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Li, W. Y., Graham, D. B., Khotyaintsev, Y. V., Vaivads, A., André, M., Min, K., . . . Burch, J. L. (2020). Electron Bernstein waves driven by electron crescents near the electron diffusion region. Nature Communications, 11(1), Article ID 141.
Open this publication in new window or tab >>Electron Bernstein waves driven by electron crescents near the electron diffusion region
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2020 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 11, no 1, article id 141Article in journal (Refereed) Published
Abstract [en]

The Magnetospheric Multiscale (MMS) spacecraft encounter an electron diffusion region (EDR) of asymmetric magnetic reconnection at Earth’s magnetopause. The EDR is characterized by agyrotropic electron velocity distributions on both sides of the neutral line. Various types of plasma waves are produced by the magnetic reconnection in and near the EDR. Here we report large-amplitude electron Bernstein waves (EBWs) at the electron-scale boundary of the Hall current reversal. The finite gyroradius effect of the outflow electrons generates the crescent-shaped agyrotropic electron distributions, which drive the EBWs. The EBWs propagate toward the central EDR. The amplitude of the EBWs is sufficiently large to thermalize and diffuse electrons around the EDR. The EBWs contribute to the cross-field diffusion of the electron-scale boundary of the Hall current reversal near the EDR.

Place, publisher, year, edition, pages
Nature Research, 2020
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-267776 (URN)10.1038/s41467-019-13920-w (DOI)000511897900002 ()31919351 (PubMedID)2-s2.0-85077697342 (Scopus ID)
Note

QC 20200304

Available from: 2020-03-04 Created: 2020-03-04 Last updated: 2020-03-04Bibliographically approved
Li, W. Y., Graham, D. B., Khotyaintsev, Y. V. V., Vaivads, A., Andre, M., Min, K., . . . Burch, J. L. (2020). Electron Bernstein waves driven by electron crescents near the electron diffusion region. Nature Communications, 11(1), Article ID 141.
Open this publication in new window or tab >>Electron Bernstein waves driven by electron crescents near the electron diffusion region
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2020 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 11, no 1, article id 141Article in journal (Refereed) Published
Abstract [en]

The Magnetospheric Multiscale (MMS) spacecraft encounter an electron diffusion region (EDR) of asymmetric magnetic reconnection at Earth's magnetopause. The EDR is characterized by agyrotropic electron velocity distributions on both sides of the neutral line. Various types of plasma waves are produced by the magnetic reconnection in and near the EDR. Here we report large-amplitude electron Bernstein waves (EBWs) at the electron-scale boundary of the Hall current reversal. The finite gyroradius effect of the outflow electrons generates the crescent-shaped agyrotropic electron distributions, which drive the EBWs. The EBWs propagate toward the central EDR. The amplitude of the EBWs is sufficiently large to thermalize and diffuse electrons around the EDR. The EBWs contribute to the cross-field diffusion of the electron-scale boundary of the Hall current reversal near the EDR.

Place, publisher, year, edition, pages
NATURE PUBLISHING GROUP, 2020
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-269041 (URN)10.1038/s41467-019-13920-w (DOI)000511897900002 ()31919351 (PubMedID)2-s2.0-85077697342 (Scopus ID)
Note

QC 20200311

Available from: 2020-03-11 Created: 2020-03-11 Last updated: 2020-03-11
Amano, T., Katou, T., Kitamura, N., Oka, M., Matsumoto, Y., Hoshino, M., . . . Blake, J. B. (2020). Observational Evidence for Stochastic Shock Drift Acceleration of Electrons at the Earth's Bow Shock. Physical Review Letters, 124(6), Article ID 065101.
Open this publication in new window or tab >>Observational Evidence for Stochastic Shock Drift Acceleration of Electrons at the Earth's Bow Shock
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2020 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 124, no 6, article id 065101Article in journal (Refereed) Published
Abstract [en]

The first-order Fermi acceleration of electrons requires an injection of electrons into a mildly relativistic energy range. However, the mechanism of injection has remained a puzzle both in theory and observation. We present direct evidence for a novel stochastic shock drift acceleration theory for the injection obtained with Magnetospheric Multiscale observations at the Earth's bow shock. The theoretical model can explain electron acceleration to mildly relativistic energies at high-speed astrophysical shocks, which may provide a solution to the long-standing issue of electron injection.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2020
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-270914 (URN)10.1103/PhysRevLett.124.065101 (DOI)000513568400010 ()32109113 (PubMedID)2-s2.0-85080915359 (Scopus ID)
Note

QC 20200324

Available from: 2020-03-24 Created: 2020-03-24 Last updated: 2020-03-24Bibliographically approved
Tang, B.-B. -., Li, W. Y., 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. 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
AMER GEOPHYSICAL UNION, 2019
Keywords
agyrotropic electron distributions, electron finite gyroradius effect, upper hybrid waves
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-251342 (URN)10.1029/2019GL082231 (DOI)000464650400002 ()2-s2.0-85063125578 (Scopus ID)
Note

QC 20190521

Available from: 2019-05-21 Created: 2019-05-21 Last updated: 2019-05-21Bibliographically approved
Chen, L.-J. -., Wang, S., Hesse, M., Ergun, R. E., Moore, T., Giles, B., . . . Lindqvist, P.-A. (2019). Electron Diffusion Regions in Magnetotail Reconnection Under Varying Guide Fields. Geophysical Research Letters, 46(12), 6230-6238
Open this publication in new window or tab >>Electron Diffusion Regions in Magnetotail Reconnection Under Varying Guide Fields
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2019 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 12, p. 6230-6238Article in journal (Refereed) Published
Abstract [en]

Kinetic structures of electron diffusion regions (EDRs) under finite guide fields in magnetotail reconnection are reported. The EDRs with guide fields 0.14–0.5 (in unit of the reconnecting component) are detected by the Magnetospheric Multiscale spacecraft. The key new features include the following: (1) cold inflowing electrons accelerated along the guide field and demagnetized at the magnetic field minimum while remaining a coherent population with a low perpendicular temperature, (2) wave fluctuations generating strong perpendicular electron flows followed by alternating parallel flows inside the reconnecting current sheet under an intermediate guide field, and (3) gyrophase bunched electrons with high parallel speeds leaving the X-line region. The normalized reconnection rates for the three EDRs range from 0.05 to 0.3. The measurements reveal that finite guide fields introduce new mechanisms to break the electron frozen-in condition.

Place, publisher, year, edition, pages
Blackwell Publishing, 2019
National Category
Geosciences, Multidisciplinary
Identifiers
urn:nbn:se:kth:diva-262616 (URN)10.1029/2019GL082393 (DOI)000477616300009 ()2-s2.0-85068146069 (Scopus ID)
Note

QC 20191024

Available from: 2019-10-24 Created: 2019-10-24 Last updated: 2019-10-24Bibliographically approved
Phan, T. D., Eastwood, J. P., Shay, M. A., Drake, J. F., Sonnerup, B. U., Fujimoto, M., . . . Magnes, W. (2019). Electron magnetic reconnection without ion coupling in Earth's turbulent magnetosheath (vol 557, pg 202, 2018). Nature, 569(7757), E9-E9
Open this publication in new window or tab >>Electron magnetic reconnection without ion coupling in Earth's turbulent magnetosheath (vol 557, pg 202, 2018)
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2019 (English)In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 569, no 7757, p. E9-E9Article in journal (Refereed) Published
Place, publisher, year, edition, pages
NATURE PUBLISHING GROUP, 2019
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-264749 (URN)10.1038/s41586-019-1208-1 (DOI)000468844100010 ()31073227 (PubMedID)2-s2.0-85065580542 (Scopus ID)
Note

QC 20191202

Available from: 2019-12-02 Created: 2019-12-02 Last updated: 2020-03-09Bibliographically approved
Oka, M., Otsuka, F., Matsukiyo, S., Wilson, L. B., Argall, M. R., Amano, T., . . . Lindqvist, P.-A. (2019). Electron Scattering by Low-frequency Whistler Waves at Earth?s Bow Shock. Astrophysical Journal, 886(1), Article ID 53.
Open this publication in new window or tab >>Electron Scattering by Low-frequency Whistler Waves at Earth?s Bow Shock
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2019 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 886, no 1, article id 53Article in journal (Refereed) Published
Abstract [en]

Electrons are accelerated to nonthermal energies at shocks in space and astrophysical environments. While shock drift acceleration (SDA) has been considered a key process of electron acceleration at Earth?s bow shock, it has also been recognized that SDA needs to be combined with an additional stochastic process to explain the observed power-law energy spectra. Here, we show mildly energetic (?0.5 keV) electrons are locally scattered (and accelerated while being confined) by magnetosonic-whistler waves within the shock transition layer, especially when the shock angle is large (<CDATA<i). When measured by the Magnetospheric Multiscale mission at a high cadence, ?0.5 keV electron flux increased exponentially in the shock transition layer. However, the flux profile was not entirely smooth and the fluctuation showed temporal/spectral association with large-amplitude (<CDATA<i), low-frequency (<CDATA<i where <CDATA<i is the cyclotron frequency), obliquely propagating (<CDATA<i, where <CDATA<i is the angle between the wave vector and background magnetic field) whistler waves, indicating that the particles were interacting with the waves. Particle simulations demonstrate that, although linear cyclotron resonances with ?0.5 keV electrons are unlikely due to the obliquity and low frequencies of the waves, the electrons are still scattered beyond 90; pitch angle by (1) resonant mirroring (transit-time damping), (2) non-resonant mirroring, and (3) subharmonic cyclotron resonances. Such coupled nonlinear scattering processes are likely to provide the stochasticity needed to explain the power-law formation.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2019
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-265500 (URN)10.3847/1538-4357/ab4a81 (DOI)000499366900001 ()2-s2.0-85077337545 (Scopus ID)
Note

QC 20191217

Available from: 2019-12-17 Created: 2019-12-17 Last updated: 2020-03-09Bibliographically approved
Zhou, M., Huang, J., Man, H. Y., Deng, X. H., Zhong, Z. H., Russell, C. T., . . . Burch, J. L. (2019). Electron-scale Vertical Current Sheets in a Bursty Bulk Flow in the Terrestrial Magnetotail. Astrophysical Journal Letters, 872(2), Article ID L26.
Open this publication in new window or tab >>Electron-scale Vertical Current Sheets in a Bursty Bulk Flow in the Terrestrial Magnetotail
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2019 (English)In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 872, no 2, article id L26Article in journal (Refereed) Published
Abstract [en]

We report Magnetospheric Multiscale observations of multiple vertical current sheets (CSs) in a bursty bulk flow in the near-Earth magnetotail. Two of the CSs were fine structures of a dipolarization front (DF) at the leading edge of the flow. The other CSs were a few Earth radii tailward of the DF; that is, in the wake of the DF. Some of these vertical CSs were a few electron inertial lengths thick and were converting energy from magnetic field to plasma. The currents of the CSs in the DF wake were carried by electrons that formed flow shear layers. These electron-scale CSs were probably formed during the turbulent evolution of the bursty bulk flow and are important for energy conversion associated with fast flows.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2019
Keywords
magnetic fields, magnetic reconnection, turbulence
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-245912 (URN)10.3847/2041-8213/ab0424 (DOI)000459254000007 ()2-s2.0-85063470589 (Scopus ID)
Note

QC 220190314

Available from: 2019-03-14 Created: 2019-03-14 Last updated: 2019-05-16Bibliographically approved
Vines, S. K., Allen, R. C., Anderson, B. J., Engebretson, M. J., Fuselier, S. A., Russell, C. T., . . . Burch, J. L. (2019). EMIC Waves in the Outer Magnetosphere: Observations of an Off-Equator Source Region. Geophysical Research Letters, 46(11), 5707-5716
Open this publication in new window or tab >>EMIC Waves in the Outer Magnetosphere: Observations of an Off-Equator Source Region
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2019 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 11, p. 5707-5716Article in journal (Refereed) Published
Abstract [en]

Electromagnetic ion cyclotron (EMIC) waves at large L shells were observed away from the magnetic equator by the Magnetospheric MultiScale (MMS) mission nearly continuously for over four hours on 28 October 2015. During this event, the wave Poynting vector direction systematically changed from parallel to the magnetic field (toward the equator), to bidirectional, to antiparallel (away from the equator). These changes coincide with the shift in the location of the minimum in the magnetic field in the southern hemisphere from poleward to equatorward of MMS. The local plasma conditions measured with the EMIC waves also suggest that the outer magnetospheric region sampled during this event was generally unstable to EMIC wave growth. Together, these observations indicate that the bidirectionally propagating wave packets were not a result of reflection at high latitudes but that MMS passed through an off-equator EMIC wave source region associated with the local minimum in the magnetic field.

Place, publisher, year, edition, pages
Blackwell Publishing, 2019
National Category
Geophysics
Identifiers
urn:nbn:se:kth:diva-262624 (URN)10.1029/2019GL082152 (DOI)000477616200009 ()31423036 (PubMedID)2-s2.0-85067631852 (Scopus ID)
Note

QC 20191018

Available from: 2019-10-18 Created: 2019-10-18 Last updated: 2019-10-18Bibliographically approved
Torkar, K., Nakamura, R., Wellenzohn, S., Jeszenszky, H., Torbert, R. B., Lindqvist, P.-A., . . . Giles, B. L. (2019). Improved Determination of Plasma Density Based on Spacecraft Potential of the Magnetospheric Multiscale Mission Under Active Potential Control. IEEE Transactions on Plasma Science, 47(8), 3636-3647
Open this publication in new window or tab >>Improved Determination of Plasma Density Based on Spacecraft Potential of the Magnetospheric Multiscale Mission Under Active Potential Control
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2019 (English)In: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 47, no 8, p. 3636-3647Article in journal (Refereed) Published
Abstract [en]

Data from the Magnetospheric Multiscale (MMS) mission, in particular, the spacecraft potential measured with and without the ion beams of the active spacecraft potential control (ASPOC) instruments, plasma electron moments, and the electric field, have been employed for an improved determination of plasma density based on spacecraft potential. The known technique to derive plasma density from spacecraft potential sees the spacecraft behaving as a plasma probe which adopts a potential at which the ambient plasma current and one of photoelectrons produced at the surface and leaving into space are in equilibrium. Thus, the potential is a function of the plasma current, and plasma density can be determined using measurements or assumptions on plasma temperature. This method is especially useful during periods when the plasma instruments are not in operation or when spacecraft potential data have significantly higher time resolution than particle detectors. However, the applicable current-voltage characteristic of the spacecraft has to be known with high accuracy, particularly when the potential is actively controlled and shows only minor residual variations. This paper demonstrates recent refinements of the density determination coming from: 1) the reduction of artifacts in the potential data due to the geometry of the spinning spacecraft and due to effects of the ambient electric field on the potential measurements and 2) a calibration of the plasma current to the spacecraft surfaces which is only possible by comparison with the variable currents from the ion beams of ASPOC. The results are discussed, and plasma densities determined by this method are shown in comparison with measurements by the Fast Plasma Instrument (FPI) for some intervals of the MMS mission.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2019
Keywords
Electrostatic potentials, ion emission, magnetosphere, plasma measurements, space vehicles, surface charging
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-257647 (URN)10.1109/TPS.2019.2911425 (DOI)000480316700003 ()2-s2.0-85070453252 (Scopus ID)
Note

QC 20190904

Available from: 2019-09-04 Created: 2019-09-04 Last updated: 2019-09-04Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0001-5617-9765

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