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Crescent-Shaped Electron Distributions at the Nonreconnecting Magnetopause: Magnetospheric Multiscale Observations
Chinese Acad Sci, State Key Lab Space Weather, Natl Space Sci Ctr, Beijing, Peoples R China.ORCID iD: 0000-0002-9244-1828
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Chinese Acad Sci, State Key Lab Space Weather, Natl Space Sci Ctr, Beijing, Peoples R China.ORCID iD: 0000-0003-1920-2406
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.ORCID iD: 0000-0002-1046-746x
Catholic Univ Amer, Dept Phys, Washington, DC, USA; NASA, Goddard Space Flight Ctr, Greenbelt, MD, USA.ORCID iD: 0000-0001-7088-1059
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2019 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 6, p. 3024-3032Article in journal (Refereed) Published
Abstract [en]

Crescent‐shaped electron distributions perpendicular to the magnetic field are an important indicator of the electron diffusion region in magnetic reconnection. They can be formed by the electron finite gyroradius effect at plasma boundaries or by demagnetized electron motion. In this study, we present Magnetospheric Multiscale mission observations of electron crescents at the flank magnetopause on 20 September 2017, where reconnection signatures are not observed. These agyrotropic electron distributions are generated by electron gyromotion at the thin electron‐scale magnetic boundaries of a magnetic minimum after magnetic curvature scattering. The variation of their angular range in the perpendicular plane is in good agreement with predictions. Upper hybrid waves are observed to accompany the electron crescents at all four Magnetospheric Multiscale spacecraft as a result of the beam‐plasma instability associated with these agyrotropic electron distributions. This study suggests electron crescents can be more frequently formed at the magnetopause.

Abstract [en]

Plain Language Summary

In this study, we present Magnetospheric Multiscale mission observations of electron crescents at the flank magnetopause and these agyrotropic electron distributions are formed at thin electron‐scale magnetic boundaries after electron pitch angle scattering by the curved magnetic field. These results suggest that agyrotropic electron distributions can be more frequently formed at the magnetopause: (1) magnetic reconnection is not necessary, although electron crescents are taken as one of the observational signatures of the electron diffusion region, and (2) agyrotropic electron distributions can cover a large local time range to the flank magnetopause. In addition, upper hybrid waves accompanied with the electron crescents are observed as a result of the beam‐plasma interaction associated with these agyrotropic electron distributions. This suggests that high‐frequency waves play a role in electron dynamics through wave‐particle interactions.

Place, publisher, year, edition, pages
2019. Vol. 46, no 6, p. 3024-3032
Keywords [en]
agyrotropic electron distributions, electron finite gyroradius effect, upper hybrid waves
National Category
Fusion, Plasma and Space Physics Geophysics
Identifiers
URN: urn:nbn:se:uu:diva-382993DOI: 10.1029/2019GL082231ISI: 000464650400002OAI: oai:DiVA.org:uu-382993DiVA, id: diva2:1315255
Available from: 2019-05-13 Created: 2019-05-13 Last updated: 2019-05-13Bibliographically approved

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Li, WenyaGraham, Daniel B.Khotyaintsev, Yu. V.Lindqvist, P. A.

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Tang, B. -BLi, WenyaGraham, Daniel B.Rager, A. C.Wang, C.Khotyaintsev, Yu. V.Lavraud, B.Hasegawa, H.Zhang, Y. -CDai, L.Giles, B. L.Russell, C. T.Lindqvist, P. A.Ergun, R. E.
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Swedish Institute of Space Physics, Uppsala Division
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Geophysical Research Letters
Fusion, Plasma and Space PhysicsGeophysics

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