Oblique Instability of Quasi-Parallel Whistler Waves in the Presence of Cold and Warm Electron Populations
Whistler waves propagating nearly parallel to the ambient magnetic field experience a nonlinear instability that generates oblique electrostatic waves, including whistlers near the resonance cone that resemble oblique chorus in the Earth's magnetosphere. Focusing on the generation of oblique wh...
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Main Authors | , , |
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Format | Journal Article |
Language | English |
Published |
28.06.2024
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Subjects | |
Online Access | Get full text |
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Summary: | Whistler waves propagating nearly parallel to the ambient magnetic field
experience a nonlinear instability that generates oblique electrostatic waves,
including whistlers near the resonance cone that resemble oblique chorus in the
Earth's magnetosphere. Focusing on the generation of oblique whistlers, earlier
analysis of the instability is extended to the case where low-energy background
plasma consists of both a "cold" population with energy ~ eV and a "warm"
electron component with energy ~100 eV. This is motivated by observations in
the Earth's magnetosphere where oblique chorus waves were shown to interact
resonantly with the warm electrons. The main results are: i) the instability
producing oblique whistlers is sensitive to the shape of the electron
distribution at low energies. In the whistler range of frequencies, two
distinct peaks in the growth rate are typically present: one at low wavenumbers
associated with the warm population and one at high wavenumbers associated with
the cold population; ii) the instability producing oblique whistler waves
persists in cases where the temperature of the cold population is relatively
high, including cases where cold population is absent and only the warm
population is included; iii) particle-in-cell simulations show that the
instability leads to heating of the background plasma and formation of
characteristic resonant plateau and beam features in the electron distribution.
The plateau/beam features have been previously detected in spacecraft
observations of oblique chorus waves. However, they were attributed to external
sources and were proposed to be the mechanism generating oblique chorus. In the
present scenario, the causality link is reversed: the instability generating
oblique whistler waves is shown to be a possible mechanism to generate the
plateau/beam features. |
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DOI: | 10.48550/arxiv.2406.19818 |