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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
Keyword
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
Keyword
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
Keyword
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
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.

Keyword
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.

Keyword
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
Valentini, F., Perrone, D., Stabile, S., Pezzi, O., Servidio, S., De Marco, R., . . . Veltri, P. (2016). Differential kinetic dynamics and heating of ions in the turbulent solar wind. New Journal of Physics, 18, Article ID 125001.
Open this publication in new window or tab >>Differential kinetic dynamics and heating of ions in the turbulent solar wind
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2016 (English)In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 18, article id 125001Article in journal (Refereed) Published
Abstract [en]

The solar wind plasma is a fully ionized and turbulent gas ejected by the outer layers of the solar corona at very high speed, mainly composed by protons and electrons, with a small percentage of helium nuclei and a significantly lower abundance of heavier ions. Since particle collisions are practically negligible, the solar wind is typically not in a state of thermodynamic equilibrium. Such a complex system must be described through self-consistent and fully nonlinear models, taking into account its multi-species composition and turbulence. Weuse a kinetic hybrid Vlasov-Maxwell numerical code to reproduce the turbulent energy cascade down to ion kinetic scales, in typical conditions of the uncontaminated solar wind plasma, with the aim of exploring the differential kinetic dynamics of the dominant ion species, namely protons and alpha particles. Weshow that the response of different species to the fluctuating electromagnetic fields is different. In particular, a significant differential heating of alphas with respect to protons is observed. Interestingly, the preferential heating process occurs in spatial regions nearby the peaks of ion vorticity and where strong deviations from thermodynamic equilibrium are recovered. Moreover, by feeding a simulator of a top-hat ion spectrometer with the output of the kinetic simulations, we show that measurements by such spectrometer planned on board the Turbulence Heating ObserveR (THORmission), a candidate for the nextM4space mission of the European Space Agency, can provide detailed three-dimensional ion velocity distributions, highlighting important non-Maxwellian features. These results support the idea that future space missions will allow a deeper understanding of the physics of the interplanetary medium.

Keyword
solar wind, turbulence, plasma heating, space missions
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-313537 (URN)10.1088/1367-2630/18/12/125001 (DOI)000390356700001 ()
Available from: 2017-02-01 Created: 2017-01-20 Last updated: 2017-11-29Bibliographically approved
Graham, D. B., Khotyaintsev, Y. V., Norgren, C., Vaivads, A., André, M., Lindqvist, P.-A. -., . . . Burch, J. L. (2016). Electron currents and heating in the ion diffusion region of asymmetric reconnection. Geophysical Research Letters, 43(10), 4691-4700.
Open this publication in new window or tab >>Electron currents and heating in the ion diffusion region of asymmetric reconnection
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2016 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, no 10, p. 4691-4700Article in journal (Refereed) Published
Abstract [en]

In this letter the structure of the ion diffusion region of magnetic reconnection at Earth's magnetopause is investigated using the Magnetospheric Multiscale (MMS) spacecraft. The ion diffusion region is characterized by a strong DC electric field, approximately equal to the Hall electric field, intense currents, and electron heating parallel to the background magnetic field. Current structures well below ion spatial scales are resolved, and the electron motion associated with lower hybrid drift waves is shown to contribute significantly to the total current density. The electron heating is shown to be consistent with large-scale parallel electric fields trapping and accelerating electrons, rather than wave-particle interactions. These results show that sub-ion scale processes occur in the ion diffusion region and are important for understanding electron heating and acceleration.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-299741 (URN)10.1002/2016GL068613 (DOI)000378347500004 ()
Funder
Swedish National Space Board
Available from: 2016-07-26 Created: 2016-07-26 Last updated: 2017-11-28Bibliographically approved
Khotyaintsev, Y. V., Graham, D. B., Norgren, C., Eriksson, E., Li, W., Johlander, A., . . . Burch, J. L. (2016). Electron jet of asymmetric reconnection. Geophysical Research Letters, 43(11), 5571-5580.
Open this publication in new window or tab >>Electron jet of asymmetric reconnection
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2016 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, no 11, p. 5571-5580Article in journal (Refereed) Published
Abstract [en]

We present Magnetospheric Multiscale observations of an electron-scale current sheet and electron outflow jet for asymmetric reconnection with guide field at the subsolar magnetopause. The electron jet observed within the reconnection region has an electron Mach number of 0.35 and is associated with electron agyrotropy. The jet is unstable to an electrostatic instability which generates intense waves with E-vertical bar amplitudes reaching up to 300mVm(-1) and potentials up to 20% of the electron thermal energy. We see evidence of interaction between the waves and the electron beam, leading to quick thermalization of the beam and stabilization of the instability. The wave phase speed is comparable to the ion thermal speed, suggesting that the instability is of Buneman type, and therefore introduces electron-ion drag and leads to braking of the electron flow. Our observations demonstrate that electrostatic turbulence plays an important role in the electron-scale physics of asymmetric reconnection.

Keyword
magnetic reconnection, diffusion region, electron dynamics, lower hybrid waves, Buneman instability
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-301043 (URN)10.1002/2016GL069064 (DOI)000379851800005 ()
Funder
Swedish National Space Board, 139/12, 175/15
Available from: 2016-08-18 Created: 2016-08-17 Last updated: 2017-11-28Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-1654-841x

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