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Publications (10 of 16) Show all publications
Norgren, C., Graham, D. B., Khotyaintsev, Y. V., André, M., Vaivads, A., Hesse, M., . . . Russell, C. T. (2018). Electron Reconnection in the Magnetopause Current Layer. Journal of Geophysical Research - Space Physics, 123(11), 9222-9238
Open this publication in new window or tab >>Electron Reconnection in the Magnetopause Current Layer
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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. 9222-9238Article in journal (Refereed) Published
Abstract [en]

The electron dynamics within thin current sheets plays a key role both for the process of magnetic reconnection and other energy transfer mechanisms but, from an observational point of view, is not well understood. In this paper we report observations of a reconnecting current sheet with intermediate guide field B-G = 0.5B(in), where B-in is the magnetic field amplitude in the inflow regions. The current sheet width is comparable to electron spatial scales. It shows a bifurcated structure and is embedded within the magnetopause current layer with thickness of several ion scales. The electron scale current sheet has strong out-of-plane and in-plane currents, Hall electric and magnetic fields, a finite magnetic field component normal to the current sheet, and nongyrotropic electron distributions formed due to finite gyroradius effects at the boundary of the current sheet. Comparison between test particle simulations and electron data shows that electrons approaching from the edge of the largest magnetic curvature are scattered to perpendicular pitch angles in the center of the current sheet while electrons entering from the opposite side remain close to field aligned. The comparison also shows that an observed depletion in phase space at antiparallel pitch angles can be explained if an out-of-plane electric field, which due to the guide field is close to antiparallel to the magnetic field, is present in the center of the current sheet. This electric field would be consistent with the reconnection electric field, and we therefore interpret the depletion of electron phase space density as a manifestation of ongoing reconnection.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2018
National Category
Geophysics Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-372832 (URN)10.1029/2018JA025676 (DOI)000453227400022 ()
Available from: 2019-01-09 Created: 2019-01-09 Last updated: 2019-01-09Bibliographically approved
Li, W. Y., André, M., Khotyaintsev, Y. V., Vaivads, A., Fuselier, S. A., Graham, D. B., . . . Burch, J. (2017). Cold Ionospheric Ions in the Magnetic Reconnection Outflow Region. Journal of Geophysical Research - Space Physics, 122(10), 10194-10202
Open this publication in new window or tab >>Cold Ionospheric Ions in the Magnetic Reconnection Outflow Region
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2017 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 10, p. 10194-10202Article in journal (Refereed) Published
Abstract [en]

Magnetosheath plasma usually determines properties of asymmetric magnetic reconnection at the subsolar region of Earth's magnetopause. However, cold plasma that originated from the ionosphere can also reach the magnetopause and modify the kinetic physics of asymmetric reconnection. We present a magnetopause crossing with high-density (10-60 cm(-3)) cold ions and ongoing reconnection from the observation of the Magnetospheric Multiscale (MMS) spacecraft. The magnetopause crossing is estimated to be 300 ion inertial lengths south of the X line. Two distinct ion populations are observed on the magnetosheath edge of the ion jet. One population with high parallel velocities (200-300 km/s) is identified to be cold ion beams, and the other population is the magnetosheath ions. In the deHoffman-Teller frame, the field-aligned magnetosheath ions are Alfvenic and move toward the jet region, while the field-aligned cold ion beams move toward the magnetosheath boundary layer, with much lower speeds. These cold ion beams are suggested to be from the cold ions entering the jet close to the X line. This is the first observation of the cold ionospheric ions in the reconnection outflow region, including the reconnection jet and the magnetosheath boundary layer.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2017
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-342096 (URN)10.1002/2017JA024287 (DOI)000419937800031 ()
Available from: 2018-03-02 Created: 2018-03-02 Last updated: 2018-03-02Bibliographically approved
Graham, D. B., Khotyaintsev, Y. V., Vaivads, A., Norgren, C., André, M., Webster, J. M., . . . Russell, C. T. (2017). Instability of Agyrotropic Electron Beams near the Electron Diffusion Region. Physical Review Letters, 119(2), Article ID 025101.
Open this publication in new window or tab >>Instability of Agyrotropic Electron Beams near the Electron Diffusion Region
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2017 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 119, no 2, article id 025101Article in journal (Refereed) Published
Abstract [en]

During a magnetopause crossing the Magnetospheric Multiscale spacecraft encountered an electron diffusion region (EDR) of asymmetric reconnection. The EDR is characterized by agyrotropic beam and crescent electron distributions perpendicular to the magnetic field. Intense upper-hybrid (UH) waves are found at the boundary between the EDR and magnetosheath inflow region. The UH waves are generated by the agyrotropic electron beams. The UH waves are sufficiently large to contribute to electron diffusion and scattering, and are a potential source of radio emission near the EDR. These results provide observational evidence of wave-particle interactions at an EDR, and suggest that waves play an important role in determining the electron dynamics.

National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-361237 (URN)10.1103/PhysRevLett.119.025101 (DOI)000405367800008 ()28753352 (PubMedID)
Funder
Swedish National Space Board, 175/15
Available from: 2018-09-26 Created: 2018-09-26 Last updated: 2018-09-26Bibliographically approved
Fuselier, S. A., Vines, S. K., Burch, J. L., Petrinec, S. M., Trattner, K. J., Cassak, P. A., . . . Webster, J. M. (2017). Large-scale characteristics of reconnection diffusion regions and associated magnetopause crossings observed by MMS. Journal of Geophysical Research - Space Physics, 122(5), 5466-5486
Open this publication in new window or tab >>Large-scale characteristics of reconnection diffusion regions and associated magnetopause crossings observed by MMS
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2017 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 5, p. 5466-5486Article in journal (Refereed) Published
Abstract [en]

The Magnetospheric Multiscale (MMS) mission was designed to make observations in the very small electron diffusion region (EDR), where magnetic reconnection takes place. From a data set of over 4500 magnetopause crossings obtained in the first phase of the mission, MMS had encounters near or within 12 EDRs. These 12 events and associated magnetopause crossings are considered as a group to determine if they span the widest possible range of external and internal conditions (i.e., in the solar wind and magnetosphere). In addition, observations from MMS are used to determine if there are multiple X-lines present and also to provide information on X-line location relative to the spacecraft. These 12 events represent nearly the widest possible range of conditions at the dayside magnetopause. They occur over a wide range of local times and magnetic shear angles between the magnetosheath and magnetospheric magnetic fields. Most show evidence for multiple reconnection sites.

National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-329112 (URN)10.1002/2017JA024024 (DOI)000403912500041 ()
Available from: 2017-10-19 Created: 2017-10-19 Last updated: 2017-10-24Bibliographically approved
André, M., Odelstad, E., Graham, D. B., Eriksson, A. I., Karlsson, T., Wieser, G. S., . . . Richter, I. (2017). Lower hybrid waves at comet 67P/Churyumov-Gerasimenko. Paper presented at International Conference on Cometary Science - Comets - A New Vision after Rosetta and Philae, NOV 14-18, 2016, Toulouse, FRANCE. Monthly notices of the Royal Astronomical Society, 469, S29-S38
Open this publication in new window or tab >>Lower hybrid waves at comet 67P/Churyumov-Gerasimenko
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2017 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 469, p. S29-S38Article in journal (Refereed) Published
Abstract [en]

We investigate the generation of waves in the lower hybrid frequency range by density gradients in the near plasma environment of comet 67P/Churyumov-Gerasimenko. When the plasma is dominated by water ions from the comet, a situation with magnetized electrons and unmagnetized ions is favourable for the generation of lower hybrid waves. These waves can transfer energy between ions and electrons and reshape the plasma environment of the comet. We consider cometocentric distances out to a few hundred km. We find that when the electron motion is not significantly interrupted by collisions with neutrals, large average gradients within tens of km of the comet, as well as often observed local large density gradients at larger distances, are often likely to be favourable for the generation of lower hybrid waves. Overall, we find that waves in the lower hybrid frequency range are likely to be common in the near plasma environment.

Place, publisher, year, edition, pages
OXFORD UNIV PRESS, 2017
Keywords
plasmas, waves, comets: general
National Category
Fusion, Plasma and Space Physics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-376682 (URN)10.1093/mnras/stx868 (DOI)000443940500003 ()
Conference
International Conference on Cometary Science - Comets - A New Vision after Rosetta and Philae, NOV 14-18, 2016, Toulouse, FRANCE
Available from: 2019-02-15 Created: 2019-02-15 Last updated: 2019-02-15Bibliographically approved
Graham, D. B., Khotyaintsev, Y. V., Norgren, C., Vaivads, A., André, M., Toledo-Redondo, S., . . . Burch, J. L. (2017). Lower hybrid waves in the ion diffusion and magnetospheric inflow regions. Journal of Geophysical Research - Space Physics, 122(1), 517-533
Open this publication in new window or tab >>Lower hybrid waves in the ion diffusion and magnetospheric inflow regions
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2017 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 1, p. 517-533Article in journal (Refereed) Published
Abstract [en]

The role and properties of lower hybrid waves in the ion diffusion region and magnetospheric inflow region of asymmetric reconnection are investigated using the Magnetospheric Multiscale (MMS) mission. Two distinct groups of lower hybrid waves are observed in the ion diffusion region and magnetospheric inflow region, which have distinct properties and propagate in opposite directions along the magnetopause. One group develops near the ion edge in the magnetospheric inflow, where magnetosheath ions enter the magnetosphere through the finite gyroradius effect and are driven by the ion-ion cross-field instability due to the interaction between the magnetosheath ions and cold magnetospheric ions. This leads to heating of the cold magnetospheric ions. The second group develops at the sharpest density gradient, where the Hall electric field is observed and is driven by the lower hybrid drift instability. These drift waves produce cross-field particle diffusion, enabling magnetosheath electrons to enter the magnetospheric inflow region thereby broadening the density gradient in the ion diffusion region.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2017
Keywords
Magnetic reconnection, Ion diffusion region, Lower hybrid waves
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-319788 (URN)10.1002/2016JA023572 (DOI)000395655800038 ()
Funder
Swedish National Space Board
Available from: 2017-04-12 Created: 2017-04-12 Last updated: 2017-11-29Bibliographically approved
Voros, Z., Yordanova, E., Varsani, A., Genestreti, K. J., Khotyaintsev, Y. V., Li, W., . . . Saito, Y. (2017). MMS Observation of Magnetic Reconnection in the Turbulent Magnetosheath. Journal of Geophysical Research - Space Physics, 122(11), 11442-11467
Open this publication in new window or tab >>MMS Observation of Magnetic Reconnection in the Turbulent Magnetosheath
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2017 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 11, p. 11442-11467Article in journal (Refereed) Published
Abstract [en]

In this paper we use the full armament of the MMS (Magnetospheric Multiscale) spacecraft to study magnetic reconnection in the turbulent magnetosheath downstream of a quasi-parallel bow shock. Contrarily to the magnetopause and magnetotail cases, only a few observations of reconnection in the magnetosheath have been reported. The case study in this paper presents, for the first time, both fluid-scale and kinetic-scale signatures of an ongoing reconnection in the turbulent magnetosheath. The spacecraft are crossing the reconnection inflow and outflow regions and the ion diffusion region (IDR). Inside the reconnection outflows D shape ion distributions are observed. Inside the IDR mixing of ion populations, crescent-like velocity distributions and ion accelerations are observed. One of the spacecraft skims the outer region of the electron diffusion region, where parallel electric fields, energy dissipation/conversion, electron pressure tensor agyrotropy, electron temperature anisotropy, and electron accelerations are observed. Some of the difficulties of the observations of magnetic reconnection in turbulent plasma are also outlined.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2017
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-342091 (URN)10.1002/2017JA024535 (DOI)000419938600034 ()
Available from: 2018-03-01 Created: 2018-03-01 Last updated: 2019-11-22Bibliographically approved
Graham, D. B., Khotyaintsev, Y. V., Norgren, C., Vaivads, A., André, M., Lindqvist, P.-A. -., . . . Burch, J. L. (2016). Electron currents and heating in the ion diffusion region of asymmetric reconnection. Geophysical Research Letters, 43(10), 4691-4700
Open this publication in new window or tab >>Electron currents and heating in the ion diffusion region of asymmetric reconnection
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2016 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, no 10, p. 4691-4700Article in journal (Refereed) Published
Abstract [en]

In this letter the structure of the ion diffusion region of magnetic reconnection at Earth's magnetopause is investigated using the Magnetospheric Multiscale (MMS) spacecraft. The ion diffusion region is characterized by a strong DC electric field, approximately equal to the Hall electric field, intense currents, and electron heating parallel to the background magnetic field. Current structures well below ion spatial scales are resolved, and the electron motion associated with lower hybrid drift waves is shown to contribute significantly to the total current density. The electron heating is shown to be consistent with large-scale parallel electric fields trapping and accelerating electrons, rather than wave-particle interactions. These results show that sub-ion scale processes occur in the ion diffusion region and are important for understanding electron heating and acceleration.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-299741 (URN)10.1002/2016GL068613 (DOI)000378347500004 ()
Funder
Swedish National Space Board
Available from: 2016-07-26 Created: 2016-07-26 Last updated: 2017-11-28Bibliographically approved
Khotyaintsev, Y. V., Graham, D. B., Norgren, C., Eriksson, E., Li, W., Johlander, A., . . . Burch, J. L. (2016). Electron jet of asymmetric reconnection. Geophysical Research Letters, 43(11), 5571-5580
Open this publication in new window or tab >>Electron jet of asymmetric reconnection
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2016 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, no 11, p. 5571-5580Article in journal (Refereed) Published
Abstract [en]

We present Magnetospheric Multiscale observations of an electron-scale current sheet and electron outflow jet for asymmetric reconnection with guide field at the subsolar magnetopause. The electron jet observed within the reconnection region has an electron Mach number of 0.35 and is associated with electron agyrotropy. The jet is unstable to an electrostatic instability which generates intense waves with E-vertical bar amplitudes reaching up to 300mVm(-1) and potentials up to 20% of the electron thermal energy. We see evidence of interaction between the waves and the electron beam, leading to quick thermalization of the beam and stabilization of the instability. The wave phase speed is comparable to the ion thermal speed, suggesting that the instability is of Buneman type, and therefore introduces electron-ion drag and leads to braking of the electron flow. Our observations demonstrate that electrostatic turbulence plays an important role in the electron-scale physics of asymmetric reconnection.

Keywords
magnetic reconnection, diffusion region, electron dynamics, lower hybrid waves, Buneman instability
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-301043 (URN)10.1002/2016GL069064 (DOI)000379851800005 ()
Funder
Swedish National Space Board, 139/12, 175/15
Available from: 2016-08-18 Created: 2016-08-17 Last updated: 2017-11-28Bibliographically approved
Norgren, C., Graham, D. B., Khotyaintsev, Y. V., André, M., Vaivads, A., Chen, L.-J. -., . . . Burch, J. L. (2016). Finite gyroradius effects in the electron outflow of asymmetric magnetic reconnection. Geophysical Research Letters, 43(13), 6724-6733
Open this publication in new window or tab >>Finite gyroradius effects in the electron outflow of asymmetric magnetic reconnection
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2016 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, no 13, p. 6724-6733Article in journal (Refereed) Published
Abstract [en]

We present observations of asymmetric magnetic reconnection showing evidence of electron demagnetization in the electron outflow. The observations were made at the magnetopause by the four Magnetospheric Multiscale (MMS) spacecraft, separated by approximate to 15km. The reconnecting current sheet has negligible guide field, and all four spacecraft likely pass close to the electron diffusion region just south of the X line. In the electron outflow near the X line, all four spacecraft observe highly structured electron distributions in a region comparable to a few electron gyroradii. The distributions consist of a core with T-vertical bar>T and a nongyrotropic crescent perpendicular to the magnetic field. The crescents are associated with finite gyroradius effects of partly demagnetized electrons. These observations clearly demonstrate the manifestation of finite gyroradius effects in an electron-scale reconnection current sheet.

Keywords
magnetic reconnection, electron demagnetization, finite gyroradius effects, electron diffusion region
National Category
Geophysics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-304453 (URN)10.1002/2016GL069205 (DOI)000380901600006 ()
Funder
Swedish National Space Board, 23/12:2 175/15
Available from: 2016-10-05 Created: 2016-10-05 Last updated: 2017-11-30Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-6561-2337

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