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Abstract Electron cyclotron harmonic waves (ECH) play a key role in scattering and precipitation of plasma sheet electrons. Previous analysis on the resonant interaction between ECH waves and electrons assumed that these waves are generated by a loss cone distribution and propagate nearly perpendicular to the background magnetic field. Recent spacecraft observations, however, have demonstrated that such waves can also be generated by low energy electron beams and propagate at moderately oblique angles . To quantify the effects of this newly observed ECH wave mode on electron dynamics in Earth's magnetosphere, we use quasi‐linear theory to calculate the associated electron pitch angle diffusion coefficient. Utilizing THEMIS spacecraft measurements, we analyze in detail a few representative events of beam‐driven ECH waves in the plasma sheet and the outer radiation belt. Based on the observed wave properties and the hot plasma dispersion relation of these waves, we calculate their bounce‐averaged pitch angle, momentum and mixed diffusion coefficients. We find that these waves most efficiently scatter low‐energy electrons (10–500 eV) toward larger pitch angles, on time scales of to seconds. In contrast, loss‐cone‐driven ECH waves most efficiently scatter higher‐energy electrons (500 eV–5 keV) toward lower pitch‐angles. Importantly, beam‐driven ECH waves can effectively scatter ionospheric electron outflows out of the loss cone near the magnetic equator. As a result, these outflows become trapped in the magnetosphere, forming a near‐field‐aligned anisotropic electron population. Our work highlights the importance of ECH waves, particularly beam‐driven modes, in regulating magnetosphere‐ionosphere particle and energy coupling.
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Electron Acceleration by Quasilinear Processes in the Presence of a Ring-beam Electron Population
A set of self-consistent equations of weak turbulence theory that describe the time evolution of the electron velocity distribution and of the spectra of Langmuir and ion sound waves is solved numerically, considering the presence of a core electron population and a ring-beam electron distribution. The results obtained show that the finite pitch angle of the beam relative to the direction of the ambient magnetic field leads to a spectrum of Langmuir waves which is more complex than the spectrum obtained in the case of beams with zero pitch angle, to an enlarged plateau in the beam region of the electron velocity distribution and to the generation of a prominent high-velocity population in the electron velocity distribution.
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- Award ID(s):
- 2203321
- PAR ID:
- 10494259
- Publisher / Repository:
- Springer Science
- Date Published:
- Journal Name:
- Brazilian Journal of Physics
- Volume:
- 52
- Issue:
- 3
- ISSN:
- 0103-9733
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1007/s13538-022-01085-9
