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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 ()
Note

QC 220190314

Available from: 2019-03-14 Created: 2019-03-14 Last updated: 2019-03-14Bibliographically 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
AMER GEOPHYSICAL UNION, 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: 2019-02-19Bibliographically 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
Yao, S. T., Shi, Q. Q., Yao, Z. H., Li, J. X., Yue, C., Tao, X., . . . Giles, B. L. (2019). Waves in Kinetic-Scale Magnetic Dips: MMS Observations in the Magnetosheath. Geophysical Research Letters, 46(2), 523-533
Open this publication in new window or tab >>Waves in Kinetic-Scale Magnetic Dips: MMS Observations in the Magnetosheath
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2019 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 2, p. 523-533Article in journal (Refereed) Published
Abstract [en]

Kinetic scale magnetic dips (KSMDs), with a significant depression in magnetic field strength, and scale length close to and less than one proton gyroradius, were reported in the turbulent plasmas both in recent observation and numerical simulation studies. These KSMDs likely play important roles in energy conversion and dissipation. In this study, we present observations of the KSMDs that are labeled whistler mode waves, electrostatic solitary waves, and electron cyclotron waves in the magnetosheath. The observations suggest that electron temperature anisotropy or beams within KSMD structures provide free energy to generate these waves. In addition, the occurrence rates of the waves are higher in the center of the magnetic dips than at their edges, implying that the KSMDs might be the origin of various kinds of waves. We suggest that the KSMDs could provide favorable conditions for the generation of waves and transfer energy to the waves in turbulent magnetosheath plasmas. Plain Language Summary The Earth's magnetosheath is a turbulent plasma environment where energy conversion, particle acceleration, and mass and momentum transport take place. Many of these key processes involve kinetic-scale physics. However, in-depth studies from previous missions are limited by their lower spacecraft data resolution. The recent Magnetospheric Multiscale (MMS) mission provides us with a large amount of high-temporal cadence data for studying kinetic-scale physics in the magnetosheath. In this study, we report whistler mode waves, electrostatic solitary waves and electron cyclotron waves within kinetic-scale magnetic dips (KSMDs) that can be generated in the turbulent magnetosheath. These waves could be excited by electron temperature anisotropy or beams. As is well known, plasma waves are important processes in converting energy, accelerating and scattering electrons and ions, and modifying the distributions of charged particles. If plasma instabilities develop within the KSMDs, the resulting waves could absorb free energy from plasma particles and may propagate out of the KSMDs. Thus, our discoveries could significantly advance the understanding of energy conversion and dissipation for kinetic-scale turbulence. This study provides a new reference not only for observations in space physics but also for related basic plasma theories and numerical simulations.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2019
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-245166 (URN)10.1029/2018GL080696 (DOI)000458607400001 ()2-s2.0-85060180006 (Scopus ID)
Note

QC 20190307

Available from: 2019-03-07 Created: 2019-03-07 Last updated: 2019-03-07Bibliographically approved
Wang, R., Lu, Q., Nakamura, R., Baumjohann, W., Huang, C., Russell, C. T., . . . Giles, B. (2018). An Electron-Scale Current Sheet Without Bursty Reconnection Signatures Observed in the Near-Earth Tail. Geophysical Research Letters, 45(10), 4542-4549
Open this publication in new window or tab >>An Electron-Scale Current Sheet Without Bursty Reconnection Signatures Observed in the Near-Earth Tail
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2018 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 10, p. 4542-4549Article in journal (Refereed) Published
Abstract [en]

Observations of a current sheet as thin as the electron scale are extremely rare in the near-Earth magnetotail. By measurement from the novel Magnetospheric Multiscale mission in the near-Earth magnetotail, we identified such an electron-scale current sheet and determined its detailed properties. The electron current sheet was bifurcated, with a half-thickness of nine electron inertial lengths, and was sandwiched between the Hall field. Because of the strong Hall electric field, the super-Alfvenic electron bulk flows were created mainly by the electric field drift, leading to the generation of the strong electron current. Inevitably, a bifurcated current sheet was formed since the Hall electric field was close to zero at the center of the current sheet. Inside the electron current sheet, the electrons were significantly heated while the ion temperature showed no change. The ions kept moving at a low speed, which was not affected by this electron current sheet. The energy dissipation was negligible inside the current sheet. The observations indicate that a thin current sheet, even as thin as electron scale, is not the sufficient condition for triggering bursty reconnection.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2018
Keywords
magnetotail, current sheet, magnetic reconnection
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-231737 (URN)10.1002/2017GL076330 (DOI)000435262000002 ()2-s2.0-85047539723 (Scopus ID)
Note

QC 20180703

Available from: 2018-07-03 Created: 2018-07-03 Last updated: 2018-07-03Bibliographically approved
Hamrin, M., Gunell, H., Lindkvist, J., Lindqvist, P.-A., Ergun, R. E. & Giles, B. L. (2018). Bow Shock Generator Current Systems: MMS Observations of Possible Current Closure. Journal of Geophysical Research - Space Physics, 123(1), 242-258
Open this publication in new window or tab >>Bow Shock Generator Current Systems: MMS Observations of Possible Current Closure
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2018 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 1, p. 242-258Article in journal (Refereed) Published
Abstract [en]

We use data from the first two dayside seasons of the Magnetospheric Multiscale (MMS) mission to study current systems associated with quasi-perpendicular bow shocks of generator type. We have analyzed 154 MMS bow shock crossings near the equatorial plane. We compute the current density during the crossings and conclude that the component perpendicular to the shock normal (J) is consistent with a pileup of the interplanetary magnetic field (IMF) inside the magnetosheath. For predominantly southward IMF, we observe a component J(n) parallel (antiparallel) to the normal for GSM gamma > 0 (<0), and oppositely directed for northward IMF. This indicates current closure across the equatorial magnetosheath, and it is observed for IMF clock angles near 0 degrees and 180 degrees. To our knowledge, these are the first observational evidence for bow shock current closure across the magnetosheath. Since we observe no clear signatures of vertical bar J(perpendicular to)vertical bar decreasing toward large vertical bar Y vertical bar we suggest that the main region of current closure is further tailward, outside MMS probing region. For IMF clock angles near 90 degrees, we find indications of the current system being tilted toward the north-south direction, obtaining a significant J(z) component, and we suggest that the current closes off the equatorial plane at higher latitudes where the spacecraft are not probing. The observations are complicated for several reasons. For example, variations in the solar wind and the magnetospheric currents and loads affect the closure, and J(n) is distributed over large regions, making it difficult to resolve inside the magnetosheath proper.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2018
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-224068 (URN)10.1002/2017JA024826 (DOI)000425637600018 ()2-s2.0-85040246253 (Scopus ID)
Note

QC 20180314

Available from: 2018-03-14 Created: 2018-03-14 Last updated: 2018-03-14Bibliographically approved
Vaverka, J., Nakamura, T., Kero, J., Mann, I., De Spiegeleer, A., Hamrin, M., . . . Pellinen-Wannberg, A. (2018). Comparison of Dust Impact and Solitary Wave Signatures Detected by Multiple Electric Field Antennas Onboard the MMS Spacecraft. Journal of Geophysical Research - Space Physics, 123(8), 6119-6129
Open this publication in new window or tab >>Comparison of Dust Impact and Solitary Wave Signatures Detected by Multiple Electric Field Antennas Onboard the MMS Spacecraft
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2018 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 8, p. 6119-6129Article in journal (Refereed) Published
Abstract [en]

Dust impact detection by electric field instruments is a relatively new method. However, the influence of dust impacts on electric field measurements is not completely understood and explained. A better understanding is very important for reliable dust impact identification, especially in environments with low dust impact rate. Using data from Earth-orbiting Magnetospheric Multiscale mission (MMS) spacecraft, we present a study of various pulses detected simultaneously by multiple electric field antennas in the monopole (probe-to-spacecraft potential measurement) and dipole (probe-to-probe potential measurement) configurations. The study includes data obtained during an impact of a millimeter-sized object. We show that the identification of dust impacts by a single antenna is a very challenging issue in environments where solitary waves are commonly present and that some pulses can be easily misinterpreted as dust impacts. We used data from multiple antennas to distinguish between changes in the spacecraft potential (dust impact) and structures in the ambient plasma or electric field. Our results indicate that an impact cloud is in some cases able to influence the potential of the electric field antenna during its expansion.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2018
Keywords
dust, solitary waves, electric field instruments, MMS, dust impacts
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-236024 (URN)10.1029/2018JA025380 (DOI)000445731300002 ()2-s2.0-85052462999 (Scopus ID)
Note

QC 20181012

Available from: 2018-10-12 Created: 2018-10-12 Last updated: 2018-10-30Bibliographically approved
Denton, R. E., Sonnerup, B. U., Russell, C. T., Hasegawa, H., Phan, T.-D. -., Strangeway, R. J., . . . Vines, S. K. (2018). Determining L-M-N Current Sheet Coordinates at the Magnetopause From Magnetospheric Multiscale Data. Journal of Geophysical Research - Space Physics, 123(3), 2274-2295
Open this publication in new window or tab >>Determining L-M-N Current Sheet Coordinates at the Magnetopause From Magnetospheric Multiscale Data
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2018 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 3, p. 2274-2295Article in journal (Refereed) Published
Abstract [en]

We discuss methods to determine L-M-N coordinate systems for current sheet crossings observed by the Magnetospheric Multiscale (MMS) spacecraft mission during ongoing reconnection, where e(L) is the direction of the reconnecting component of the magnetic field, B, and e(N) is normal to the magnetopause. We present and test a new hybrid method, with e(L) estimated as the maximum variance direction of B (MVAB) and e(N) as the direction of maximum directional derivative of B, and then adjust these directions to be perpendicular. In the best case, only small adjustment is needed. Results from this method, applied to an MMS crossing of the dayside magnetopause at 1305:45UT on 16 October 2015, are discussed and compared with those from other methods for which e(N) is obtained by other means. Each of the other evaluations can be combined with e(L) from MVAB in a generalized hybrid approach to provide an L-M-N system. The quality of the results is judged by eigenvalue ratios, constancy of directions using different data segments and methods, and expected sign and magnitude of the normal component of B. For this event, the hybrid method appears to produce e(N) accurate to within less than 10 degrees. We discuss variance analysis using the electric current density, J, or the J x B force, which yield promising results, and minimum Faraday residue analysis and MVAB alone, which can be useful for other events. We also briefly discuss results from our hybrid method and MVAB alone for a few other MMS reconnection events. Plain Language Summary We discuss methods for determining coordinate systems in order to study magnetic reconnection events at the magnetopause, the boundary between the ionized gas in the region of space dominated by the Earth's magnetic field and the ionized gas coming from the solar wind. We introduce a new method that combines results from multiple methods in order to determine the three coordinate directions in space. We demonstrate this method by applying it to an event observed by the Magnetospheric Multiscale spacecraft on 16 October 2015 and at other times.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2018
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-227238 (URN)10.1002/2017JA024619 (DOI)000430125300041 ()2-s2.0-85044210088 (Scopus ID)
Note

QC 20180518

Available from: 2018-05-18 Created: 2018-05-18 Last updated: 2018-05-18Bibliographically approved
Alm, L., Farrugia, C. J., Paulson, K. W., Argall, M. R., Torbert, R. B., Burch, J. L., . . . Giles, B. L. (2018). Differing Properties of Two Ion-Scale Magnetopause Flux Ropes. Journal of Geophysical Research - Space Physics, 123(1), 114-131
Open this publication in new window or tab >>Differing Properties of Two Ion-Scale Magnetopause Flux Ropes
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2018 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 1, p. 114-131Article in journal (Refereed) Published
Abstract [en]

In this paper, we present results from the Magnetospheric Multiscale constellation encountering two ion-scale, magnetopause flux ropes. The two flux ropes exhibit very different properties and internal structure. In the first flux rope, there are large differences in the currents observed by different satellites, indicating variations occurring over sub-d(i) spatial scales, and time scales on the order of the ion gyroperiod. In addition, there is intense wave activity and particle energization. The interface between the two flux ropes exhibits oblique whistler wave activity. In contrast, the second flux rope is mostly quiescent, exhibiting little activity throughout the encounter. Changes in the magnetic topology and field line connectivity suggest that we are observing flux rope coalescence.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2018
National Category
Geophysics
Identifiers
urn:nbn:se:kth:diva-224066 (URN)10.1002/2017JA024525 (DOI)000425637600010 ()2-s2.0-85042272503 (Scopus ID)
Note

QC 20180314

Available from: 2018-03-14 Created: 2018-03-14 Last updated: 2018-03-14Bibliographically approved
Oimatsu, S., Nose, M., Teramoto, M., Yamamoto, K., Matsuoka, A., Kasahara, S., . . . Lindqvist, P.-A. (2018). Drift-Bounce Resonance Between Pc5 Pulsations and Ions at Multiple Energies in the Nightside Magnetosphere: Arase and MMS Observations. Geophysical Research Letters, 45(15), 7277-7286
Open this publication in new window or tab >>Drift-Bounce Resonance Between Pc5 Pulsations and Ions at Multiple Energies in the Nightside Magnetosphere: Arase and MMS Observations
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2018 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 15, p. 7277-7286Article in journal (Refereed) Published
Abstract [en]

A Pc5 wave is observed by the Exploration of energization and Radiation in Geospace Arase satellite in the inner magnetosphere (L similar to 5.4-6.1) near postmidnight (L-magnetic local time similar to 1.8-2.5 hr) during the storm recovery phase on 27 March 2017. Its azimuthal wave number (m-number) is estimated using two independent methods with satellites and ground observations to be -8 to -15. The direct measurement of the m-number enables us to calculate the resonance energy. The flux oscillations of H+ and O+ ions at >= 56.3 keV are caused by drift resonance and those of O+ ions at <= 18.6 keV by bounce resonance. Resonances of O+ ions at multiple energies are simultaneously observed for the first time. The enhancement of the O+/H+ flux ratio at <= 18.6 keV indicates selective acceleration of O+ ions through bounce resonance. Plain Language Summary Geomagnetic pulsations are magnetic fluctuations excited by solar wind or plasma instabilities in the magnetosphere. Pc5 waves are continuous geomagnetic pulsations with a period of 150-600 s. A Pc5 wave was observed in the inner magnetosphere during a magnetic storm on 27 March 2017. It propagated westward with a wave number of 8 to 15 and resonated with charged particles, resulting in oscillations of the H+ and O+ ion fluxes at >= 56.3 keV and the O+ ion fluxes at <= 18.6 keV. Resonances of O+ ions at multiple energies are simultaneously observed for the first time. At the same time, the O+/H+ flux ratio at <= 18.6 keV enhanced corresponding to the O+ ion flux oscillations, which indicates selective acceleration of O+ ions through resonances.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2018
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-235133 (URN)10.1029/2018GL078961 (DOI)000443129500005 ()2-s2.0-85052570182 (Scopus ID)
Note

QC 20180919

Available from: 2018-09-19 Created: 2018-09-19 Last updated: 2018-09-19Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-5617-9765

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