Theory and simulation of the generation of whistler‐mode chorus

By Yoshiharu Omura, Yuto Katoh, Danny Summers. 2008

531 citations recorded by the source corpus.

[1] The generation process of whistler-mode chorus emissions is analyzed by both theory and simulation. Driven by an assumed strong temperature anisotropy of energetic electrons, the initial wave growth of chorus is linear. After the linear growth phase, the wave amplitude grows nonlinearly. It is found that the seeds of chorus emissions with rising frequency are generated near the magnetic equator as a result of a nonlinear growth mechanism that depends on the wave amplitude. We derive the relativistic second-order resonance condition for a whistler-mode wave with a varying frequency. Wave trapping of resonant electrons near the equator results in the formation of an electromagnetic electron hole in the wave phase space. For a specific wave phase variation, corresponding to a rising frequency, the electron hole can form a resonant current that causes growth of a wave with a rising frequency. Seeds of chorus elements grow from the saturation level of the whistler-mode instability at the equator and then propagate away from the equator. In the frame of reference moving with the group velocity, the wave frequency is constant. The wave amplitude is amplified by the nonlinear resonant current, which is sustained by the increasing inhomogeneity of the dipole magnetic field over some distance from the equator. Chorus elements are generated successively at the equator so long as a sufficient flux of energetic electrons with a strong temperature anisotropy is present.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/251b9a00e381702d7cd916cdf1ed5a82eb84ec59

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In Astronomy and Astrophysics

1. R. Thorne
2. Wen Li
3. R. Horne
4. Nigel P. Meredith
5. Jacob Bortnik
6. Binbin Ni
7. Y. Shprits
8. Danny Summers

In Nuclear and High Energy Physics

1. R. Thorne
2. Y. Shprits
3. Jacob Bortnik
4. R. Horne
5. Wen Li
6. Binbin Ni
7. Nigel P. Meredith
8. J. Albert

Citations in the corpus

• Nonlinear interaction of radiation belt electrons with electromagnetic ion cyclotron waves (2009, methodology): “Such analysis for test particles has previously been developed and applied to large amplitude whistler mode chorus [e.g., Nunn, 1974; Albert, 2002; Omura et al., 2008; Bortnik et al., 2008].”
• Resonant scattering of plasma sheet electrons leading to diffuse auroral precipitation: 2. Evaluation for whistler mode chorus waves (2011, background): “[6] Nonlinear wave growth theories have also been developed to better understand the generation process and wave characteristics of chorus emissions [e.g., Nunn et al., 1997, 2009; Omura et al., 2008, 2009].”
• Theory and observation of electromagnetic ion cyclotron triggered emissions in the magnetosphere (2010, methodology): “[19] From the analysis of trajectories of resonant ions as described by the second‐order equation, it is found that the maximum value of JE is realized when ∣S∣ = 0.4 [Omura et al., 2008].”
• Wave and particle characteristics of earthward electron injections associated with dipolarization fronts (2010, background): “Self‐consistent numericalstudieshaveshownthatthenonuniformityofthemagnetic field plays a key role in the amplification process of whistler modewaveemissions formedat the equator and that nonlinear effects can increase the frequency of the emissions [ Omura et al., 2008 ].”
• Global model of lower band and upper band chorus from multiple satellite observations (2012, background): “thermal electrons [Katoh and Omura, 2007; Omura et al., 2008; Li et al., 2008, 2009a] injected into the inner magnetosphere during storms and substorms.”
• Time domain structures: What and where they are, what they do, and how they are made (2015, background): “…1967; Morse and Nielson, 1969a, 1969b; Lashmore-Davies and Martin, 1973; Joyce and Hubbard, 1978; Hubbard and Joyce, 1979; Yamamoto and Kan, 1985; Omura et al., 1996, 2008; Berthomier et al., 1998; Miyake et al., 1998; Goldman et al., 1999; Newman et al., 2001; Oppenheim et al., 2001; Singh,…”
• THEMIS analysis of observed equatorial electron distributions responsible for the chorus excitation (2010, background): “... mechanism for upper‐band chorus remains debatable [e.g., Hashimoto and Kimura, 1981; Horne et al., 2003a], it has been generally accepted that lower‐band chorus waves can be generated through a cyclotron resonance with anisotropic electrons with energies between a few and tens of keV [e.g., Kenn”
• Cluster observations of EMIC triggered emissions in association with Pc1 waves near Earth's plasmapause (2010, background): “Omura et al. [2008, 2009] for VLF chorus generation, it is possible for the EMIC triggered emissions to be generated through a nonlinear absolute instability for L‐mode EMIC Figure 2. STAFF‐SC and EFW data from CLUSTER 4 showing the Pc1 waves at ∼ 1.5 Hz and the EMIC triggered emissions rising from”
• Transit time scattering of energetic electrons due to equatorially confined magnetosonic waves (2010, background): “…OF GEOPHYSICAL RESEARCH, VOL. 115, A07213, doi:10.1029/2010JA015283, 2010 A07213 1 of 8 low background magnetic field inhomogeneity [e.g., Omura et al., 2008; Bortnik et al., 2008; Albert and Bortnik, 2009] requires an assessment of whether nonlinear processes might affect the electron…”
• Oblique propagation of whistler mode waves in the chorus source region (2009, methodology): “[43] With respect to the wave-particle interactions involved in the process of generation of chorus [e.g., Trakhtengerts, 1995; Omura et al., 2008], the magnetic equator can be defined as a surface perpendicular to the direction of the geomagnetic field where the magnetic field modulus reaches its…”
• Particle Dynamics in the Earth's Radiation Belts: Review of Current Research and Open Questions (2020, background): “This allows for the possibility of rigorously testing the predictions of different theories of chorus (Omura et al., 2008; Trakhtengerts, 1999).”
• Nonlinear mechanisms of lower-band and upper-band VLF chorus emissions in the magnetosphere (2009, methodology): “[6] Using these parameters, we express the phase velocity and group velocity of the whistler mode wave as [ Omura et al., 2008 ]”
• Modeling the evolution of chorus waves into plasmaspheric hiss (2011, background): “These observations have also been confirmed by numerical simulations that show the development of coherent chorus emissions in near equatorial regions [e.g., Katoh and Omura, 2007; Omura et al., 2008].”