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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
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
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
Graham, D. B., Khotyaintsev, Y. V., Norgren, C., Vaivads, A., André, M., Toledo-Redondo, S., . . . Burch, J. L. (2017). Lower hybrid waves in the ion diffusion and magnetospheric inflow regions. Journal of Geophysical Research - Space Physics, 122(1), 517-533
Open this publication in new window or tab >>Lower hybrid waves in the ion diffusion and magnetospheric inflow regions
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2017 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 1, p. 517-533Article in journal (Refereed) Published
Abstract [en]

The role and properties of lower hybrid waves in the ion diffusion region and magnetospheric inflow region of asymmetric reconnection are investigated using the Magnetospheric Multiscale (MMS) mission. Two distinct groups of lower hybrid waves are observed in the ion diffusion region and magnetospheric inflow region, which have distinct properties and propagate in opposite directions along the magnetopause. One group develops near the ion edge in the magnetospheric inflow, where magnetosheath ions enter the magnetosphere through the finite gyroradius effect and are driven by the ion-ion cross-field instability due to the interaction between the magnetosheath ions and cold magnetospheric ions. This leads to heating of the cold magnetospheric ions. The second group develops at the sharpest density gradient, where the Hall electric field is observed and is driven by the lower hybrid drift instability. These drift waves produce cross-field particle diffusion, enabling magnetosheath electrons to enter the magnetospheric inflow region thereby broadening the density gradient in the ion diffusion region.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2017
Keywords
Magnetic reconnection, Ion diffusion region, Lower hybrid waves
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-319788 (URN)10.1002/2016JA023572 (DOI)000395655800038 ()
Funder
Swedish National Space Board
Available from: 2017-04-12 Created: 2017-04-12 Last updated: 2017-11-29Bibliographically approved
Voros, Z., Yordanova, E., Varsani, A., Genestreti, K. J., Khotyaintsev, Y. V., Li, W., . . . Saito, Y. (2017). MMS Observation of Magnetic Reconnection in the Turbulent Magnetosheath. Journal of Geophysical Research - Space Physics, 122(11), 11442-11467
Open this publication in new window or tab >>MMS Observation of Magnetic Reconnection in the Turbulent Magnetosheath
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2017 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 11, p. 11442-11467Article in journal (Refereed) Published
Abstract [en]

In this paper we use the full armament of the MMS (Magnetospheric Multiscale) spacecraft to study magnetic reconnection in the turbulent magnetosheath downstream of a quasi-parallel bow shock. Contrarily to the magnetopause and magnetotail cases, only a few observations of reconnection in the magnetosheath have been reported. The case study in this paper presents, for the first time, both fluid-scale and kinetic-scale signatures of an ongoing reconnection in the turbulent magnetosheath. The spacecraft are crossing the reconnection inflow and outflow regions and the ion diffusion region (IDR). Inside the reconnection outflows D shape ion distributions are observed. Inside the IDR mixing of ion populations, crescent-like velocity distributions and ion accelerations are observed. One of the spacecraft skims the outer region of the electron diffusion region, where parallel electric fields, energy dissipation/conversion, electron pressure tensor agyrotropy, electron temperature anisotropy, and electron accelerations are observed. Some of the difficulties of the observations of magnetic reconnection in turbulent plasma are also outlined.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2017
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-342091 (URN)10.1002/2017JA024535 (DOI)000419938600034 ()
Available from: 2018-03-01 Created: 2018-03-01 Last updated: 2018-03-02Bibliographically approved
Perri, S., Servidio, S., Vaivads, A. & Valentini, F. (2017). Numerical Study on the Validity of the Taylor Hypothesis in Space Plasmas. Astrophysical Journal Supplement Series, 231(1), Article ID 4.
Open this publication in new window or tab >>Numerical Study on the Validity of the Taylor Hypothesis in Space Plasmas
2017 (English)In: Astrophysical Journal Supplement Series, ISSN 0067-0049, E-ISSN 1538-4365, Vol. 231, no 1, article id 4Article in journal (Refereed) Published
Abstract [en]

In situ heliospheric measurements allow us to resolve fluctuations as a function of frequency. A crucial point is to describe the power spectral density as a function of the wavenumber, in order to understand the energy cascade through the scales in terms of plasma turbulence theories. The most favorable situation occurs when the average wind speed is much higher than the phase speed of the plasma modes, equivalent to the fact that the fluctuations' dynamical times are much longer than their typical crossing period through the spacecraft (frozen-in Taylor approximation). Using driven compressible Hall-magneothydrodynamics simulations, in which an "imaginary" spacecraft flies across a time-evolving turbulence, here we explore the limitations of the frozen-in assumption. We find that the Taylor hypothesis is robust down to sub-proton scales, especially for flows with mean velocities typical of the fast solar wind. For slow mean flows (i.e., speeds of the order of the Alfven speed) power spectra are subject to an amplitude shift throughout the scales. At small scales, when dispersive decorrelation mechanisms become significant, the frozen-in assumption is generally violated, in particular for k-vectors almost parallel to the average magnetic field. A discussion in terms of the spacetime autocorrelation function is proposed. These results might be relevant for the interpretation of the observations, in particular for existing and future space missions devoted to very high-resolution measurements.

Keywords
interplanetary medium, methods: numerical, plasmas, turbulence
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-341635 (URN)10.3847/1538-4365/aa755a (DOI)000415144100001 ()
Available from: 2018-02-12 Created: 2018-02-12 Last updated: 2018-02-12Bibliographically approved
Toledo-Redondo, S., André, M., Vaivads, A., Khotyaintsev, Y. V., Lavraud, B., Graham, D. B., . . . Aunai, N. (2016). Cold ion heating at the dayside magnetopause during magnetic reconnection. Geophysical Research Letters, 43(1), 58-66
Open this publication in new window or tab >>Cold ion heating at the dayside magnetopause during magnetic reconnection
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2016 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, no 1, p. 58-66Article in journal (Refereed) Published
Abstract [en]

Cold ions of ionospheric origin are known to be present in the magnetospheric side of the Earth's magnetopause. They can be very abundant, with densities up to 100cm(-3). These cold ions can mass load the magnetosphere, changing global parameters of magnetic reconnection, like the Alfven speed or the reconnection rate. In addition they introduce a new length scale related to their gyroradius and kinetic effects which must be accounted for. We report in situ observations of cold ion heating in the separatrix owing to time and space fluctuations of the electric field. When this occurs, the cold ions are preheated before crossing the Hall electric field barrier. However, when this mechanism is not present cold ions can be observed well inside the reconnection exhaust. Our observations suggest that the perpendicular cold ion heating is stronger close to the X line owing to waves and electric field gradients linked to the reconnection process.

Keywords
magnetic reconnection, cold ions, magnetopause
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-278013 (URN)10.1002/2015GL067187 (DOI)000369014100008 ()
Funder
Swedish Research Council, 621-2012-3280
Available from: 2016-02-23 Created: 2016-02-23 Last updated: 2017-11-30Bibliographically approved
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