| 1. |
- Fu, H. S., et al.
(författare)
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Identifying magnetic reconnection events using the FOTE method
- 2016
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 121:2, s. 1263-1272
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Tidskriftsartikel (refereegranskat)abstract
- A magnetic reconnection event detected by Cluster is analyzed using three methods: Single-spacecraft Inference based on Flow-reversal Sequence (SIFS), Multispacecraft Inference based on Timing a Structure (MITS), and the First-Order Taylor Expansion (FOTE). Using the SIFS method, we find that the reconnection structure is an X line; while using the MITS and FOTE methods, we find it is a magnetic island (O line). We compare the efficiency and accuracy of these three methods and find that the most efficient and accurate approach to identify a reconnection event is FOTE. In both the guide and nonguide field reconnection regimes, the FOTE method is equally applicable. This study for the first time demonstrates the capability of FOTE in identifying magnetic reconnection events; it would be useful to the forthcoming Magnetospheric Multiscale (MMS) mission. ion
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| 2. |
- Huang, S. Y., et al.
(författare)
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Magnetospheric Multiscale Observations of Electron Vortex Magnetic Hole in the Turbulent Magnetosheath Plasma
- 2017
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Ingår i: Astrophysical Journal Letters. - : Institute of Physics Publishing. - 2041-8205 .- 2041-8213. ; 836:2
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Tidskriftsartikel (refereegranskat)abstract
- We report on the observations of an electron vortex magnetic hole corresponding to a new type of coherent structure in the turbulent magnetosheath plasma using the Magnetospheric Multiscale mission data. The magnetic hole is characterized by a magnetic depression, a density peak, a total electron temperature increase (with a parallel temperature decrease but a perpendicular temperature increase), and strong currents carried by the electrons. The current has a dip in the core region and a peak in the outer region of the magnetic hole. The estimated size of the magnetic hole is about 0.23 ρi (∼30 ρe) in the quasi-circular cross-section perpendicular to its axis, where ρi and ρe are respectively the proton and electron gyroradius. There are no clear enhancements seen in high-energy electron fluxes. However, there is an enhancement in the perpendicular electron fluxes at 90° pitch angle inside the magnetic hole, implying that the electrons are trapped within it. The variations of the electron velocity components Vem and Ven suggest that an electron vortex is formed by trapping electrons inside the magnetic hole in the cross-section in the M-N plane. These observations demonstrate the existence of a new type of coherent structures behaving as an electron vortex magnetic hole in turbulent space plasmas as predicted by recent kinetic simulations.
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| 3. |
- Lavraud, B., et al.
(författare)
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Currents and associated electron scattering and bouncing near the diffusion region at Earth's magnetopause
- 2016
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 43:7, s. 3042-3050
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Tidskriftsartikel (refereegranskat)abstract
- Based on high-resolution measurements from NASA's Magnetospheric Multiscale mission, we present the dynamics of electrons associated with current systems observed near the diffusion region of magnetic reconnection at Earth's magnetopause. Using pitch angle distributions (PAD) and magnetic curvature analysis, we demonstrate the occurrence of electron scattering in the curved magnetic field of the diffusion region down to energies of 20 eV. We show that scattering occurs closer to the current sheet as the electron energy decreases. The scattering of inflowing electrons, associated with field-aligned electrostatic potentials and Hall currents, produces a new population of scattered electrons with broader PAD which bounce back and forth in the exhaust. Except at the center of the diffusion region the two populations are collocated and appear to behave adiabatically: the inflowing electron PAD focuses inward (toward lower magnetic field), while the bouncing population PAD gradually peaks at 90 degrees away from the center (where it mirrors owing to higher magnetic field and probable field-aligned potentials).
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| 4. |
- Le Contel, O., et al.
(författare)
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Lower Hybrid Drift Waves and Electromagnetic Electron Space-Phase Holes Associated With Dipolarization Fronts and Field-Aligned Currents Observed by the Magnetospheric Multiscale Mission During a Substorm
- 2017
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Ingår i: Journal of Geophysical Research - Space Physics. - : AMER GEOPHYSICAL UNION. - 2169-9380 .- 2169-9402. ; 122:12, s. 12236-12257
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Tidskriftsartikel (refereegranskat)abstract
- We analyze two ion scale dipolarization fronts associated with field-aligned currents detected by the Magnetospheric Multiscale mission during a large substorm on 10 August 2016. The first event corresponds to a fast dawnward flow with an antiparallel current and could be generated by the wake of a previous fast earthward flow. It is associated with intense lower hybrid drift waves detected at the front and propagating dawnward with a perpendicular phase speed close to the electric drift and the ion thermal velocity. The second event corresponds to a flow reversal: from southwward/dawnward to northward/duskward associated with a parallel current consistent with a brief expansion of the plasma sheet before the front crossing and with a smaller lower hybrid drift wave activity. Electromagnetic electron phase-space holes are detected near these low-frequency drift waves during both events. The drift waves could accelerate electrons parallel to the magnetic field and produce the parallel electron drift needed to generate the electron holes. Yet we cannot rule out the possibility that the drift waves are produced by the antiparallel current associated with the fast flows, leaving the source for the electron holes unexplained.
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| 5. |
- Peng, F. Z., et al.
(författare)
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Quadrupolar pattern of the asymmetric guide-field reconnection
- 2017
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 122:6, s. 6349-6356
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Tidskriftsartikel (refereegranskat)abstract
- With high-resolution data of the recently launched Magnetospheric Multiscale mission, we report a magnetic reconnection event at the dayside magnetopause. This reconnection event, having a density asymmetry N-high/N-low approximate to 2 on the two sides of the reconnecting current sheet and a guide field B-g approximate to 0.4B(0) in the out-of-plane direction, exhibit all the two-fluid features: Alfvenic plasma jets in the outflow region, bipolar Hall electric fields toward the current sheet center, quadrupolar Hall magnetic fields in the out-of-plane direction, and the corresponding Hall currents. Obviously, the density asymmetry N-high/N-low approximate to 2 and the guide field B-g approximate to 0.4B(0) are not sufficient to dismiss the quadrupolar pattern of Hall reconnection. This is different from previous simulations, where the bipolar pattern of Hall reconnection was suggested.
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| 6. |
- Voros, Z., et al.
(författare)
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MMS Observation of Magnetic Reconnection in the Turbulent Magnetosheath
- 2017
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Ingår i: Journal of Geophysical Research - Space Physics. - : AMER GEOPHYSICAL UNION. - 2169-9380 .- 2169-9402. ; 122:11, s. 11442-11467
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
- Yordanova, Emiliya, et al.
(författare)
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Electron scale structures and magnetic reconnection signatures in the turbulent magnetosheath
- 2016
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Ingår i: Geophysical Research Letters. - : Blackwell Publishing. - 0094-8276 .- 1944-8007. ; 43:12, s. 5969-5978
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Tidskriftsartikel (refereegranskat)abstract
- Collisionless space plasma turbulence can generate reconnecting thin current sheets as suggested by recent results of numerical magnetohydrodynamic simulations. The Magnetospheric Multiscale (MMS) mission provides the first serious opportunity to verify whether small ion-electron-scale reconnection, generated by turbulence, resembles the reconnection events frequently observed in the magnetotail or at the magnetopause. Here we investigate field and particle observations obtained by the MMS fleet in the turbulent terrestrial magnetosheath behind quasi-parallel bow shock geometry. We observe multiple small-scale current sheets during the event and present a detailed look of one of the detected structures. The emergence of thin current sheets can lead to electron scale structures. Within these structures, we see signatures of ion demagnetization, electron jets, electron heating, and agyrotropy suggesting that MMS spacecraft observe reconnection at these scales.
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| 8. |
- Zhou, M., et al.
(författare)
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Sub-ion-scale Dynamics of the Ion Diffusion Region in the Magnetotail : MMS Observations
- 2019
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Ingår i: Journal of Geophysical Research - Space Physics. - : AMER GEOPHYSICAL UNION. - 2169-9380 .- 2169-9402. ; 124:10, s. 7898-7911
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports magnetospheric multiscale (MMS) observations of the sub-ion-scale dynamics within the ion diffusion region (IDR) in the Earth's magnetotail. MMS crossed the IDR from the southern to the northern hemisphere, at about two ion inertial length earthward of the X line with a small guide field. Electrons were anisotropic in the inflow region of the IDR and turned into isotropic within the IDR. The isotropization of the electrons was probably due to the pitch angle scattering in highly curved magnetic field lines. We suggest that the thickness of the electron isotropic region strongly depends on the horizontal distance to the X line. The out-of-plane current bifurcated in the IDR. It peaked at the boundaries between the inflow and outflow electrons around the separatrices. Magnetic energy conversion and dissipation predominantly occurred at the peak of the out-of-plane current instead of at the neutral sheet center where B-L = 0. Both the energy dissipation and normal electric field E-N exhibited evident asymmetry with respect to the neutral sheet. The energy dissipation was larger around the northern separatrix than around the southern separatrix. The electric field E-N showed a tripolar variation across the neutral sheet, that is, a unipolar E-N around the southern separatrix and a bipolar E-N around the northern separatrix. The reasons and implications of these asymmetries are discussed.
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| 9. |
- André, Mats, et al.
(författare)
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Magnetic reconnection and modification of the Hall physics due to cold ions at the magnetopause
- 2016
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Ingår i: Geophysical Research Letters. - : Blackwell Publishing. - 0094-8276 .- 1944-8007. ; 43:13, s. 6705-6712
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Tidskriftsartikel (refereegranskat)abstract
- Observations by the four Magnetospheric Multiscale spacecraft are used to investigate the Hall physics of a magnetopause magnetic reconnection separatrix layer. Inside this layer of currents and strong normal electric fields, cold (eV) ions of ionospheric origin can remain frozen-in together with the electrons. The cold ions reduce the Hall current. Using a generalized Ohm's law, the electric field is balanced by the sum of the terms corresponding to the Hall current, the vxB drifting cold ions, and the divergence of the electron pressure tensor. A mixture of hot and cold ions is common at the subsolar magnetopause. A mixture of length scales caused by a mixture of ion temperatures has significant effects on the Hall physics of magnetic reconnection.
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| 10. |
- Breuillard, H., et al.
(författare)
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New Insights into the Nature of Turbulence in the Earth's Magnetosheath Using Magnetospheric MultiScale Mission Data
- 2018
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Ingår i: Astrophysical Journal. - : IOP PUBLISHING LTD. - 0004-637X .- 1538-4357. ; 859:2
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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