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Title: Nonlinear wave growth theory of coherent hiss emissions in the plasmasphere
Authors: Omura, Yoshiharu  kyouindb  KAKEN_id
Nakamura, Satoko
Kletzing, Craig A.
Summers, Danny
Hikishima, Mitsuru
Author's alias: 大村, 善治
Keywords: hiss
plasmasphere
whistler mode wave
wave-particle interaction
nonlinear theory
coherent wave
Issue Date: Sep-2015
Publisher: American Geophysical Union
Journal title: Journal of Geophysical Research: Space Physics
Volume: 120
Issue: 9
Start page: 7642
End page: 7657
Abstract: Recent observations of plasmaspheric hiss emissions by the Van Allen Probes show that broadband hiss emissions in the plasmasphere comprise short-time coherent elements with rising and falling tone frequencies. Based on nonlinear wave growth theory of whistler mode chorus emissions, we have examined the applicability of the nonlinear theory to the coherent hiss emissions. We have generalized the derivation of the optimum wave amplitude for triggering rising tone chorus emissions to the cases of both rising and falling tone hiss elements. The amplitude profiles of the hiss emissions are well approximated by the optimum wave amplitudes for triggering rising or falling tones. Through the formation of electron holes for rising tones and electron hills for falling tones, the coherent waves evolve to attain the optimum amplitudes. An electromagnetic particle simulation confirms the nonlinear wave growth mechanism as the initial phase of the hiss generation process. We find very good agreement between the theoretical optimum amplitudes and the observed amplitudes as a function of instantaneous frequency. We calculate nonlinear growth rates at the equator and find that nonlinear growth rates for rising tone emissions are much larger than the linear growth rates. The time scales of observed hiss emissions also agree with those predicted by the nonlinear theory. Based on the theory, we can infer properties of energetic electrons generating hiss emissions in the equatorial region of the plasmasphere.
Description: Article first published online: 29 SEP 2015
Rights: Accepted for publication in 'Journal of Geophysical Research: Space Physics'. Copyright (year) American Geophysical Union. Further reproduction or electronic distribution is not permitted.
The full-text file will be made open to the public on 29 March 2016 in accordance with publisher's 'Terms and Conditions for Self-Archiving'.
URI: http://hdl.handle.net/2433/203040
DOI(Published Version): 10.1002/2015JA021520
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