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Eriksson, E., Vaivads, A., Alm, L., Graham, D. B., Khotyaintsev, Y. V. & André, M. (2020). Electron acceleration in a magnetotail reconnection outflow region using Magnetospheric MultiScale data. Geophysical Research Letters, 47(1), Article ID e2019GL085080.
Open this publication in new window or tab >>Electron acceleration in a magnetotail reconnection outflow region using Magnetospheric MultiScale data
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2020 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 47, no 1, article id e2019GL085080Article in journal (Refereed) Published
National Category
Fusion, Plasma and Space Physics
Research subject
Physics with specialization in Space and Plasma Physics
Identifiers
urn:nbn:se:uu:diva-359593 (URN)10.1029/2019GL085080 (DOI)000513983400005 ()
Funder
Swedish Research Council, 2013-4309
Available from: 2018-09-06 Created: 2018-09-06 Last updated: 2020-03-23Bibliographically approved
Hamrin, M., Gunell, H., Goncharov, O., De Spiegeleer, A., Fuselier, S., Mukherjee, J., . . . Giles, B. (2019). Can Reconnection be Triggered as a Solar Wind Directional Discontinuity Crosses the Bow Shock?: A Case of Asymmetric Reconnection. Journal of Geophysical Research - Space Physics, 124(11), 8507-8523
Open this publication in new window or tab >>Can Reconnection be Triggered as a Solar Wind Directional Discontinuity Crosses the Bow Shock?: A Case of Asymmetric Reconnection
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2019 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, no 11, p. 8507-8523Article in journal (Refereed) Published
Abstract [en]

Here we present some unique observations of reconnection at a quasi-perpendicular bow shock as an interplanetary directional discontinuity (DD) is crossing it simultaneously with the Magnetospheric Multiscale (MMS) mission. There are no burst data, but available data show indications of ongoing reconnection at the shock southward of MMS: a bifurcated current sheet with signatures of Hall magnetic and electric fields, normal magnetic fields indicating a magnetic connection between the two reconnecting regions, field-aligned currents and electric fields, E . J > 0 indicating a conversion of magnetic to kinetic energy, and subspin resolution ion energy-time spectrograms indicating ions being accelerated away from the X-line. The DD is also observed by four upstream spacecraft (ACE, WIND, Geotail, and ARTEMIS P1) and one downstream in the magnetosheath (Cluster 4), but none of them resolve signatures of ongoing reconnection. We therefore suggest that reconnection was temporarily triggered as the DD was compressed by the shock. Reconnection at the bow shock is inevitably asymmetric with both the density and magnetic field strength being higher on one side of the X-line (magnetosheath side) than on the other side where the plasma flow also is supersonic (solar wind side). This is different from the asymmetry exhibited at the more commonly studied case of asymmetric reconnection at the magnetopause. Asymmetric reconnection of the bow shock type has never been studied before, and the data discussed here present some first indications of the properties of the reconnection region for this type of reconnection.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2019
National Category
Astronomy, Astrophysics and Cosmology Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-406218 (URN)10.1029/2019JA027006 (DOI)000505404700019 ()
Funder
Swedish National Space BoardThe Kempe Foundations
Available from: 2020-03-06 Created: 2020-03-06 Last updated: 2020-03-06Bibliographically approved
Fu, H. S., Cao, J. B., Cao, D., Wang, Z., Vaivads, A., Khotyaintsev, Y. V., . . . Huang, S. Y. (2019). Evidence of Magnetic Nulls in Electron Diffusion Region. Geophysical Research Letters, 46(1), 48-54
Open this publication in new window or tab >>Evidence of Magnetic Nulls in Electron Diffusion Region
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2019 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 1, p. 48-54Article in journal (Refereed) Published
Abstract [en]

Theoretically, magnetic reconnection—the process responsible for solar flares and magnetospheric substorms—occurs at the X‐line or radial null in the electron diffusion region (EDR). However, whether this theory is correct is unknown, because the radial null (X‐line) has never been observed inside the EDR due to the lack of efficient techniques and the scarcity of EDR measurements. Here we report such evidence, using data from the recent MMS mission and the newly developed First‐Order Taylor Expansion (FOTE) Expansion technique. We investigate 12 EDR candidates at the Earth's magnetopause and find radial nulls (X‐lines) in all of them. In some events, spacecraft are only 3 km (one electron inertial length) away from the null. We reconstruct the magnetic topology of these nulls and find it agrees well with theoretical models. These nulls, as reconstructed for the first time inside the EDR by the FOTE technique, indicate that the EDR is active and the reconnection process is ongoing.

Plain Language Summary: Magnetic reconnection is a key process responsible for many explosive phenomena in nature such as solar flares and magnetospheric substorms. Theoretically, such process occurs at the X‐line or radial null in the electron diffusion region (EDR). However, whether this theory is correct is still unknown, because the radial null (X‐line) has never been observed inside the EDR due to the lack of efficient technique and the scarcity of EDR measurements. Here we report such evidence, using data from the recent MMS mission and the newly developed FOTE technique.

Keywords
Electron diffusion region, Magnetic null, Magnetic reconnection, FOTE method, Magnetic topology, Reconstruction
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-377360 (URN)10.1029/2018GL080449 (DOI)000456938600006 ()
Available from: 2019-02-19 Created: 2019-02-19 Last updated: 2019-02-19Bibliographically approved
Cozzani, G., Retino, A., Califano, F., Alexandrova, A., Contel, O. L., Khotyaintsev, Y. V., . . . Burch, J. L. (2019). In situ spacecraft observations of a structured electron diffusion region during magnetopause reconnection. Physical review. E, 99(4), Article ID 043204.
Open this publication in new window or tab >>In situ spacecraft observations of a structured electron diffusion region during magnetopause reconnection
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2019 (English)In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 99, no 4, article id 043204Article in journal (Refereed) Published
Abstract [en]

The electron diffusion region (EDR) is the region where magnetic reconnection is initiated and electrons are energized. Because of experimental difficulties, the structure of the EDR is still poorly understood. A key question is whether the EDR has a homogeneous or patchy structure. Here we report Magnetospheric Multiscale (MMS) spacecraft observations providing evidence of inhomogeneous current densities and energy conversion over a few electron inertial lengths within an EDR at the terrestrial magnetopause, suggesting that the EDR can be rather structured. These inhomogenenities are revealed through multipoint measurements because the spacecraft separation is comparable to a few electron inertial lengths, allowing the entire MMS tetrahedron to be within the EDR most of the time. These observations are consistent with recent high-resolution and low-noise kinetic simulations.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2019
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-382381 (URN)10.1103/PhysRevE.99.043204 (DOI)000463898200002 ()
Available from: 2019-04-25 Created: 2019-04-25 Last updated: 2019-04-25Bibliographically approved
Liu, C., Vaivads, A., Graham, D. B., Khotyaintsev, Y. V., Fu, H. S., Johlander, A., . . . Giles, B. L. (2019). Ion-Beam-Driven Intense Electrostatic Solitary Waves in Reconnection Jet. Geophysical Research Letters, 46(22), 12702-12710
Open this publication in new window or tab >>Ion-Beam-Driven Intense Electrostatic Solitary Waves in Reconnection Jet
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2019 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 22, p. 12702-12710Article in journal (Refereed) Published
Abstract [en]

Electrostatic solitary waves (ESWs) have been reported inside reconnection jets, but their source and role remain unclear hitherto. Here we present the first observational evidence of ESWs generation by cold ion beams inside the jet, by using high-cadence measurements from the Magnetospheric Multiscale spacecraft in the Earth's magnetotail. Inside the jet, intense ESWs with amplitude up to 30 mV m(-1) and potential up to similar to 7% of the electron temperature are observed in association with accelerated cold ion beams. Instability analysis shows that the ion beams are unstable, providing free energy for the ESWs. The waves are observed to thermalize the beams, thus providing a new channel for ion heating inside the jet. Our study suggests that electrostatic turbulence can play an important role in the jet dynamics.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2019
Keywords
reconnection jet, dipolarization front, electrostatic solitary waves, ion beam instability, wave-particle interations, ion heating
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-408233 (URN)10.1029/2019GL085419 (DOI)000498353500001 ()
Available from: 2020-04-06 Created: 2020-04-06 Last updated: 2020-04-06Bibliographically approved
Steinvall, K., Khotyaintsev, Y. V., Graham, D. B., Vaivads, A., Lindqvist, P.-A. -., Russell, C. T. & Burch, J. L. (2019). Multispacecraft Analysis of Electron Holes. Geophysical Research Letters, 46(1), 55-63
Open this publication in new window or tab >>Multispacecraft Analysis of Electron Holes
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2019 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 1, p. 55-63Article in journal (Refereed) Published
Abstract [en]

Electron holes (EHs) are nonlinear electrostatic structures in plasmas. Most previous in situ studies of EHs have been limited to single‐ and two‐spacecraft methods. We present statistics of EHs observed by Magnetospheric Multiscale on the magnetospheric side of the magnetopause during October 2016 when the spacecraft separation was around 6 km. Each EH is observed by all four spacecraft, allowing EH properties to be determined with unprecedented accuracy. We find that the parallel length scale, l, scales with the Debye length. The EHs can be separated into three groups of speed and potential based on their coupling to ions. We present a method for calculating the perpendicular length scale, l. The method can be applied to a small subset of the observed EHs for which we find shapes ranging from almost spherical to more oblate. For the remaining EHs we use statistical arguments to find l/l≈5, implying dominance of oblate EHs.

Plain Language Summary: Electron holes are positively charged structures moving along the magnetic field and are frequently observed in space plasmas in relation to strong currents and electron beams. Electron holes interact with the plasma, leading to electron heating and scattering. In order to understand the effect of these electron holes, we need to accurately determine their properties, such as velocity, length scale, and potential. Most earlier studies have relied on single‐ or two‐spacecraft methods to analyze electron holes. In this study we use the four satellites of the Magnetospheric Multiscale mission to analyze 236 electron holes with unprecedented accuracy. We find that the holes can be divided into three distinct groups with different properties. Additionally, we calculate the width of individual electron holes, finding that they are typically much wider than long, resembling

Keywords
Electron holes
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-377361 (URN)10.1029/2018GL080757 (DOI)000456938600007 ()
Funder
Swedish Research Council, 2016-05507Swedish National Space Board, 2016-05507
Available from: 2019-02-19 Created: 2019-02-19 Last updated: 2019-02-19Bibliographically approved
Fu, H. S., Xu, Y., Vaivads, A. & Khotyaintsev, Y. V. (2019). Super-efficient Electron Acceleration by an Isolated Magnetic Reconnection. Astrophysical Journal Letters, 870(2), Article ID L22.
Open this publication in new window or tab >>Super-efficient Electron Acceleration by an Isolated Magnetic Reconnection
2019 (English)In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 870, no 2, article id L22Article in journal (Refereed) Published
Abstract [en]

Magnetic reconnection-the process typically lasting for a few seconds in space-is able to accelerate electrons. However, the efficiency of the acceleration during such a short period is still a puzzle. Previous analyses, based on spacecraft measurements in the Earth's magnetotail, indicate that magnetic reconnection can enhance electron fluxes up to 100 times. This efficiency is very low, creating an impression that magnetic reconnection is not good at particle acceleration. By analyzing Cluster data, we report here a remarkable magnetic reconnection event during which electron fluxes are enhanced by 10,000 times. Such acceleration, 100 times more efficient than those in previous studies, is caused by the betatron mechanism. Both reconnection fronts and magnetic islands contribute to the acceleration, with the former being more prominent.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
acceleration of particles, magnetic reconnection
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-375876 (URN)10.3847/2041-8213/aafa75 (DOI)000455938700002 ()
Available from: 2019-02-04 Created: 2019-02-04 Last updated: 2019-02-04Bibliographically approved
Eriksson, E., Vaivads, A., Graham, D. B., Divin, A., Khotyaintsev, Y. V., Yordanova, E. & André, M. (2018). Electron Energization at a Reconnecting Magnetosheath Current Sheet [Letter to the editor]. Geophysical Research Letters, 45(16)
Open this publication in new window or tab >>Electron Energization at a Reconnecting Magnetosheath Current Sheet
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2018 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 16Article in journal, Letter (Refereed) Published
Abstract [en]

We present observations of electron energization within a sub-ion-scale magnetosheath current sheet (CS). A number of signatures indicate ongoing reconnection, including the thickness of the CS (∼0.7 ion inertial length), nonzero normal magnetic field, Hall magnetic fields with electrons carrying the Hall currents, and electron heating. We observe localized electron acceleration and heating parallel to the magnetic field at the edges of the CS. Electrostatic waves observed in these regions have low phase velocity and small wave potentials and thus cannot provide the observed acceleration and heating. Instead, we find that the electrons are accelerated by a parallel potential within the separatrix regions. Similar acceleration has been reported based on magnetopause and magnetotail observations.Thus, despite the different plasma conditions in magnetosheath, magnetopause, and magnetotail,the acceleration mechanism and corresponding heating of electrons is similar.

Keywords
magnetic reconnection, magnetosheath, electron heating, electron acceleration, Magnetospheric Multiscale
National Category
Other Physics Topics
Research subject
Physics with specialization in Space and Plasma Physics
Identifiers
urn:nbn:se:uu:diva-359592 (URN)10.1029/2018GL078660 (DOI)000445612500023 ()
Funder
Swedish Research Council, 2013-4309Swedish National Infrastructure for Computing (SNIC), m.2017-1-422Swedish National Infrastructure for Computing (SNIC), m.2016-457
Available from: 2018-09-04 Created: 2018-09-04 Last updated: 2018-10-25Bibliographically approved
Liu, C. M., Fu, H. S., Vaivads, A., Khotyaintsev, Y. V., Gershman, D. J., Hwang, K.-J., . . . Le Contel, O. (2018). Electron Jet Detected by MMS at Dipolarization Front. Geophysical Research Letters, 45(2), 556-564
Open this publication in new window or tab >>Electron Jet Detected by MMS at Dipolarization Front
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2018 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 2, p. 556-564Article in journal (Refereed) Published
Abstract [en]

Using MMS high-resolution measurements, we present the first observation of fast electron jet (V-e similar to 2,000 km/s) at a dipolarization front (DF) in the magnetotail plasma sheet. This jet, with scale comparable to the DF thickness (similar to 0.9 d(i)), is primarily in the tangential plane to the DF current sheet and mainly undergoes the E x B drift motion; it contributes significantly to the current system at the DF, including a localized ring-current that can modify the DF topology. Associated with this fast jet, we observed a persistent normal electric field, strong lower hybrid drift waves, and strong energy conversion at the DF. Such strong energy conversion is primarily attributed to the electron-jet-driven current (E.j(e) approximate to 2 E.j(i)), rather than the ion current suggested in previous studies.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2018
Keywords
electron jet, dipolarization front, electric field, LHD waves, electron current, energy conversion
National Category
Fusion, Plasma and Space Physics Geophysics
Identifiers
urn:nbn:se:uu:diva-347650 (URN)10.1002/2017GL076509 (DOI)000425514300009 ()
Available from: 2018-04-06 Created: 2018-04-06 Last updated: 2018-04-06Bibliographically approved
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
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