Whistler Waves Associated With Electron Beams in Magnetopause Reconnection Diffusion Regions
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- Astronomy Department University of Maryland College Park MD USA, NASA Goddard Space Flight Center Greenbelt MD USA
- Swedish Institute of Space Physics Uppsala Sweden
- Laboratoire de Physique des Plasmas CNRS/Sorbonne Université/Université Paris‐Saclay/Observatoire de Paris/ Ecole Polytechnique Institut Polytechnique de Paris Paris France
- Department of Physics University of Texas at Arlington Arlington TX USA
- Earth, Oceans, and Space Science Southwest Research Institute Durham NH USA
- Institut de Recherche en Astrophysique et Planétologie Université de Toulouse Toulouse France, Centre National de la Recherche Scientifique Toulouse France
- Southwest Research Institute San Antonio San Antonio TX USA
Abstract Whistler waves are often observed in magnetopause reconnection associated with electron beams. We analyze seven MMS crossings surrounding the electron diffusion region (EDR) to study the role of electron beams in whistler excitation. Waves have two major types: (a) Narrow‐band waves with high ellipticities and (b) broad‐band waves that are more electrostatic with significant variations in ellipticities and wave normal angles. While both types of waves are associated with electron beams, the key difference is the anisotropy of the background population, with perpendicular and parallel anisotropies, respectively. The linear instability analysis suggests that the first type of wave is mainly due to the background anisotropy, with the beam contributing additional cyclotron resonance to enhance the wave growth. The second type of broadband waves are excited via Landau resonance, and as seen in one event, the beam anisotropy induces an additional cyclotron mode. The results are supported by particle‐in‐cell simulations. We infer that the first type occurs downstream of the central EDR, where background electrons experience Betatron acceleration to form the perpendicular anisotropy; the second type occurs in the central EDR of guide field reconnection. A parametric study is conducted with linear instability analysis. A beam anisotropy alone of above ∼3 likely excites the cyclotron mode waves. Large beam drifts cause Doppler shifts and may lead to left‐hand polarizations in the ion frame. Future studies are needed to determine whether the observation covers a broader parameter regime and to understand the competition between whistler and other instabilities.
- Research Organization:
- Univ. of Maryland, College Park, MD (United States)
- Sponsoring Organization:
- National Aeronautics and Space Administration (NASA); National Science Foundation (NSF); USDOE; USDOE Office of Science (SC)
- Grant/Contract Number:
- SC0016278
- OSTI ID:
- 1888317
- Journal Information:
- Journal of Geophysical Research. Space Physics, Journal Name: Journal of Geophysical Research. Space Physics Journal Issue: 9 Vol. 127; ISSN 2169-9380
- Publisher:
- American Geophysical Union (AGU)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
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