Physics
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsm21a0304b&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #SM21A-0304
Physics
0654 Plasmas, 0689 Wave Propagation (2487, 3285, 4275, 4455, 6934), 2716 Energetic Particles: Precipitating, 2774 Radiation Belts, 7807 Charged Particle Motion And Acceleration
Scientific paper
On the basis of analytical models, it is commonly believed that VLF signals from powerful ground based transmitters determine the lifetimes of energetic radiation belt electrons (100 keV - 1.5 MeV) on L shells in the range 1.3 - 2.8 [e.g., Abel and Thorne, 1998]. The primary mechanism of interaction is believed to be gyro- resonance. To test this hypothesis, one needs to know the characteristics of the VLF signals in the radiation belts, as well as the characteristics of the energetic electron precipitation produced by these VLF signals. To these ends, Stanford University has recently carried out a series of experiments in which the 21.4 kHz signals from the US Navy transmitter in Hawaii (NPM) are keyed in a regular OFF/ON pattern designed to reveal any energetic electron precipitation that may be attributed to the transmitter signals. The subject of the present paper concerns the characteristics of the 21.4 kHz signals in the radiation belts. VLF plasma wave observations from the DEMETER spacecraft suggest that the plasma on the L shells illuminated by the NPM transmitter often contain small-scale magnetic-field-aligned plasma density irregularities. VLF waves propagating within these irregularities will generally excite lower-hybrid waves through linear mode coupling. At any given point along an L shell, the excited lower-hybrid waves will resonate with electrons of higher energy than those which resonate with the input wave. Thus the energetic electron precipitation signature due to an input VLF pulse will be different when magnetic-field-aligned plasma density irregularities are present. We compare the precipitation signatures obtained both with, and without, the irregularities and discuss how our results compare with steady state models such as that of [Abel and Thorne, 1998].
Bell Timothy F.
Inan Umran S.
Kulkarni Pradeep
Parrot Michel
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