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Tang, B.-B. -., Li, W., Graham, D. B., Rager, A. C., Wang, C., Khotyaintsev, Y. V. V., . . . Burch, J. L. (2019). Crescent-Shaped Electron Distributions at the Nonreconnecting Magnetopause: Magnetospheric Multiscale Observations. Geophysical Research Letters, 46(6), 3024-3032
Open this publication in new window or tab >>Crescent-Shaped Electron Distributions at the Nonreconnecting Magnetopause: Magnetospheric Multiscale Observations
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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.

Keywords
agyrotropic electron distributions, electron finite gyroradius effect, upper hybrid waves
National Category
Fusion, Plasma and Space Physics Geophysics
Identifiers
urn:nbn:se:uu:diva-382993 (URN)10.1029/2019GL082231 (DOI)000464650400002 ()
Available from: 2019-05-13 Created: 2019-05-13 Last updated: 2019-12-11Bibliographically approved
Gingell, I., Schwartz, S. J., Eastwood, J. P., Burch, J. L., Ergun, R. E., Fuselier, S., . . . Wilder, F. (2019). Observations of Magnetic Reconnection in the Transition Region of Quasi-Parallel Shocks. Geophysical Research Letters, 46(3), 1177-1184
Open this publication in new window or tab >>Observations of Magnetic Reconnection in the Transition Region of Quasi-Parallel Shocks
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2019 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 3, p. 1177-1184Article in journal (Refereed) Published
Abstract [en]

Using observations of Earth's bow shock by the Magnetospheric Multiscale mission, we show for the first time that active magnetic reconnection is occurring at current sheets embedded within the quasi-parallel shock's transition layer. We observe an electron jet and heating but no ion response, suggesting we have observed an electron-only mode. The lack of ion response is consistent with simulations showing reconnection onset on sub-ion time scales. We also discuss the impact of electron heating in shocks via reconnection.

National Category
Geophysics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-381842 (URN)10.1029/2018GL081804 (DOI)000462072800007 ()
Available from: 2019-04-15 Created: 2019-04-15 Last updated: 2019-12-11Bibliographically approved
Farrugia, C. J., Cohen, I. J., Vasquez, B. J., Lugaz, N., Alm, L., Torbert, R. B., . . . Pollock, C. J. (2018). Effects in the Near-Magnetopause Magnetosheath Elicited by Large-Amplitube Alfvenic Fluctuations Terminating in a Field and Flow Discontinuity. Journal of Geophysical Research - Space Physics, 123(11), 8983-9004
Open this publication in new window or tab >>Effects in the Near-Magnetopause Magnetosheath Elicited by Large-Amplitube Alfvenic Fluctuations Terminating in a Field and Flow Discontinuity
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2018 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 11, p. 8983-9004Article in journal (Refereed) Published
Abstract [en]

In this paper we report on a sequence of large-amplitude Alfvenic fluctuations terminating in a field and flow discontinuity and their effects on electromagnetic fields and plasmas in the near-magnetopause magnetosheath. An arc-polarized structure in the magnetic field was observed by the Time History of Events and Macroscale Interactions during Substorms-C in the solar wind, indicative of nonlinear Alfven waves. It ends with a combined tangential discontinuity/vortex sheet, which is strongly inclined to the ecliptic plane and at which there is a sharp rise in the density and a drop in temperature. Several effects resulting from this structure were observed by the Magnetospheric Multiscale spacecraft in the magnetosheath close to the subsolar point (11:30 magnetic local time) and somewhat south of the geomagnetic equator (-33 degrees magnetic latitude): (i) kinetic Alfven waves; (ii) a peaking of the electric and magnetic field strengths where E . J becomes strong and negative (-1 nW/m(3)) just prior to an abrupt dropout of the fields; (iii) evolution in the pitch angle distribution of energetic (a few tens of kilo-electron-volts) ions (H+, Hen+, and On+) and electrons inside a high-density region, which we attribute to gyrosounding of the tangential discontinuity/vortex sheet structure passing by the spacecraft; (iv) field-aligned acceleration of ions and electrons that could be associated with localized magnetosheath reconnection inside the high-density region; and (v) variable and strong flow changes, which we argue to be unrelated to reconnection at partial magnetopause crossings and likely result from deflections of magnetosheath flow by a locally deformed, oscillating magnetopause.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2018
National Category
Fusion, Plasma and Space Physics Geophysics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-372831 (URN)10.1029/2018JA025724 (DOI)000453227400007 ()
Available from: 2019-01-09 Created: 2019-01-09 Last updated: 2019-12-12Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-5617-9765

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