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Khotyaintsev, Y. V., Graham, D. B., Norgren, C. & Vaivads, A. (2019). Collisionless Magnetic Reconnection and Waves: Progress Review. FRONTIERS IN ASTRONOMY AND SPACE SCIENCES, 6, Article ID 70.
Open this publication in new window or tab >>Collisionless Magnetic Reconnection and Waves: Progress Review
2019 (English)In: FRONTIERS IN ASTRONOMY AND SPACE SCIENCES, ISSN 2296-987X, Vol. 6, article id 70Article, review/survey (Refereed) Published
Abstract [en]

Magnetic reconnection is a fundamental process whereby microscopic plasma processes cause macroscopic changes in magnetic field topology, leading to explosive energy release. Waves and turbulence generated during the reconnection process can produce particle diffusion and anomalous resistivity, as well as heat the plasma and accelerate plasma particles, all of which can impact the reconnection process. We review progress on waves related to reconnection achieved using high resolution multi-point in situ observations over the last decade, since early Cluster and THEMIS observations and ending with recent Magnetospheric Multiscale results. In particular, we focus on the waves most frequently observed in relation to reconnection, ranging from low-frequency kinetic Alfven waves (KAW), to intermediate frequency lower hybrid and whistler-mode waves, electrostatic broadband and solitary waves, as well as the high-frequency upper hybrid, Langmuir, and electron Bernstein waves. Significant progress has been made in understanding localization of the different wave modes in the context of the reconnection picture, better quantification of generation mechanisms and wave-particle interactions, including anomalous resistivity. Examples include: temperature anisotropy driven whistlers in the flux pileup region, anomalous effects due to lower-hybrid waves, upper hybrid wave generation within the electron diffusion region, wave-particle interaction of electrostatic solitary waves. While being clearly identified in observations, some of the wave processes remain challenging for reconnection simulations (electron Bernstein, upper hybrid, Langmuir, whistler), as the instabilities (streaming, loss-cone, shell) which drive these waves require high resolution of distribution functions in phase space, and realistic ratio of Debye to electron inertia scales. We discuss how reconnection configuration, i.e., symmetric vs. asymmetric, guide-field vs. antiparallel, affect wave occurrence, generation, effect on particles, and feedback on the overall reconnection process. Finally, we outline some of the major open questions, such as generation of electromagnetic radiation by reconnection sites and role of waves in triggering/onset of reconnection.

Keywords
magnetic reconnection, turbulence, waves, instabilities, kinetic plasma processes
National Category
Astronomy, Astrophysics and Cosmology Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-399975 (URN)10.3389/fspas.2019.00070 (DOI)000499869100001 ()
Funder
Swedish National Space Board, 128/17Swedish Research Council, 2016-05507
Available from: 2019-12-17 Created: 2019-12-17 Last updated: 2019-12-17Bibliographically approved
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
Burch, J. L., Dokgo, K., Hwang, K. J., Torbert, R. B., Graham, D. B., Webster, J. M., . . . Le Contel, O. (2019). High-Frequency Wave Generation in Magnetotail Reconnection: Linear Dispersion Analysis. Geophysical Research Letters, 46(8), 4089-4097
Open this publication in new window or tab >>High-Frequency Wave Generation in Magnetotail Reconnection: Linear Dispersion Analysis
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2019 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 8, p. 4089-4097Article in journal (Refereed) Published
Abstract [en]

Plasma and wave measurements from the NASA Magnetospheric Multiscale mission are presented for magnetotail reconnection events on 3 July and 11 July 2017. Linear dispersion analyses were performed using distribution functions comprising up to six drifting bi-Maxwellian distributions. In both events electron crescent-shaped distributions are shown to be responsible for upper hybrid waves near the X-line. In an adjacent location within the 3 July event a monodirectional field-aligned electron beam drove parallel-propagating beam-mode waves. In the 11 July event an electron distribution consisting of a drifting core and two crescents was shown to generate upper-hybrid and beam-mode waves at three different frequencies, explaining the observed broadband waves. Multiple harmonics of the upper hybrid waves were observed but cannot be explained by the linear dispersion analysis since they result from nonlinear beam interactions. Plain Language Summary Magnetic reconnection is a process that occurs throughout the universe in ionized gases (plasmas) containing embedded magnetic fields. This process converts magnetic energy to electron and ion energy, causing phenomena such as solar flares and auroras. The NASA Magnetospheric Multiscale mission has shown that in magnetic reconnection regions there are intense electric field oscillations or waves and that electrons form crescent and beam-like populations propagating both along and perpendicular to the magnetic field. This study shows that the observed electron populations are responsible for high-frequency waves including their propagation directions and frequency ranges.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2019
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-387210 (URN)10.1029/2019GL082471 (DOI)000467949200003 ()
Available from: 2019-06-25 Created: 2019-06-25 Last updated: 2019-06-25Bibliographically approved
Dokgo, K., Hwang, K.-J., Burch, J. L., Choi, E., Yoon, P. H., Sibeck, D. G. & Graham, D. B. (2019). High-Frequency Wave Generation in Magnetotail Reconnection: Nonlinear Harmonics of Upper Hybrid Waves. Geophysical Research Letters, 46(14), 7873-7882
Open this publication in new window or tab >>High-Frequency Wave Generation in Magnetotail Reconnection: Nonlinear Harmonics of Upper Hybrid Waves
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2019 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 14, p. 7873-7882Article in journal (Refereed) Published
Abstract [en]

MMS3 spacecraft passed the vicinity of the electron diffusion region of magnetotail reconnection on 3 July 2017, observing discrepancies between perpendicular electron bulk velocities and (E) over right arrow x (B) over right arrow drift, and agyrotropic electron crescent distributions. Analyzing linear wave dispersions, Burch et al. (2019, https://doi.org/10.1029/2019GL082471) showed the electron crescent generates high-frequency waves. We investigate harmonics of upper-hybrid (UH) waves using both observation and particle-in-cell (PIC) simulation, and the generation of electromagnetic radiation from PIC simulation. Harmonics of UH are linearly polarized and propagate along the perpendicular direction to the ambient magnetic field. Compared with two-dimensional PIC simulation and nonlinear kinetic theory, we show that the nonlinear beam-plasma interaction between the agyrotropic electrons and the core electrons generates harmonics of UH. Moreover, PIC simulation shows that agyrotropic electron beam can lead to electromagnetic (EM) radiation at the plasma frequency and harmonics.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2019
Keywords
magnetic reconnection, nonlinear plasma waves, PIC simulation
National Category
Fusion, Plasma and Space Physics Geophysics
Identifiers
urn:nbn:se:uu:diva-393833 (URN)10.1029/2019GL083361 (DOI)000481818900002 ()
Available from: 2019-09-27 Created: 2019-09-27 Last updated: 2019-09-27Bibliographically approved
Zhao, J., Wang, T., Sin, C., Graham, D. B., Dunlop, M. W., He, J., . . . Wu, D. (2019). Ion and Electron Dynamics in the Presence of Mirror, Electromagnetic Ion Cyclotron, and Whistler Waves. Astrophysical Journal, 883(2), Article ID 185.
Open this publication in new window or tab >>Ion and Electron Dynamics in the Presence of Mirror, Electromagnetic Ion Cyclotron, and Whistler Waves
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2019 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 883, no 2, article id 185Article in journal (Refereed) Published
Abstract [en]

The wave particle cyclotron interaction is a basic process in collisionless plasmas, which results in the redistribution of the energy between plasma waves and charged particles. This paper presents an event observation in order to explore the dynamics of charged particles and plasma waves, i.e., mirror, electromagnetic ion cyclotron (EMIC), and whistler waves, in the Earth's magnetosheath. It shows that when ions have a high-speed streaming velocity parallel to the magnetic field, EMIC waves arise. We also find that the frequency distribution of nearly parallel and nearly antiparallel whistler waves depends on the parallel streaming velocity of electrons. Based on the linear kinetic theory and the fitting plasma parameters, we show that the differential flows among ion components can enhance the ion cyclotron anisotropy instability that is even stronger than the mirror instability. The differential electron flows induce an asymmetry of the growth rate of counter-propagating whistler waves in the electron cyclotron anisotropy instability. On the other hand, the low-frequency EMIC and transverse electromagnetic waves modulate the ion pitch angle distribution. Moreover, when charged particles flow across the magnetic field, both low- and high-energy electrons are deeply trapped by mirror waves. These results illustrate new features of the observed plasma waves and charged particles in the Earth's magnetosheath, which could inspire improvement of the wave models therein.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2019
Keywords
instabilities, plasmas, waves
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-398688 (URN)10.3847/1538-4357/ab3db1 (DOI)000498390600044 ()
Funder
Swedish National Space Board, 128/17EU, Horizon 2020, 664931
Available from: 2019-12-09 Created: 2019-12-09 Last updated: 2019-12-09Bibliographically approved
Fuselier, S. A., Trattner, K. J., Petrinec, S. M., Denton, M. H., Toledo-Redondo, S., André, M., . . . Strangeway, R. J. (2019). Mass Loading the Earth's Dayside Magnetopause Boundary Layer and Its Effect on Magnetic Reconnection. Geophysical Research Letters, 46(12), 6204-6213
Open this publication in new window or tab >>Mass Loading the Earth's Dayside Magnetopause Boundary Layer and Its Effect on Magnetic Reconnection
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2019 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 12, p. 6204-6213Article in journal (Refereed) Published
Abstract [en]

When the interplanetary magnetic field is northward for a period of time, O+ from the high-latitude ionosphere escapes along reconnected magnetic field lines into the dayside magnetopause boundary layer. Dual-lobe reconnection closes these field lines, which traps O+ and mass loads the boundary layer. This O+ is an additional source of magnetospheric plasma that interacts with magnetosheath plasma through magnetic reconnection. This mass loading and interaction is illustrated through analysis of a magnetopause crossing by the Magnetospheric Multiscale spacecraft. While in the O+-rich boundary layer, the interplanetary magnetic field turns southward. As the Magnetospheric Multiscale spacecraft cross the high-shear magnetopause, reconnection signatures are observed. While the reconnection rate is likely reduced by the mass loading, reconnection is not suppressed at the magnetopause. The high-latitude dayside ionosphere is therefore a source of magnetospheric ions that contributes often to transient reduction in the reconnection rate at the dayside magnetopause.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2019
Keywords
magnetic reconnection, magnetosphere-ionosphere coupling, magnetopause, boundary layers
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-392876 (URN)10.1029/2019GL082384 (DOI)000477616300006 ()
Available from: 2019-09-26 Created: 2019-09-26 Last updated: 2019-12-12Bibliographically approved
Voros, Z., Yordanova, E., Graham, D. B., Khotyaintsev, Y. V. & Narita, Y. (2019). MMS Observations of Whistler and Lower Hybrid Drift Waves Associated with Magnetic Reconnection in the Turbulent Magnetosheath. Journal of Geophysical Research - Space Physics
Open this publication in new window or tab >>MMS Observations of Whistler and Lower Hybrid Drift Waves Associated with Magnetic Reconnection in the Turbulent Magnetosheath
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2019 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402Article in journal (Refereed) Published
Abstract [en]

Magnetic reconnection (MR) and the associated concurrently occurring waves have been extensively studied at large-scale plasma boundaries, in quasi-symmetric and asymmetric configurations in the terrestrial magnetotail and at the magnetopause. Recent high-resolution observations by MMS (Magnetospheric Multiscale) spacecraft indicate that MR can occur also in the magnetosheath where the conditions are highly turbulent when the upstream shock geometry is quasi-parallel. The strong turbulent motions make the boundary conditions for evolving MR complicated. In this paper it is demonstrated that the wave observations in localized regions of MR can serve as an additional diagnostic tool reinforcing our capacity for identifying MR events in turbulent plasmas. It is shown that in a close resemblance with MR at large-scale boundaries, turbulent reconnection associated whistler waves occur at separatrix/outflow regions and at the outer boundary of the electron diffusion region, while lower hybrid drift waves are associated with density gradients during the crossing of the current sheet. The lower hybrid drift instability can make the density inhomogeneities rippled. The identification of MR associated waves in the magnetosheath represents also an important milestone for developing a better understanding of energy redistribution and dissipation in turbulent plasmas.

National Category
Astronomy, Astrophysics and Cosmology Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-397642 (URN)10.1029/2019JA027028 (DOI)000494921200001 ()
Funder
Swedish Civil Contingencies Agency, 2016-2102
Note

Early View: Online Version of Record before inclusion in an issue

Available from: 2019-11-22 Created: 2019-11-22 Last updated: 2019-11-22Bibliographically 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
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
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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ORCID iD: ORCID iD iconorcid.org/0000-0002-1046-746x

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