| 1. |
- Zhou, M., et al.
(författare)
-
Observations of Secondary Magnetic Reconnection in the Turbulent Reconnection Outflow
- 2021
-
Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 48:4
-
Tidskriftsartikel (refereegranskat)abstract
- Magnetic reconnection and turbulence are the two most important energy dissipation processes in plasma. These two processes intertwine with each other and play important roles in their respective dynamic evolution. Here, we present the first evidence that secondary reconnections occur in the turbulent outflow driven by a primary reconnection in the Earth's magnetotail. We have identified 14 secondary reconnections in a large number of current filaments in the turbulent outflow, which persisted for about one and half an hour. Most of these secondary reconnections were electron-only reconnection that has recently been discovered in the magnetosheath. These secondary reconnections entangled the magnetic field lines and dissipated the magnetic energy in the outflow region far away from the primary X line.
|
|
| 2. |
- Alqeeq, S. W., et al.
(författare)
-
Two Classes of Equatorial Magnetotail Dipolarization Fronts Observed by Magnetospheric Multiscale Mission : A Statistical Overview
- 2023
-
Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 128:10
-
Tidskriftsartikel (refereegranskat)abstract
- We carried out a statistical study of equatorial dipolarization fronts (DFs) detected by the Magnetospheric Multiscale mission during the full 2017 Earth's magnetotail season. We found that two DF classes are distinguished: class I (74.4%) corresponds to the standard DF properties and energy dissipation and a new class II (25.6%). This new class includes the six DF discussed in Alqeeq et al. (2022, ) and corresponds to a bump of the magnetic field associated with a minimum in the ion and electron pressures and a reversal of the energy conversion process. The possible origin of this second class is discussed. Both DF classes show that the energy conversion process in the spacecraft frame is driven by the diamagnetic current dominated by the ion pressure gradient. In the fluid frame, it is driven by the electron pressure gradient. In addition, we have shown that the energy conversion processes are not homogeneous at the electron scale mostly due to the variations of the electric fields for both DF classes.
|
|
| 3. |
- Fu, H. S., et al.
(författare)
-
First Measurements of Electrons and Waves inside an Electrostatic Solitary Wave
- 2020
-
Ingår i: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 124:9
-
Tidskriftsartikel (refereegranskat)abstract
- Electrostatic solitary wave (ESW)-a Debye-scale structure in space plasmas-was believed to accelerate electrons. However, such a belief is still unverified in spacecraft observations, because the ESW usually moves fast in spacecraft frame and its interior has never been directly explored. Here, we report the first measurements of an ESW's interior, by the Magnetospheric Multiscale mission located in a magnetotail reconnection jet. We find that this ESW has a parallel scale of 5 lambda(De) (Debye length), a superslow speed (99 km/s) in spacecraft frame, a longtime duration (250 ms), and a potential drop e phi(0)/kT(e) similar to 5%. Inside the ESW, surprisingly, there is no electron acceleration, no clear change of electron distribution functions, but there exist strong electrostatic electron cyclotron waves. Our observations challenge the conventional belief that ESWs are efficient at particle acceleration.
|
|
| 4. |
- Liu, Chunxin, 1991-, et al.
(författare)
-
Cross-scale Dynamics Driven by Plasma Jet Braking in Space
- 2022
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 926:2
-
Tidskriftsartikel (refereegranskat)abstract
- Plasma jets are ubiquitous in space. In geospace, jets can be generated by magnetic reconnection. These reconnection jets, typically at fluid scale, brake in the near-Earth region, dissipate their energies, and drive plasma dynamics at kinetic scales, generating field-aligned currents that are crucial to magnetospheric dynamics. Understanding of the cross-scale dynamics is fundamentally important, but observation of coupling among phenomena at various scales is highly challenging. Here we report, using unprecedentedly high-cadence data from NASA's Magnetospheric Multiscale Mission, the first observation of cross-scale dynamics driven by jet braking in geospace. We find that jet braking causes MHD-scale distortion of magnetic field lines and development of an ion-scale jet front that hosts strong Hall electric fields. Parallel electric fields arising from the ion-scale Hall potential generate intense electron-scale field-aligned currents, which drive strong Debye-scale turbulence. Debye-scale waves conversely limit intensity of the field-aligned currents, thereby coupling back to the large-scale dynamics. Our study can help in understanding how energy deposited in large-scale structures is transferred into small-scale structures in space.
|
|
| 5. |
- Man, H. Y., et al.
(författare)
-
Observations of Electron-Only Magnetic Reconnection Associated With Macroscopic Magnetic Flux Ropes
- 2020
-
Ingår i: Geophysical Research Letters. - : AMER GEOPHYSICAL UNION. - 0094-8276 .- 1944-8007. ; 47:19
-
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.
|
|
| 6. |
- Tang, B-B, et al.
(författare)
-
Electron Mixing and Isotropization in the Exhaust of Asymmetric Magnetic Reconnection With a Guide Field
- 2020
-
Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 47:14
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate an exhaust crossing of asymmetric guide field reconnection observed by Magnetospheric Multiscale (MMS) mission at Earth's dayside magnetopause. One MMS spacecraft (MMS 4) observes multicomponent electron distributions, including two counterstreaming electron beams, while the other three MMS spacecraft, with a separation of similar to 30 km, record nearly isotropic electron distributions. As counterstreaming electrons are unstable for the electron two-stream instability, our observations suggest that the electrostatic waves generated by the fast-growing electron two-stream instability can contribute to the rapid isotropization of electron distributions in the reconnection exhaust, indicating that wave-particle interactions play an important role in electron dynamics.
|
|
| 7. |
- Tang, B. B., et al.
(författare)
-
Secondary Magnetic Reconnection at Earth's Flank Magnetopause
- 2021
-
Ingår i: Frontiers in Astronomy and Space Sciences. - : Frontiers Media SA. - 2296-987X. ; 8
-
Tidskriftsartikel (refereegranskat)abstract
- We report local secondary magnetic reconnection at Earth's flank magnetopause by using the Magnetospheric Multiscale observations. This reconnection is found at the magnetopause boundary with a large magnetic shear between closed magnetospheric field lines and the open field lines generated by the primary magnetopause reconnection at large scales. Evidence of this secondary reconnection are presented, which include a secondary ion jet and the encounter of the electron diffusion region. Thus the observed secondary reconnection indicates a cross-scale process from a global scale to an electron scale. As the aurora brightening is also observed at the morning ionosphere, the present secondary reconnection suggests a new pathway for the entry of the solar wind into geospace, providing an important modification to the classic Dungey cycle.
|
|
| 8. |
- Zhang, L. Q., et al.
(författare)
-
MMS Observation on the Cross-Tail Current Sheet Roll-up at the Dipolarization Front
- 2021
-
Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 126:4
-
Tidskriftsartikel (refereegranskat)abstract
- We perform a case study on the evolution of the current sheet in different regions around the dipolarization front (DF), including magnetic-dip preceding the DF, front at the DF, and magnetic pileup region (MPR) behind the DF based on magnetospheric multiscale (MMS) observation on July 31, 2017. In this event, MMS1 stays inside the current sheet during the whole bursty bulk flow (BBF) interval. Our analysis reveals that the cross-tail current sheet at the DF is rolled up, signified by the depression (-V-z/-B-z) at the dip and elevation (+V-z/+B-z) at the front. The minimum variance analysis on the magnetic field method is applied to obtain the normal direction of the current sheet. The result confirms the roll-up, that is, downward at the depressed current sheet and upward at the elevated current sheet. The current sheet roll-up at the DF is asymmetric, with steeper elevation than depression. The elevation angle of the elevated current sheet is evaluated to be similar to 30 degrees. Strong duskward and predominantly perpendicular J spike (similar to 90 nA/m(2)) concentrate at the interface between the dip and the front. The strength of the current of the J-spike is about nine/three times the current at the dip/front. The front is characterized by positive E center dot J. In the dip/MPR, no such preference is seen. Ion/Electron pitch angle distributions exhibit significant and different evolutions in the roll-up current sheet from dip to front, including their energy-dependence and distributions. Finally, the roll-up current sheet could decelerate BBF and change the flow structure. The potential significance of the roll-up current sheet on BBF evolution is emphasized.
|
|
| 9. |
- Alqeeq, S. W., et al.
(författare)
-
Investigation of the homogeneity of energy conversion processes at dipolarization fronts from MMS measurements
- 2022
-
Ingår i: Physics of Plasmas. - : American Institute of Physics (AIP). - 1070-664X .- 1089-7674. ; 29:1
-
Tidskriftsartikel (refereegranskat)abstract
- We report on six dipolarization fronts (DFs) embedded in fast earthward flows detected by the Magnetospheric Multiscale mission during a substorm event on 23 July 2017. We analyzed Ohm's law for each event and found that ions are mostly decoupled from the magnetic field by Hall fields. However, the electron pressure gradient term is also contributing to the ion decoupling and likely responsible for an electron decoupling at DF. We also analyzed the energy conversion process and found that the energy in the spacecraft frame is transferred from the electromagnetic field to the plasma (J & BULL; E > 0) ahead or at the DF, whereas it is the opposite (J & BULL; E < 0) behind the front. This reversal is mainly due to a local reversal of the cross-tail current indicating a substructure of the DF. In the fluid frame, we found that the energy is mostly transferred from the plasma to the electromagnetic field (J & BULL; E & PRIME; < 0) and should contribute to the deceleration of the fast flow. However, we show that the energy conversion process is not homogeneous at the electron scales due to electric field fluctuations likely related to lower-hybrid drift waves. Our results suggest that the role of DF in the global energy cycle of the magnetosphere still deserves more investigation. In particular, statistical studies on DF are required to be carried out with caution due to these electron scale substructures.
|
|
| 10. |
- Gao, C. -H, et al.
(författare)
-
Effect of the Electric Field on the Agyrotropic Electron Distributions
- 2021
-
Ingår i: Geophysical Research Letters. - : AMER GEOPHYSICAL UNION. - 0094-8276 .- 1944-8007. ; 48:5
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate agyrotropic electron distributions from two magnetopause events observed by magnetospheric multiscale (MMS) spacecraft. Agyrotropic electron distributions can be generated by the finite electron gyration at an electron-scale boundary, and the electric field normal to this boundary usually contributes to the electron acceleration to make the agyrotropic distributions more apparent. The effect of the electric field becomes important only when it is sufficiently strong and local, meaning its electrostatic potential is comparable to or larger than the electron temperature, and its width is smaller than the electron thermal gyroradius, so that this electric field can directly accelerate part of the electrons out of the original core to form agyrotropic electron distributions. Also, we reproduce the measured electron "finger" structures from test particle simulations, which can be effectively suppressed by increasing the sampling rate of the electron measurement. Plain Language Summary Agyrotropic electron distributions reveal valuable information of electron dynamics at electron scales, and the generation of these distributions have been extensively studied. In this study, we provide a new possibility to generate agyrotropic electron distributions with a strong localized electric field, which can accelerate part of electrons out of the original electron core to form agyrotropic distributions. As such large-amplitude small-scale electric field fluctuations are frequently observed in turbulent plasma environments, we suggest that more agyrotropic electron distributions can be observed with high temporal resolution measurements.
|
|
