| 1. |
- Ergun, R. E., et al.
(författare)
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Magnetospheric Multiscale observations of large-amplitude, parallel, electrostatic waves associated with magnetic reconnection at the magnetopause
- 2016
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Ingår i: Geophysical Research Letters. - : Blackwell Publishing. - 0094-8276 .- 1944-8007. ; 43:11, s. 5626-5634
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Tidskriftsartikel (refereegranskat)abstract
- We report observations from the Magnetospheric Multiscale satellites of large-amplitude, parallel, electrostatic waves associated with magnetic reconnection at the Earth's magnetopause. The observed waves have parallel electric fields (E-||) with amplitudes on the order of 100mV/m and display nonlinear characteristics that suggest a possible net E-||. These waves are observed within the ion diffusion region and adjacent to (within several electron skin depths) the electron diffusion region. They are in or near the magnetosphere side current layer. Simulation results support that the strong electrostatic linear and nonlinear wave activities appear to be driven by a two stream instability, which is a consequence of mixing cold (<10eV) plasma in the magnetosphere with warm (similar to 100eV) plasma from the magnetosheath on a freshly reconnected magnetic field line. The frequent observation of these waves suggests that cold plasma is often present near the magnetopause.
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| 2. |
- Han, D. -S, et al.
(författare)
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Coordinated observations of two types of diffuse auroras near magnetic local noon by Magnetospheric Multiscale mission and ground all-sky camera
- 2017
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 44:16, s. 8130-8139
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Tidskriftsartikel (refereegranskat)abstract
- Structured diffuse auroras are often observed near magnetic local noon (MLN), but their generation mechanisms are poorly understood. We have found that two types of structured diffuse auroras with obviously different dynamical properties often coexist near MLN. One type usually drifts from low to high latitude with higher speed and shows pulsation. The other type is always adjacent to the discrete aurora oval and drifts together with nearby discrete aurora with much lower speed. Using coordinated observations from MMS and ground all-sky imagers, we found that the two types of diffuse auroras are well correlated with number density increase of O+ (from the ionosphere) and of He2+ (from magnetosheath) ions, respectively. These observations indicate that mangetosheath particles penetrated into the magnetosphere also can play an important role for producing the dayside diffuse aurora. In addition, for the first time, electron cyclotron harmonic waves are observed associated with dayside diffuse aurora.
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| 3. |
- Huang, S. Y., et al.
(författare)
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Electron acceleration in the reconnection diffusion region : Cluster observations
- 2012
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Ingår i: Geophysical Research Letters. - : Blackwell Publishing. - 0094-8276 .- 1944-8007. ; 39:L11103
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Tidskriftsartikel (refereegranskat)abstract
- We present one case study of magnetic islands and energetic electrons in the reconnection diffusion region observed by the Cluster spacecraft. The cores of the islands are characterized by strong core magnetic fields and density depletion. Intense currents, with the dominant component parallel to the ambient magnetic field, are detected inside the magnetic islands. A thin current sheet is observed in the close vicinity of one magnetic island. Energetic electron fluxes increase at the location of the thin current sheet, and further increase inside the magnetic island, with the highest fluxes located at the core region of the island. We suggest that these energetic electrons are firstly accelerated in the thin current sheet, and then trapped and further accelerated in the magnetic island by betatron and Fermi acceleration.
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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. |
- Huang, S. Y., et al.
(författare)
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Observations of Flux Ropes With Strong Energy Dissipation in the Magnetotail
- 2019
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 46:2, s. 580-589
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Tidskriftsartikel (refereegranskat)abstract
- An ion-scale flux rope (FR), embedded in a high-speed electron flow (possibly an electron vortex), is investigated in the magnetotail using observations from the Magnetospheric Multiscale (MMS) spacecraft. Intense electric field and current and abundant waves are observed in the exterior and interior regions of the FR. Comparable parallel and perpendicular currents in the interior region imply that the FR has a non-force-free configuration. Electron demagnetization occurs in some subregions of the FR. It is surprising that strong dissipation (I x E' up to 2,000 pW/m(3)) occurs in the center of the FR without signatures of secondary reconnection or coalescence of two FRs, implying that FR may provide another important channel for energy dissipation in space plasmas. These features indicate that the observed FR is still highly dynamical, and hosts multiscale coupling processes, even though the FR has a very large scale and is far away from the reconnection site. Plain Language Summary: Flux ropes, 3-D helical magnetic structures, in which magnetic field lines twist with each other, play an important role in the macroscopic and microscopic physical process during magnetic reconnection. Most of previous studies focused on the flux ropes in the reconnection region. However, some physical process inside macroscopic flux ropes far away from the reconnection site in the magnetotail is still unclear due to the lack of high time resolution data. In this letter, thanks to the unprecedented high time resolution data of the Magnetospheric Multiscale (MMS) mission, we report an ion-scale flux rope and study its dynamics. Our observations demonstrate that the observed flux rope is still highly dynamical, and hosting multiscale coupling processes and strong energy dissipation, even though the flux rope has very large scale and is far away from the reconnection site.
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| 6. |
- Huang, S. Y., et al.
(författare)
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Observations of turbulence within reconnection jet in the presence of guide field
- 2012
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Ingår i: Geophysical Research Letters. - : Blackwell Publishing. - 0094-8276 .- 1944-8007. ; 39:L11104
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Tidskriftsartikel (refereegranskat)abstract
- We present the first comprehensive observations of turbulence properties within high speed reconnection jet in the plasma sheet with moderate guide field. The power spectral density index is about -1.73 in the inertial range, and follows the value of -2.86 in the ion dissipation range. The turbulence is strongly anisotropic in the wave-vector space with the major power having its wave-vector highly oblique to the ambient magnetic field, suggesting that the turbulence is quasi-2D. The measured "dispersion relations" obtained using the k-filtering technique are compared with theory and are found to be consistent with the Alfven-Whistler mode. In addition, both Probability Distribution Functions and flatness results show that the turbulence in the reconnection jet is intermittent (multifractal) at scales less than the proton gyroradius/inertial lengths. The estimated electric field provided by anomalous resistivity caused by turbulence is about 3 mV/m, which is close to the typical reconnection electric field in the magnetotail.
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| 7. |
- Man, H. Y., et al.
(författare)
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In Situ Observation of Magnetic Reconnection Between an Earthward Propagating Flux Rope and the Geomagnetic Field
- 2018
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 45:17, s. 8729-8737
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Tidskriftsartikel (refereegranskat)abstract
- It has been proposed that, in the near-Earth magnetotail, earthward propagating flux ropes can merge with the Earth's dipole magnetic field and dissipate its magnetic energy. However, the reconnection diffusion region related to this process has not been identified. Here we report the first in situ observation of magnetic reconnection between an earthward propagating flux rope and the closed magnetic field lines connecting to Earth. Magnetospheric Multiscale (MMS) spacecraft crossed a vertical current sheet between the leading edge of the flux rope (negative B-Z) and the geomagnetic field (positive B-Z). The subion-scale current sheet, super-Alfvenic electron outflow, Hall magnetic and electric field, conversion of magnetic energy to plasma energy (J.E > 0), and magnetic null were observed during the crossing. All the above signatures indicate that MMS detected the reconnection diffusion region. This result is also relevant to other planets with intrinsic magnetosphere. Plain Language Summary Magnetic reconnection is an essential source process in space weather. Reconnection produces many magnetic structures, such as the magnetic flux ropes and reconnection fronts, and ejects them away from the reconnection site. These structures interact with the surrounding space environment during its propagation, which may have great geomagnetic effects. A highly asymmetric earthward propagating magnetic flux rope is often observed in the Earth's magnetotail. It has long been suggested that this asymmetrical magnetic flux rope is formed due to the flux erosion of the earthward part of the flux rope by magnetic reconnection between the flux rope and the geomagnetic field. Despite various theoretical and numerical simulation studies, there has been no observational evidence to confirm this scenario. This paper reports the first observation of magnetic reconnection occurring at the earthward front of a flux rope in the Earth's magnetotail, confirming the previous theoretical predictions and explaining the formation of the asymmetric flux rope which is often observed in the near-Earth magnetotail.
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| 8. |
- Man, H. Y., et al.
(författare)
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Observations of Electron-Only Magnetic Reconnection Associated With Macroscopic Magnetic Flux Ropes
- 2020
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Ingår i: Geophysical Research Letters. - : AMER GEOPHYSICAL UNION. - 0094-8276 .- 1944-8007. ; 47:19
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Tidskriftsartikel (refereegranskat)abstract
- We report a Magnetospheric Multiscale (MMS) mission observation of magnetic reconnection occurring at the edge of a large-scale magnetic flux rope (MFR), the cross-section of which was about 2 R-E. The MFR was observed at the duskside in the Earth's magnetotail and was highly oblique with its axis approximately along theX(GSM)direction. We find an electron-scale current sheet near the edge of this MFR. The Hall magnetic and electric field, super-Alfvenic electron outflow, parallel electric field, and positive energy dissipation were observed associated with the current sheet, which indicates that MMS detected a reconnecting current sheet with a large guide field. Interestingly, ions were not coupled in this reconnection, akin to the electron-only reconnection observed in the turbulent magnetosheath. We further find that the electron-only reconnection is commonly associated with a macroscopic MFR. This result will shed new light on understanding the multiscale coupling associated with an MFR in space plasmas.
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| 9. |
- Zhong, Z. H., et al.
(författare)
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Direct Evidence for Electron Acceleration Within Ion-Scale Flux Rope
- 2020
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Ingår i: Geophysical Research Letters. - : AMER GEOPHYSICAL UNION. - 0094-8276 .- 1944-8007. ; 47:1
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Tidskriftsartikel (refereegranskat)abstract
- Energetic electrons have frequently been observed in small-scale flux ropes. However, whether these energetic electrons were energized directly within the flux rope or not is unknown. In this paper, we present concrete evidence provided by the Magnetospheric Multiscale mission that a secondary flux rope provided strong acceleration for electrons expelled by the reconnection X line. We find that the energetic electron fluxes inside the ion-scale flux rope were larger than those outside the flux rope. Electrons were adiabatically accelerated by betatron and Fermi mechanisms inside the flux rope. The highest energy electrons (>100 keV) were produced by betatron acceleration, whereas Fermi acceleration was unable to accelerate the electrons to high energy probably due to the finite distance of the acceleration region along the field-aligned direction. These results confirm the essential role of ion-scale flux ropes in producing energetic electrons.
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| 10. |
- Zhong, Z. H., et al.
(författare)
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Energy Conversion and Dissipation at Dipolarization Fronts : A Statistical Overview
- 2019
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Ingår i: Geophysical Research Letters. - : AMER GEOPHYSICAL UNION. - 0094-8276 .- 1944-8007. ; 46:22, s. 12693-12701
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Tidskriftsartikel (refereegranskat)abstract
- Dipolarization fronts (DFs) are important for energy conversion, particle acceleration, and flux transport in the magnetotail. The partition of energy conversion between ions and electrons and the energy dissipation at DFs are not well understood. In this paper, we present a statistical study of energy conversion and dissipation of 122 DFs observed by Magnetospheric Multiscale mission in the magnetotail. Statistically, electromagnetic energy transfers to plasma at DF. The released energy is mainly transferred to ions rather than electrons. On average, ions gain energy across the whole DF, while electrons gain energy at the leading part but lose energy at the trailing part of DFs. Joule dissipation J center dot (E+v(e) x B) can be either positive or negative at DFs, and its average value is very small. The kinetic energy dissipation parameter Pi - D does not exhibit clear signatures at the DFs; hence, it is not suitable for quantifying the energy dissipation at DF.
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