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Liu, C. M., Fu, H. S., Vaivads, A., Khotyaintsev, Y. V., Gershman, D. J., Hwang, K.-J., . . . Le Contel, O. (2018). Electron Jet Detected by MMS at Dipolarization Front. Geophysical Research Letters, 45(2), 556-564
Open this publication in new window or tab >>Electron Jet Detected by MMS at Dipolarization Front
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2018 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 2, p. 556-564Article in journal (Refereed) Published
Abstract [en]

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

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2018
Keywords
electron jet, dipolarization front, electric field, LHD waves, electron current, energy conversion
National Category
Fusion, Plasma and Space Physics Geophysics
Identifiers
urn:nbn:se:uu:diva-347650 (URN)10.1002/2017GL076509 (DOI)000425514300009 ()
Available from: 2018-04-06 Created: 2018-04-06 Last updated: 2018-04-06Bibliographically approved
Graham, D. B., Vaivads, A., Khotyaintsev, Y. V., André, M., Le Contel, O., Malaspina, D. M., . . . Torbert, R. B. (2018). Large-Amplitude High-Frequency Waves at Earth's Magnetopause. Journal of Geophysical Research - Space Physics, 123(4), 2630-2657
Open this publication in new window or tab >>Large-Amplitude High-Frequency Waves at Earth's Magnetopause
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2018 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 4, p. 2630-2657Article in journal (Refereed) Published
Abstract [en]

Large-amplitude waves near the electron plasma frequency are found by the Magnetospheric Multiscale (MMS) mission near Earth's magnetopause. The waves are identified as Langmuir and upper hybrid (UH) waves, with wave vectors either close to parallel or close to perpendicular to the background magnetic field. The waves are found all along the magnetopause equatorial plane, including both flanks and close to the subsolar point. The waves reach very large amplitudes, up to 1Vm(-1), and are thus among the most intense electric fields observed at Earth's magnetopause. In the magnetosphere and on the magnetospheric side of the magnetopause the waves are predominantly UH waves although Langmuir waves are also found. When the plasma is very weakly magnetized only Langmuir waves are likely to be found. Both Langmuir and UH waves are shown to have electromagnetic components, which are consistent with predictions from kinetic wave theory. These results show that the magnetopause and magnetosphere are often unstable to intense wave activity near the electron plasma frequency. These waves provide a possible source of radio emission at the magnetopause.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2018
Keywords
plasma waves, magnetopause
National Category
Fusion, Plasma and Space Physics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-357762 (URN)10.1002/2017JA025034 (DOI)000433498400012 ()
Funder
Swedish National Space Board, 175/15
Available from: 2018-08-23 Created: 2018-08-23 Last updated: 2018-08-23Bibliographically approved
Ergun, R. E., Goodrich, K. A., Wilder, F. D., Ahmadi, N., Holmes, J. C., Eriksson, S., . . . Vaivads, A. (2018). Magnetic Reconnection, Turbulence, and Particle Acceleration: Observations in the Earth's Magnetotail. Geophysical Research Letters, 45(8), 3338-3347
Open this publication in new window or tab >>Magnetic Reconnection, Turbulence, and Particle Acceleration: Observations in the Earth's Magnetotail
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2018 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 8, p. 3338-3347Article in journal (Refereed) Published
Abstract [en]

We report observations of turbulent dissipation and particle acceleration from large-amplitude electric fields (E) associated with strong magnetic field (B) fluctuations in the Earth's plasma sheet. The turbulence occurs in a region of depleted density with anti-earthward flows followed by earthward flows suggesting ongoing magnetic reconnection. In the turbulent region, ions and electrons have a significant increase in energy, occasionally > 100 keV, and strong variation. There are numerous occurrences of vertical bar E vertical bar > 100 mV/m including occurrences of large potentials (> 1 kV) parallel to B and occurrences with extraordinarily large J.E (J is current density). In this event, we find that the perpendicular contribution of J.E with frequencies near or below the ion cyclotron frequency (f(ci)) provide the majority net positive J.E. Large-amplitude parallel E events with frequencies above f(ci) to several times the lower hybrid frequency provide significant dissipation and can result in energetic electron acceleration. Plain Language Summary The Magnetospheric Multiscale mission is able to examine dissipation associated with magnetic reconnection with unprecedented accuracy and frequency response. The observations show that roughly 80% of the dissipation is from the perpendicular currents and electric fields. However, large-amplitude parallel electric fields appear to play a strong role in turbulent dissipation into electrons and in electron acceleration.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2018
National Category
Astronomy, Astrophysics and Cosmology Geophysics
Identifiers
urn:nbn:se:uu:diva-359672 (URN)10.1002/2018GL076993 (DOI)000435745500004 ()
Available from: 2018-09-05 Created: 2018-09-05 Last updated: 2018-09-05Bibliographically approved
Breuillard, H., Matteini, L., Argall, M. R., Sahraoui, F., Andriopoulou, M., Le Contel, O., . . . Cohen, I. J. (2018). New Insights into the Nature of Turbulence in the Earth's Magnetosheath Using Magnetospheric MultiScale Mission Data. Astrophysical Journal, 859(2), Article ID 127.
Open this publication in new window or tab >>New Insights into the Nature of Turbulence in the Earth's Magnetosheath Using Magnetospheric MultiScale Mission Data
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2018 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 859, no 2, article id 127Article in journal (Refereed) Published
Abstract [en]

The Earth's magnetosheath, which is characterized by highly turbulent fluctuations, is usually divided into two regions of different properties as a function of the angle between the interplanetary magnetic field and the shock normal. In this study, we make use of high-time resolution instruments on board the Magnetospheric MultiScale spacecraft to determine and compare the properties of subsolar magnetosheath turbulence in both regions, i. e., downstream of the quasi-parallel and quasi-perpendicular bow shocks. In particular, we take advantage of the unprecedented temporal resolution of the Fast Plasma Investigation instrument to show the density fluctuations down to sub-ion scales for the first time. We show that the nature of turbulence is highly compressible down to electron scales, particularly in the quasi-parallel magnetosheath. In this region, the magnetic turbulence also shows an inertial (Kolmogorov-like) range, indicating that the fluctuations are not formed locally, in contrast with the quasi-perpendicular magnetosheath. We also show that the electromagnetic turbulence is dominated by electric fluctuations at sub-ion scales (f > 1Hz) and that magnetic and electric spectra steepen at the largest-electron scale. The latter indicates a change in the nature of turbulence at electron scales. Finally, we show that the electric fluctuations around the electron gyrofrequency are mostly parallel in the quasi-perpendicular magnetosheath, where intense whistlers are observed. This result suggests that energy dissipation, plasma heating, and acceleration might be driven by intense electrostatic parallel structures/waves, which can be linked to whistler waves.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2018
Keywords
acceleration of particles, Earth, planets and satellites: magnetic fields, plasmas, turbulence waves
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-357380 (URN)10.3847/1538-4357/aabae8 (DOI)000433938500026 ()
Available from: 2018-08-24 Created: 2018-08-24 Last updated: 2018-08-31Bibliographically approved
Li, W. Y., André, M., Khotyaintsev, Y. V., Vaivads, A., Fuselier, S. A., Graham, D. B., . . . Burch, J. (2017). Cold Ionospheric Ions in the Magnetic Reconnection Outflow Region. Journal of Geophysical Research - Space Physics, 122(10), 10194-10202
Open this publication in new window or tab >>Cold Ionospheric Ions in the Magnetic Reconnection Outflow Region
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2017 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 10, p. 10194-10202Article in journal (Refereed) Published
Abstract [en]

Magnetosheath plasma usually determines properties of asymmetric magnetic reconnection at the subsolar region of Earth's magnetopause. However, cold plasma that originated from the ionosphere can also reach the magnetopause and modify the kinetic physics of asymmetric reconnection. We present a magnetopause crossing with high-density (10-60 cm(-3)) cold ions and ongoing reconnection from the observation of the Magnetospheric Multiscale (MMS) spacecraft. The magnetopause crossing is estimated to be 300 ion inertial lengths south of the X line. Two distinct ion populations are observed on the magnetosheath edge of the ion jet. One population with high parallel velocities (200-300 km/s) is identified to be cold ion beams, and the other population is the magnetosheath ions. In the deHoffman-Teller frame, the field-aligned magnetosheath ions are Alfvenic and move toward the jet region, while the field-aligned cold ion beams move toward the magnetosheath boundary layer, with much lower speeds. These cold ion beams are suggested to be from the cold ions entering the jet close to the X line. This is the first observation of the cold ionospheric ions in the reconnection outflow region, including the reconnection jet and the magnetosheath boundary layer.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2017
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-342096 (URN)10.1002/2017JA024287 (DOI)000419937800031 ()
Available from: 2018-03-02 Created: 2018-03-02 Last updated: 2018-03-02Bibliographically approved
Chasapis, A., Matthaeus, W. H., Parashar, T. N., LeContel, O., Retino, A., Breuillard, H., . . . Saito, Y. (2017). Electron Heating at Kinetic Scales in Magnetosheath Turbulence. Astrophysical Journal, 836(2), Article ID 247.
Open this publication in new window or tab >>Electron Heating at Kinetic Scales in Magnetosheath Turbulence
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2017 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 836, no 2, article id 247Article in journal (Refereed) Published
Abstract [en]

We present a statistical study of coherent structures at kinetic scales, using data from the Magnetospheric Multiscale mission in the Earth's magnetosheath. We implemented the multi-spacecraft partial variance of increments (PVI) technique to detect these structures, which are associated with intermittency at kinetic scales. We examine the properties of the electron heating occurring within such structures. We find that, statistically, structures with a high PVI index are regions of significant electron heating. We also focus on one such structure, a current sheet, which shows some signatures consistent with magnetic reconnection. Strong parallel electron heating coincides with whistler emissions at the edges of the current sheet.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2017
Keywords
acceleration of particles, magnetic reconnection, plasmas, turbulence
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-324354 (URN)10.3847/1538-4357/836/2/247 (DOI)000401169200015 ()
Available from: 2017-06-14 Created: 2017-06-14 Last updated: 2017-06-14Bibliographically approved
Toledo-Redondo, S., André, M., Khotyaintsev, Y. V., Lavraud, B., Vaivads, A., Graham, D. B., . . . Burch, J. L. (2017). Energy budget and mechanisms of cold ion heating in asymmetric magnetic reconnection. Journal of Geophysical Research - Space Physics, 122(9), 9396-9413
Open this publication in new window or tab >>Energy budget and mechanisms of cold ion heating in asymmetric magnetic reconnection
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2017 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 9, p. 9396-9413Article in journal (Refereed) Published
Abstract [en]

Cold ions (few tens of eV) of ionospheric origin are commonly observed on the magnetospheric side of the Earth's dayside magnetopause. As a result, they can participate in magnetic reconnection, changing locally the reconnection rate and being accelerated and heated. We present four events where cold ion heating was observed by the Magnetospheric Multiscale mission, associated with the magnetospheric Hall E field region of magnetic reconnection. For two of the events the cold ion density was small compared to the magnetosheath density, and the cold ions were heated roughly to the same temperature as magnetosheath ions inside the exhaust. On the other hand, for the other two events the cold ion density was comparable to the magnetosheath density and the cold ion heating observed was significantly smaller. Magnetic reconnection converts magnetic energy into particle energy, and ion heating is known to dominate the energy partition. We find that at least 10-25% of the energy spent by reconnection into ion heating went into magnetospheric cold ion heating. The total energy budget for cold ions may be even higher when properly accounting for the heavier species, namely helium and oxygen. Large E field fluctuations are observed in this cold ion heating region, i.e., gradients and waves, that are likely the source of particle energization.

Plain Language Summary: The magnetic field of Earth creates a natural shield that isolates and protects us from the particles and fields coming from our star, the Sun. This natural shield is called the magnetosphere and is filled by plasma. The particles coming from the Sun form another plasma called the solar wind and are usually deviated around the magnetosphere. However, under certain circumstances these two plasmas can reconnect (magnetic reconnection), and part of the energy and mass of the two plasmas is interchanged. Magnetic reconnection is the driver of storms and substorms inside the magnetosphere. In this work, we investigate what occurs to particles of very low energy (cold ions) of ionospheric origin when they reach the reconnecting boundary of the magnetosphere. It is found that they are energized and take an important part of the energy spent in reconnecting the plasmas. The plasma boundary develops spatial structures and emits waves that are able to heat the cold ions. Once heated, these cold ions irreversibly will escape the Earth's magnetosphere to never come back to Earth.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-340160 (URN)10.1002/2017JA024553 (DOI)000413491700021 ()
Available from: 2018-02-01 Created: 2018-02-01 Last updated: 2018-02-01Bibliographically approved
Khotyaintsev, Y. V., Divin, A., Vaivads, A., André, M. & Markidis, S. (2017). Energy conversion at dipolarization fronts. Geophysical Research Letters, 44(3), 1234-1242
Open this publication in new window or tab >>Energy conversion at dipolarization fronts
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2017 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, no 3, p. 1234-1242Article in journal (Refereed) Published
Abstract [en]

We use multispacecraft observations by Cluster in the Earth's magnetotail and 3-D particle-in-cell simulations to investigate conversion of electromagnetic energy at the front of a fast plasma jet. We find that the major energy conversion is happening in the Earth (laboratory) frame, where the electromagnetic energy is being transferred from the electromagnetic field to particles. This process operates in a region with size of the order several ion inertial lengths across the jet front, and the primary contribution to E . j is coming from the motional electric field and the ion current. In the frame of the front we find fluctuating energy conversion with localized loads and generators at sub-ion scales which are primarily related to the lower hybrid drift instability excited at the front; however, these provide relatively small net energy conversion.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2017
National Category
Astronomy, Astrophysics and Cosmology Geophysics
Identifiers
urn:nbn:se:uu:diva-319094 (URN)10.1002/2016GL071909 (DOI)000396115000006 ()
Funder
Swedish National Space Board, 136/11Swedish National Infrastructure for Computing (SNIC), 2014-8-38 SNIC 2016/1-457
Available from: 2017-04-03 Created: 2017-04-03 Last updated: 2017-11-29Bibliographically approved
Graham, D. B., Khotyaintsev, Y. V., Vaivads, A., Norgren, C., André, M., Webster, J. M., . . . Russell, C. T. (2017). Instability of Agyrotropic Electron Beams near the Electron Diffusion Region. Physical Review Letters, 119(2), Article ID 025101.
Open this publication in new window or tab >>Instability of Agyrotropic Electron Beams near the Electron Diffusion Region
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2017 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 119, no 2, article id 025101Article in journal (Refereed) Published
Abstract [en]

During a magnetopause crossing the Magnetospheric Multiscale spacecraft encountered an electron diffusion region (EDR) of asymmetric reconnection. The EDR is characterized by agyrotropic beam and crescent electron distributions perpendicular to the magnetic field. Intense upper-hybrid (UH) waves are found at the boundary between the EDR and magnetosheath inflow region. The UH waves are generated by the agyrotropic electron beams. The UH waves are sufficiently large to contribute to electron diffusion and scattering, and are a potential source of radio emission near the EDR. These results provide observational evidence of wave-particle interactions at an EDR, and suggest that waves play an important role in determining the electron dynamics.

National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-361237 (URN)10.1103/PhysRevLett.119.025101 (DOI)000405367800008 ()28753352 (PubMedID)
Funder
Swedish National Space Board, 175/15
Available from: 2018-09-26 Created: 2018-09-26 Last updated: 2018-09-26Bibliographically approved
Fu, H. S., Vaivads, A., Khotyaintsev, Y. V., André, M., Cao, J. B., Olshevsky, V., . . . Retino, A. (2017). Intermittent energy dissipation by turbulent reconnection. Geophysical Research Letters, 44(1), 37-43
Open this publication in new window or tab >>Intermittent energy dissipation by turbulent reconnection
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2017 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, no 1, p. 37-43Article in journal (Refereed) Published
Abstract [en]

Magnetic reconnectionthe process responsible for many explosive phenomena in both nature and laboratoryis efficient at dissipating magnetic energy into particle energy. To date, exactly how this dissipation happens remains unclear, owing to the scarcity of multipoint measurements of the diffusion region at the sub-ion scale. Here we report such a measurement by Clusterfour spacecraft with separation of 1/5 ion scale. We discover numerous current filaments and magnetic nulls inside the diffusion region of magnetic reconnection, with the strongest currents appearing at spiral nulls (O-lines) and the separatrices. Inside each current filament, kinetic-scale turbulence is significantly increased and the energy dissipation, Ej, is 100 times larger than the typical value. At the jet reversal point, where radial nulls (X-lines) are detected, the current, turbulence, and energy dissipations are surprisingly small. All these features clearly demonstrate that energy dissipation in magnetic reconnection occurs at O-lines but not X-lines.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2017
Keywords
turbulent reconnection, energy dissipation, turbulence, magnetic nulls, current filaments, intermittence
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-318611 (URN)10.1002/2016GL071787 (DOI)000393954900005 ()
Funder
Swedish Research Council
Available from: 2017-03-27 Created: 2017-03-27 Last updated: 2017-11-29Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-1654-841x

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