intensity occurred, in most cases lasting only tens of cycles. On September 1, 2019, periodic fluctuations lasted thousands of cycles during two 30‐s intervals, at frequencies 125–145 Hz. Close examination showed these to be dispersed with low frequencies arriving before high frequencies by approximately 4.5 ms per 100 kHz. Ray‐tracing calculations and consideration of the Temerin et al. (1986, 1993) mechanisms of flickering aurora shows that the September 1 flickering auroral hiss observations are consistent with resonant amplification of whistler mode noise by an electron beam accelerated and modulated by electromagnetic proton cyclotron waves originating near 4,500 km, with the wave excitation taking place at 2,000–3,000 km.
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- Award ID(s):
- 1911335
- PAR ID:
- 10361990
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Space Physics
- Volume:
- 126
- Issue:
- 4
- ISSN:
- 2169-9380
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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