| 1. |
- Artemyev, A. V., et al.
(författare)
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Field-Aligned Currents Originating From the Magnetic Reconnection Region : Conjugate MMS-ARTEMIS Observations
- 2018
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 45:12, s. 5836-5844
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Tidskriftsartikel (refereegranskat)abstract
- Near-Earth magnetic reconnection reconfigures the magnetotail and produces strong plasma flows that transport plasma sheet particles and electromagnetic energy to the inner magnetosphere. An essential element of such a reconfiguration is strong, transient field-aligned currents. These currents, believed to be generated within the plasma sheet and closed at the ionosphere, are responsible for magnetosphere-ionosphere coupling during substorms. We use conjugate measurements from Magnetospheric Multiscale (MMS) at the plasma sheet boundary (around x approximate to- 10R(E)) and Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) at the equator (around x approximate to- 60R(E)) to explore the potential generation region of these currents. We find a clear correlation between the field-aligned current intensity measured by MMS and the tailward plasma sheet flows measured by ARTEMIS. To better understand the origin of this correlation, we compare spacecraft observations with results from 3-D particle-in-cell simulations of magnetotail reconnection. The comparison reveals that field-aligned currents and plasma flows start, wax, and wane due to the development of a reconnection region between MMS (near-Earth) and ARTEMIS (at lunar distance). A weak correlation between the field-aligned current intensity at MMS and earthward flow magnitudes at ARTEMIS suggests that distant magnetotail reconnection does not significantly contribute to the generation of the observed near-Earth currents. Our findings support the idea that the dominant role of the near-Earth magnetotail reconnection in the field-aligned current generation is likely responsible for their transient nature, whereas more steady distant tail reconnection would support long-term field-aligned current system. Plain Language Summary Field-aligned currents connect the Earth magnetotail and ionosphere, proving energy and information transport from the region where main energy release process, magnetic reconnection, occurs to the region where the collisional energy dissipation takes place. Therefore, investigation and modeling of the field-aligned current generation is important problem of the magnetosphere plasma physics. However, field-aligned current investigation requires simultaneous observations of reconnection signatures in the magnetotail and at high latitudes. Simultaneous and conjugate operation of two multispacecraft missions, Magnetospheric Multiscale and Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun, for the first time provide an opportunity for such investigation. Combining spacecraft observations with results from 3-D particle-in-cell simulations of magnetotail reconnection, we demonstrate that field-aligned currents and plasma flows start, wax, and wane due to the development of a reconnection region between near-Earth (Magnetospheric Multiscale location) and lunar distant tail (Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun location). Our findings support the idea that the dominant role of the near-Earth magnetotail reconnection in the field-aligned current generation is likely responsible for their transient nature, whereas more steady distant tail reconnection would support long-term field-aligned current system.
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| 2. |
- Breuillard, H., et al.
(författare)
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Multispacecraft analysis of dipolarization fronts and associated whistler wave emissions using MMS data
- 2016
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Ingår i: Geophysical Research Letters. - : Blackwell Publishing. - 0094-8276 .- 1944-8007. ; 43:14, s. 7279-7286
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Tidskriftsartikel (refereegranskat)abstract
- Dipolarization fronts (DFs), embedded in bursty bulk flows, play a crucial role in Earth's plasma sheet dynamics because the energy input from the solar wind is partly dissipated in their vicinity. This dissipation is in the form of strong low-frequency waves that can heat and accelerate energetic electrons up to the high-latitude plasma sheet. However, the dynamics of DF propagation and associated low-frequency waves in the magnetotail are still under debate due to instrumental limitations and spacecraft separation distances. In May 2015 the Magnetospheric Multiscale (MMS) mission was in a string-of-pearls configuration with an average intersatellite distance of 160km, which allows us to study in detail the microphysics of DFs. Thus, in this letter we employ MMS data to investigate the properties of dipolarization fronts propagating earthward and associated whistler mode wave emissions. We show that the spatial dynamics of DFs are below the ion gyroradius scale in this region (approximate to 500km), which can modify the dynamics of ions in the vicinity of the DF (e.g., making their motion nonadiabatic). We also show that whistler wave dynamics have a temporal scale of the order of the ion gyroperiod (a few seconds), indicating that the perpendicular temperature anisotropy can vary on such time scales.
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| 3. |
- Hietala, H., et al.
(författare)
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In Situ Observations of a Magnetosheath High-Speed Jet Triggering Magnetopause Reconnection
- 2018
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 45:4, s. 1732-1740
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Tidskriftsartikel (refereegranskat)abstract
- Magnetosheath high-speed jets-localized dynamic pressure enhancements typically of similar to 1 Earth radius in size-impact the dayside magnetopause several times per hour. Here we present the first in situ measurements suggesting that such an impact triggered magnetopause reconnection. We use observations from the five Time History of Events and Macroscale Interactions during Substorms spacecraft in a string-of-pearls configuration on 7 August 2007. The spacecraft recorded magnetopause in-and-out motion during an impact of a magnetosheath jet (V-N similar to -300km/s along the magnetopause normal direction). There was no evidence for reconnection for the preimpact crossing, yet three probes observed reconnection after the impact. We infer that the jet impact compressed the originally thick (60-70 d(i)), high magnetic shear (140-160 degrees magnetopause until it was thin enough for reconnection to occur. Magnetosheath high-speed jets could therefore act as a driver for bursty dayside reconnection.
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| 4. |
- Huang, S. Y., et al.
(författare)
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MMS observations of ion-scale magnetic island in the magnetosheath turbulent plasma
- 2016
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Ingår i: Geophysical Research Letters. - : Blackwell Publishing. - 0094-8276 .- 1944-8007. ; 43:15, s. 7850-7858
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Tidskriftsartikel (refereegranskat)abstract
- In this letter, first observations of ion-scale magnetic island from the Magnetospheric Multiscale mission in the magnetosheath turbulent plasma are presented. The magnetic island is characterized by bipolar variation of magnetic fields with magnetic field compression, strong core field, density depletion, and strong currents dominated by the parallel component to the local magnetic field. The estimated size of magnetic island is about 8 d(i), where d(i) is the ion inertial length. Distinct particle behaviors and wave activities inside and at the edges of the magnetic island are observed: parallel electron beam accompanied with electrostatic solitary waves and strong electromagnetic lower hybrid drift waves inside the magnetic island and bidirectional electron beams, whistler waves, weak electromagnetic lower hybrid drift waves, and strong broadband electrostatic noise at the edges of the magnetic island. Our observations demonstrate that highly dynamical, strong wave activities and electron-scale physics occur within ion-scale magnetic islands in the magnetosheath turbulent plasma.
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| 5. |
- Khotyaintsev, Yuri V., et al.
(författare)
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Electron jet of asymmetric reconnection
- 2016
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Ingår i: Geophysical Research Letters. - : Blackwell Publishing. - 0094-8276 .- 1944-8007. ; 43:11, s. 5571-5580
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
- Le Contel, O., et al.
(författare)
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Whistler mode waves and Hall fields detected by MMS during a dayside magnetopause crossing
- 2016
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Ingår i: Geophysical Research Letters. - : Blackwell Publishing. - 0094-8276 .- 1944-8007. ; 43:12, s. 5943-5952
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Tidskriftsartikel (refereegranskat)abstract
- We present Magnetospheric Multiscale (MMS) mission measurements during a full magnetopause crossing associated with an enhanced southward ion flow. A quasi-steady magnetospheric whistler mode wave emission propagating toward the reconnection region with quasi-parallel and oblique wave angles is detected just before the opening of the magnetic field lines and the detection of escaping energetic electrons. Its source is likely the perpendicular temperature anisotropy of magnetospheric energetic electrons. In this region, perpendicular and parallel currents as well as the Hall electric field are calculated and found to be consistent with the decoupling of ions from the magnetic field and the crossing of a magnetospheric separatrix region. On the magnetosheath side, Hall electric fields are found smaller as the density is larger but still consistent with the decoupling of ions. Intense quasi-parallel whistler wave emissions are detected propagating both toward and away from the reconnection region in association with a perpendicular anisotropy of the high-energy part of the magnetosheath electron population and a strong perpendicular current, which suggests that in addition to the electron diffusion region, magnetosheath separatrices could be a source region for whistler waves.
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| 7. |
- Li, Wenya, et al.
(författare)
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Upper-Hybrid Waves Driven by Meandering Electrons Around Magnetic Reconnection X Line
- 2021
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 48:16
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic reconnection is a fundamental process in collisionless space plasma environment, and plasma waves relevant to the kinetic interactions can have a significant impact on the multiscale behavior of reconnection. Here, we present Magnetospheric Multiscale (MMS) observations during an encounter of an X line of symmetric magnetic reconnection in the magnetotail. The X line is characterized by reversals of ion and electron jets and electromagnetic fields, agyrotropic electron velocity distribution functions (VDFs), and an electron-scale current sheet. MMS observe large-amplitude nonlinear upper-hybrid (UH) waves on both sides of the neutral line, and the wave amplitudes have highly localized distribution along the normal direction. The inbound meandering electrons drive the UH waves, releasing the free energy stored from the reconnection electric field along the meandering trajectories. The interaction between the meandering electrons and the UH waves may modify the balance of the reconnection electric field around the X line. Plain Language Summary The electron-scale kinetic physics in the electron diffusion region (EDR) controls how magnetic field lines break and reconnect. Electron crescent, an indicator of EDR, can drive high-frequency electrostatic waves around EDR. For the first time, the upper-hybrid (UH) waves are observed on both sides of the X line and we show the direct association between the UH waves and the reconnection electric field. The strong wave-electron interaction can change the electron-scale dynamics and may modify the reconnection electric field. This study demonstrates that the UH waves may play an important role in controlling the reconnection rate.
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| 8. |
- Nakamura, R., et al.
(författare)
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Transient, small-scale field-aligned currents in the plasma sheet boundary layer during storm time substorms
- 2016
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 43:10, s. 4841-4849
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Tidskriftsartikel (refereegranskat)abstract
- We report on field-aligned current observations by the four Magnetospheric Multiscale (MMS) spacecraft near the plasma sheet boundary layer (PSBL) during two major substorms on 23 June 2015. Small-scale field-aligned currents were found embedded in fluctuating PSBL flux tubes near the separatrix region. We resolve, for the first time, short-lived earthward (downward) intense field-aligned current sheets with thicknesses of a few tens of kilometers, which are well below the ion scale, on flux tubes moving equatorward/earthward during outward plasma sheet expansion. They coincide with upward field-aligned electron beams with energies of a few hundred eV. These electrons are most likely due to acceleration associated with a reconnection jet or high-energy ion beam-produced disturbances. The observations highlight coupling of multiscale processes in PSBL as a consequence of magnetotail reconnection.
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| 9. |
- Wilder, F. D., et al.
(författare)
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Observations of large-amplitude, parallel, electrostatic waves associated with the Kelvin-Helmholtz instability by the magnetospheric multiscale mission
- 2016
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Ingår i: Geophysical Research Letters. - : Blackwell Publishing. - 0094-8276 .- 1944-8007. ; 43:17, s. 8859-8866
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Tidskriftsartikel (refereegranskat)abstract
- On 8 September 2015, the four Magnetospheric Multiscale spacecraft encountered a Kelvin-Helmholtz unstable magnetopause near the dusk flank. The spacecraft observed periodic compressed current sheets, between which the plasma was turbulent. We present observations of large-amplitude (up to 100 mV/m) oscillations in the electric field. Because these oscillations are purely parallel to the background magnetic field, electrostatic, and below the ion plasma frequency, they are likely to be ion acoustic-like waves. These waves are observed in a turbulent plasma where multiple particle populations are intermittently mixed, including cold electrons with energies less than 10 eV. Stability analysis suggests a cold electron component is necessary for wave growth.
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| 10. |
- Wilder, F. D., et al.
(författare)
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Observations of whistler mode waves with nonlinear parallel electric fields near the dayside magnetic reconnection separatrix by the Magnetospheric Multiscale mission
- 2016
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Ingår i: Geophysical Research Letters. - : Blackwell Publishing. - 0094-8276 .- 1944-8007. ; 43:12, s. 5909-5917
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Tidskriftsartikel (refereegranskat)abstract
- We show observations from the Magnetospheric Multiscale (MMS) mission of whistler mode waves in the Earth's low-latitude boundary layer (LLBL) during a magnetic reconnection event. The waves propagated obliquely to the magnetic field toward the X line and were confined to the edge of a southward jet in the LLBL. Bipolar parallel electric fields interpreted as electrostatic solitary waves (ESW) are observed intermittently and appear to be in phase with the parallel component of the whistler oscillations. The polarity of the ESWs suggests that if they propagate with the waves, they are electron enhancements as opposed to electron holes. The reduced electron distribution shows a shoulder in the distribution for parallel velocities between 17,000 and 22,000 km/s, which persisted during the interval when ESWs were observed, and is near the phase velocity of the whistlers. This shoulder can drive Langmuir waves, which were observed in the high-frequency parallel electric field data.
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