Journal article
Nonlinear wave growth theory of coherent hiss emissions in the plasmasphere
Journal of geophysical research. Space physics, Vol.120(9), pp.7642-7657
09/2015
DOI: 10.1002/2015JA021520
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.
Key Points
Nonlinear theory of chorus waves can explain observations of coherent hiss emissions
Optimum wave amplitudes for triggering rising and falling tone emissions are derived
Upper limit of hiss is determined by optimum and threshold amplitudes for rising tones
Details
- Title: Subtitle
- Nonlinear wave growth theory of coherent hiss emissions in the plasmasphere
- Creators
- Yoshiharu Omura - Kyoto UniversitySatoko Nakamura - Kyoto UniversityCraig A Kletzing - University of IowaDanny Summers - Kyoto UniversityMitsuru Hikishima - Nagoya University
- Resource Type
- Journal article
- Publication Details
- Journal of geophysical research. Space physics, Vol.120(9), pp.7642-7657
- DOI
- 10.1002/2015JA021520
- ISSN
- 2169-9380
- eISSN
- 2169-9402
- Number of pages
- 16
- Grant note
- JSPS KAKENHI (26287120 and 15K17771)
- Language
- English
- Date published
- 09/2015
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984199822002771
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