uu.seUppsala University Publications
Change search
Link to record
Permanent link

Direct link
BETA
Alternative names
Publications (10 of 133) Show all publications
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
Show others...
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
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
Show others...
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
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
Show others...
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
Graham, D. B., Vaivads, A., Khotyaintsev, Y. V., Eriksson, A., André, M., Malaspina, D. M., . . . Plaschke, F. (2018). Enhanced Escape of Spacecraft Photoelectrons Caused by Langmuir and Upper Hybrid Waves. Journal of Geophysical Research - Space Physics, 123(9), 7534-7553
Open this publication in new window or tab >>Enhanced Escape of Spacecraft Photoelectrons Caused by Langmuir and Upper Hybrid Waves
Show others...
2018 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 9, p. 7534-7553Article in journal (Refereed) Published
Abstract [en]

The spacecraft potential is often used to infer rapid changes in the thermal plasma density. The variations in spacecraft potential associated with large-amplitude Langmuir and upper hybrid waves are investigated with the Magnetospheric Multiscale (MMS) mission. When large-amplitude Langmuir and upper hybrid waves are observed, the spacecraft potential increases. The changes in spacecraft potential are shown to be due to enhanced photoelectron escape from the spacecraft when the wave electric fields reach large amplitude. The fluctuations in spacecraft potential follow the envelope function of the Langmuir and upper hybrid waves. Comparison with the high-resolution electron moments shows that the changes in spacecraft potential associated with the waves are not due to density perturbations. Indeed, using the spacecraft potential as a density probe leads to unphysically large density fluctuations. In addition, the changes in spacecraft potential are shown to increase as density decreases: larger spacecraft potential changes are observed in the magnetosphere, than in the magnetosheath and solar wind. These results show that external electric fields can lead to unphysical results when the spacecraft potential is used as a density probe. The results suggest that fluctuations in the spacecraft potential alone cannot be used to determine whether nonlinear processes associated with Langmuir and upper hybrid waves, such as the ponderomotive force and three-wave decay, are occurring.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2018
Keywords
Langmuir waves, photoelectron current, spacecraft potential, upper hybrid waves
National Category
Fusion, Plasma and Space Physics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-369520 (URN)10.1029/2018JA025874 (DOI)000448376600029 ()
Funder
Swedish National Space Board, 175/15Swedish National Space Board, 128/17
Available from: 2018-12-17 Created: 2018-12-17 Last updated: 2018-12-17Bibliographically approved
Schwartz, S. J., Avanov, L., Turner, D., Zhang, H., Gingell, I., Eastwood, J. P., . . . Wilder, F. (2018). Ion Kinetics in a Hot Flow Anomaly: MMS Observations. Geophysical Research Letters, 45(21), 11520-11529
Open this publication in new window or tab >>Ion Kinetics in a Hot Flow Anomaly: MMS Observations
Show others...
2018 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 21, p. 11520-11529Article in journal (Refereed) Published
Abstract [en]

Hot Flow Anomalies (HFAs) are transients observed at planetary bow shocks, formed by the shock interaction with a convected interplanetary current sheet. The primary interpretation relies on reflected ions channeled upstream along the current sheet. The short duration of HFAs has made direct observations of this process difficult. We employ high resolution measurements by NASA's Magnetospheric Multiscale Mission to probe the ion microphysics within a HFA. Magnetospheric Multiscale Mission data reveal a smoothly varying internal density and pressure, which increase toward the trailing edge of the HFA, sweeping up particles trapped within the current sheet. We find remnants of reflected or other backstreaming ions traveling along the current sheet, but most of these are not fast enough to out-run the incident current sheet convection. Despite the high level of internal turbulence, incident and backstreaming ions appear to couple gyro-kinetically in a coherent manner. Plain Language Summary Shock waves in space are responsible for energizing particles and diverting supersonic flows around planets and other obstacles. Explosive events known as Hot Flow Anomalies (HFAs) arise when a rapid change in the interplanetary magnetic field arrives at the bow shock formed by, for example, the supersonic solar wind plasma flow from the Sun impinging on the Earth's magnetic environment. HFAs are known to produce impacts all the way to ground level, but the physics responsible for their formation occur too rapidly to be resolved by previous satellite missions. This paper employs NASA's fleet of four Magnetospheric Multiscale satellites to reveal for the first time clear, discreet populations of ions that interact coherently to produce the extreme heating and deflection.

National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-372713 (URN)10.1029/2018GL080189 (DOI)000451832600002 ()
Available from: 2019-01-08 Created: 2019-01-08 Last updated: 2019-01-08Bibliographically 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
Show others...
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
Show others...
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
Alm, L., André, M., Vaivads, A., Khotyaintsev, Y. V., Torbert, R. B., Burch, J. L., . . . Mauk, B. H. (2018). Magnetotail Hall Physics in the Presence of Cold Ions. Geophysical Research Letters, 45(20), 10941-10950
Open this publication in new window or tab >>Magnetotail Hall Physics in the Presence of Cold Ions
Show others...
2018 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 20, p. 10941-10950Article in journal (Refereed) Published
Abstract [en]

We present the first in situ observation of cold ionospheric ions modifying the Hall physics of magnetotail reconnection. While in the tail lobe, Magnetospheric Multiscale mission observed cold (tens of eV) E x B drifting ions. As Magnetospheric Multiscale mission crossed the separatrix of a reconnection exhaust, both cold lobe ions and hot (keV) ions were observed. During the closest approach of the neutral sheet, the cold ions accounted for similar to 30% of the total ion density. Approximately 65% of the initial cold ions remained cold enough to stay magnetized. The Hall electric field was mainly supported by the j x B term of the generalized Ohm's law, with significant contributions from the del center dot P-e and v(c) x B terms. The results show that cold ions can play an important role in modifying the Hall physics of magnetic reconnection even well inside the plasma sheet. This indicates that modeling magnetic reconnection may benefit from including multiscale Hall physics. Plain Language Summary Cold ions have the potential of changing the fundamental physics behind magnetic reconnection. Here we present the first direct observation of this process in action in the magnetotail. Cold ions from the tail lobes were able to remain cold even deep inside the much hotter plasma sheet. Even though the cold ions only accounted for similar to 30% of the total ions, they had a significant impact on the electric fields near the reconnection region.

National Category
Geophysics Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-372422 (URN)10.1029/2018GL079857 (DOI)000451510500017 ()
Funder
Swedish National Space Board, SNSB 176/15Swedish National Space Board, 158/16
Available from: 2019-01-07 Created: 2019-01-07 Last updated: 2019-01-07Bibliographically 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
Show others...
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
Pan, D.-X., Khotyaintsev, Y. V., Graham, D. B., Vaivads, A., Zhou, X.-Z., André, M., . . . Burch, J. L. (2018). Rippled Electron-Scale Structure of a Dipolarization Front. Geophysical Research Letters, 45(22), 12116-12124
Open this publication in new window or tab >>Rippled Electron-Scale Structure of a Dipolarization Front
Show others...
2018 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 22, p. 12116-12124Article in journal (Refereed) Published
Abstract [en]

We use the Magnetospheric Multiscale mission to investigate electron-scale structures at a dipolarization front. The four spacecraft are separated by electron scales and observe large differences in plasma and field parameters within the dipolarization front, indicating strong deviation from typically assumed plane or slightly curved front surface. We attribute this to ripples generated by the lower hybrid drift instability (LHDI) with wave number of k(rho e)similar or equal to 0.4 and maximum wave potential of similar to 1 kV similar to k(B)T(e). Power law-like spectra of E-perpendicular to with slope of -3 indicates the turbulent cascade of LHDI. LHDI is observed together with bursty high-frequency parallel electric fields, suggesting coupling of LHDI to higher-frequency electrostatic waves. Plain Language Summary Dipolarization fronts (DFs) are narrow boundaries with sharp enhancement of magnetic field, located at the leading part of fast plasma jets observed in Earth's magnetotail. DFs are typically assumed to be smooth boundaries at scales comparable to the ion gyroradius and below. In this study, we use the four Magnetospheric Multiscale spacecraft separated by several electron gyroradii to investigate fine structure of a DF. Surprisingly, we observe significant differences in the fields and plasma measurements between the spacecraft despite their small separation. We attribute these signatures to electron-scale disturbances propagating along the DF surface, and thus the DF surface is not smooth as expected but rather rippled. The ripples develop as a result of a plasma instability driven by the strong inhomogeneities present at the DF. The fact that the ripples have such small scales means that they can effectively interact with plasma electrons.

Keywords
dipolarization fronts, LHDI, ripples, electron-scale structures, MMS, turbulence
National Category
Fusion, Plasma and Space Physics Geophysics
Identifiers
urn:nbn:se:uu:diva-373246 (URN)10.1029/2018GL080826 (DOI)000453250000003 ()
Funder
Swedish Research Council, 2016-05507Swedish National Space Board, 128/17
Available from: 2019-01-14 Created: 2019-01-14 Last updated: 2019-01-14Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-1654-841x

Search in DiVA

Show all publications