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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
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
Goodrich, K. A., Ergun, R., Schwartz, S. J., Wilson, L. B., Johlander, A., Newman, D., . . . Giles, B. (2019). Impulsively Reflected Ions: A Plausible Mechanism for Ion Acoustic Wave Growth in Collisionless Shocks. Journal of Geophysical Research: Space Physics, 124(3), 1855-1865
Open this publication in new window or tab >>Impulsively Reflected Ions: A Plausible Mechanism for Ion Acoustic Wave Growth in Collisionless Shocks
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2019 (English)In: Journal of Geophysical Research: Space Physics, Vol. 124, no 3, p. 1855-1865Article in journal (Refereed) Published
Abstract [en]

We present recent high time resolution observations from an oblique (43 degrees) shock crossing from the Magnetospheric Multiscale mission. Short-duration bursts between 10 and 100 ms of ion acoustic waves are observed in this event alongside a persistent reflected ion population. High time resolution (150 ms) particle measurements show strongly varying ion distributions between successive measurements, implying that they are bursty and impulsive by nature. Such signatures are consistent with ion bursts that are impulsively reflected at various points within the shock. We find that, after instability analysis using a Fried-Conte dispersion solver, the insertion of dispersive ion bursts into an already stable ion distribution can lead to wave growth in the ion acoustic mode for short durations of time. We find that impulsively reflected ions are a plausible mechanism for ion acoustic wave growth in the terrestrial bow shock and, furthermore, suggest that wave growth can lead to a small but measurable momentum exchange between the solar wind ions and the reflected population.

Place, publisher, year, edition, pages
Blackwell Publishing Ltd, 2019
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-252042 (URN)10.1029/2018JA026436 (DOI)000466087900027 ()2-s2.0-85063577474 (Scopus ID)
Note

QC 20190731

Available from: 2019-07-31 Created: 2019-07-31 Last updated: 2019-07-31Bibliographically approved
Cozzani, G., Retino, A., Califano, F., Alexandrova, A., Contel, O. L., Khotyaintsev, Y., . . . 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
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-249783 (URN)10.1103/PhysRevE.99.043204 (DOI)000463898200002 ()2-s2.0-85064403029 (Scopus ID)
Note

QC 20190429

Available from: 2019-04-29 Created: 2019-04-29 Last updated: 2019-06-18Bibliographically approved
Li, B., Han, D.-S. -., Hu, Z.-J. -., Hu, H.-Q. -., Liu, J.-J. -., Dai, L., . . . Russell, C. T. (2019). Magnetospheric Multiscale Observations of ULF Waves and Correlated Low-Energy Ion Monoenergetic Acceleration. Journal of Geophysical Research - Space Physics
Open this publication in new window or tab >>Magnetospheric Multiscale Observations of ULF Waves and Correlated Low-Energy Ion Monoenergetic Acceleration
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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]

Low-energy ions of ionospheric origin with energies below 10s of electron volt dominate most of the volume and mass of the terrestrial magnetosphere. However, sunlit spacecraft often become positively charged to several 10s of volts, which prevents low-energy ions from reaching the particle detectors on the spacecraft. Magnetospheric Multiscale spacecraft (MMS) observations show that ultralow-frequency (ULF) waves drive low-energy ions to drift in the E × B direction with a drift velocity equal to V E × B , and low-energy ions were accelerated to sufficient total energy to be measured by the MMS/Fast Plasma Investigation Dual Ion Spectrometers. The maximum low-energy ion energy flux peak seen in MMS1's dual ion spectrometer measurements agreed well with the theoretical calculation of H + ion E × B drift energy. The density of ions in the energy range below minimum energy threshold was between 1 and 3 cm −3 in the magnetosphere subsolar region in this event.

Place, publisher, year, edition, pages
Blackwell Publishing Ltd, 2019
Keywords
E × B, low-energy ion, MMS, monoenergetic acceleration, ultralow-frequency wave
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-252232 (URN)10.1029/2018JA026372 (DOI)000477707800031 ()2-s2.0-85065024814 (Scopus ID)
Note

QC 20190614

Available from: 2019-06-14 Created: 2019-06-14 Last updated: 2019-08-20Bibliographically approved
Steinvall, K., Khotyaintsev, Y. V. 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 6km. 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(vertical bar), 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(vertical bar)approximate to 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 pancakes.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2019
Keywords
Electron holes
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-244119 (URN)10.1029/2018GL080757 (DOI)000456938600007 ()2-s2.0-85059915386 (Scopus ID)
Funder
Swedish National Space Board, 128/17Swedish Research Council, 2016-05507
Note

QC 20190219

Available from: 2019-02-19 Created: 2019-02-19 Last updated: 2019-06-18Bibliographically approved
Zhou, M., Deng, X. H., Zhong, Z. H., Pang, Y., Tang, R. X., El-Alaoui, M., . . . Lindqvist, P.-A. (2019). Observations of an Electron Diffusion Region in Symmetric Reconnection with Weak Guide Field. Astrophysical Journal, 870(1), Article ID 34.
Open this publication in new window or tab >>Observations of an Electron Diffusion Region in Symmetric Reconnection with Weak Guide Field
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2019 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 870, no 1, article id 34Article in journal (Refereed) Published
Abstract [en]

The Magnetospheric Multiscale spacecraft encountered an electron diffusion region (EDR) in a symmetric reconnection in the Earth's magnetotail. The EDR contained a guide field of about 2 nT, which was 13% of the magnetic field in the inflow region, and its thickness was about 2 local electron inertial lengths. Intense energy dissipation, a super-Alfvenic electron jet, electron nongyrotropy, and crescent-shaped electron velocity distributions were observed in association with this EDR. These features are similar to those of the EDRs in asymmetric reconnection at the dayside magnetopause. Electrons gained about 50% of their energy from the immediate upstream to the EDR. Crescent electron distributions were seen at the boundary of the EDR, while highly curved magnetic field lines inside the EDR may have gyrotropized the electrons. The EDR was characterized by a parallel current that was carried by antiparallel drifting electrons that were probably accelerated by a parallel electric field along the guide field. These results reveal the essential electron physics of the EDR and provide a significant example of an EDR in symmetric reconnection with a weak guide field.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
magnetic reconnection, Sun: heliosphere
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-241319 (URN)10.3847/1538-4357/aaf16f (DOI)000455043900001 ()2-s2.0-85059838467 (Scopus ID)
Note

QC 20190125

Available from: 2019-01-25 Created: 2019-01-25 Last updated: 2019-01-25Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0001-5617-9765

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