Generation of Highly Oblique Lower Band Chorus Via Nonlinear Three-Wave Resonance
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- New Mexico Consortium, Los Alamos, NM (United States)
- Space Science Institute, Boulder, CO (United States)
- New Mexico Consortium, Los Alamos, NM (United States); Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Chorus in the inner magnetosphere has been observed frequently at geomagnetically active times, typically exhibiting a two-band structure with a quasi-parallel lower band and an upper band with a broad range of wave normal angles. But recent observations by Van Allen Probes confirm another type of lower band chorus, which has a large wave normal angle close to the resonance cone angle. It has been proposed that these waves could be generated by a low-energy beam-like electron component or by temperature anisotropy of keV electrons in the presence of a low-energy plateau-like electron component. This paper, however, presents an alternative mechanism for generation of this highly oblique lower band chorus. Through a nonlinear three-wave resonance, a quasi-parallel lower band chorus wave can interact with a mildly oblique upper band chorus wave, producing a highly oblique quasi-electrostatic lower band chorus wave. This theoretical analysis is confirmed by 2-D electromagnetic particle-in-cell simulations. Furthermore, as the newly generated waves propagate away from the equator, their wave normal angle can further increase and they are able to scatter low-energy electrons to form a plateau-like structure in the parallel velocity distribution. As a result, the three-wave resonance mechanism may also explain the generation of quasi-parallel upper band chorus which has also been observed in the magnetosphere.
- Research Organization:
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
- Sponsoring Organization:
- National Aeronautics and Space Administration (NASA); USDOE
- Grant/Contract Number:
- AC52-06NA25396
- OSTI ID:
- 1415428
- Report Number(s):
- LA-UR-17-30358; TRN: US1800821
- Journal Information:
- Geophysical Research Letters, Vol. 44, Issue 19; ISSN 0094-8276
- Publisher:
- American Geophysical UnionCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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Observation of Oblique Lower Band Chorus Generated by Nonlinear Three-Wave Interaction
The relationship between the macroscopic state of electrons and the properties of chorus waves observed by the Van Allen Probes