Saturation mechanisms of whistler-mode chorus emissions in the inner magnetosphere

Details Saturation mechanisms of whistler-mode chorus emissions in the inner magnetosphere Saturation mechanisms of whistler-mode chorus emissions in the inner magnetosphere

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsm22a..03o&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #SM22A-03

Physics

Plasma Physics

[2774] Magnetospheric Physics / Radiation Belts, [7829] Space Plasma Physics / Kinetic Waves And Instabilities, [7839] Space Plasma Physics / Nonlinear Phenomena, [7867] Space Plasma Physics / Wave/Particle Interactions

Scientific paper

Recent particle simulation studies[1,2] reveal that seeds of whistler-mode chorus emissions are generated as a result of the absolute instability of the nonlinear wave growth near the equator. The nonlinear wave growth is due to formation of an electromagnetic electron hole in the velocity phase space. The rising tone of chorus emissions is a key element causing the nonlinear wave growth near the equator where the inhomogeneity of the magnetic field is negligible. The frequency sweep rate is proportional to the wave amplitude, while the gain of the absolute instability is relatively small because of the balance between the nonlinear growth term and the convection term of the wave amplitude equation. The absolute instability at the equator is saturated because of filling of the electron hole due to entrapping of resonant electrons by the chorus wave packet propagating away from the equator. The chorus wave packet grows in space due to the convective instability driven by the electron hole. As the wave packet propagates away from the equator, the resonance velocity increases while the parallel velocities of the resonant electrons decrease due to the adiabatic motion in the dipole magnetic field. The adiabatic variation of the energetic electron flux results in saturation of the nonlinear convective instability. Using the optimum wave amplitude for triggering the rising tone emission [3], we evaluate the maximum wave amplitude attainable through both absolute and convective instabilities of chorus wave packets for various parameters in the inner magnetosphere. [1] Hikishima, M., Y. Omura, and D. Summers (2010), Self-consistent particle simulation of whistler mode triggered emissions, J. Geophys. Res., 115, A12246, doi:10.1029/2010JA015860. [2] Katoh, Y., and Y. Omura (2011), Amplitude dependence of frequency sweep rates of whistler mode chorus emissions, J. Geophys. Res., 116, A07201, doi:10.1029/2011JA016496. [3] Omura, Y., and D. Nunn (2011), Triggering process of whistler mode chorus emissions in the magnetosphere, J. Geophys. Res., 116, A05205,doi:10.1029/2010JA016280.

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