scholarly journals Electron-scale dynamics of the diffusion region during symmetric magnetic reconnection in space

Science ◽  
2018 ◽  
Vol 362 (6421) ◽  
pp. 1391-1395 ◽  
Author(s):  
R. B. Torbert ◽  
J. L. Burch ◽  
T. D. Phan ◽  
M. Hesse ◽  
M. R. Argall ◽  
...  
Keyword(s):  
Magnetic Reconnection ◽  
Diffusion Region ◽  
Magnetospheric Multiscale ◽  
Energy Conversion Process ◽  
Spatial Dimensions ◽  
Reconnection Site ◽  
Plasma Measurements ◽  
Inflow Conditions ◽  
Fast Reconnection

Magnetic reconnection is an energy conversion process that occurs in many astrophysical contexts including Earth’s magnetosphere, where the process can be investigated in situ by spacecraft. On 11 July 2017, the four Magnetospheric Multiscale spacecraft encountered a reconnection site in Earth’s magnetotail, where reconnection involves symmetric inflow conditions. The electron-scale plasma measurements revealed (i) super-Alfvénic electron jets reaching 15,000 kilometers per second; (ii) electron meandering motion and acceleration by the electric field, producing multiple crescent-shaped structures in the velocity distributions; and (iii) the spatial dimensions of the electron diffusion region with an aspect ratio of 0.1 to 0.2, consistent with fast reconnection. The well-structured multiple layers of electron populations indicate that the dominant electron dynamics are mostly laminar, despite the presence of turbulence near the reconnection site.

MMS observations of electron firehose fluctuations in the magnetic reconnection outflow

2021 ◽  
Author(s):  
Giulia Cozzani ◽  
Yuri Khotyaintsev ◽  
Daniel Graham ◽  
Mats André
Keyword(s):  
Energy Conversion ◽  
Electron Temperature ◽  
Magnetic Reconnection ◽  
Diffusion Region ◽  
Temperature Anisotropy ◽  
Plasma Dynamics ◽  
Background Magnetic Field ◽  
Outflow Region ◽  
Reconnection Site

<p>Plasma waves and instabilities driven by temperature anisotropies are known to play a significant role in plasma dynamics, scattering the particles and affecting particle heating and energy conversion between the electromagnetic fields and the particles. Among these instabilities, the electron firehose instability is driven by electron temperature anisotropy T<sub>e,</sub> > T<sub>e,perp</sub> (with respect to the background magnetic field) and produce nonpropagating oblique modes. </p><p>Magnetic reconnection is characterized by regions of enhanced temperature anisotropy that could drive instabilities - including the electron firehose instability - affecting the particle dynamics and the energy conversion of the process. Yet, the electron firehose instability and its role in the reconnection process is still rather unexplored, especially with in situ measurements. </p><p>We report MMS observations of electron firehose fluctuations observed in the exhaust region of a reconnection site in the magnetotail. The fluctuations are observed in the Earthward outflow relatively close (less than 2 d<sub>i</sub> distance) to the electron diffusion region (EDR). While the characteristics of the fluctuations are compatible with oblique electron firehose fluctuations, the associated firehose instability threshold is not exceeded in the interval where the fluctuations are observed. However, the threshold is exceeded in the EDR. The wave analysis in the EDR suggests that the firehose instability could be active at the reconnection site. We suggest that the firehose fluctuations observed in the outflow region may have been originated at the EDR, where the electron temperature anisotropy exceeds the threshold values, and then advected in the outflow region.</p>

scholarly journals Spatial dimensions of the electron diffusion region in anti-parallel magnetic reconnection

2016 ◽  
Vol 34 (3) ◽  
pp. 357-367 ◽  
Author(s):  
Takuma Nakamura ◽  
Rumi Nakamura ◽  
Hiroshi Haseagwa
Keyword(s):  
Electric Field ◽  
Magnetic Reconnection ◽  
Real Space ◽  
Diffusion Region ◽  
Electron Mass ◽  
Plasma Parameters ◽  
Electron Diffusion ◽  
Background Density ◽  
Spatial Dimensions ◽  
Inner Region

Abstract. Spatial dimensions of the detailed structures of the electron diffusion region in anti-parallel magnetic reconnection were analyzed based on two-dimensional fully kinetic particle-in-cell simulations. The electron diffusion region in this study is defined as the region where the positive reconnection electric field is sustained by the electron inertial and non-gyrotropic pressure components. Past kinetic studies demonstrated that the dimensions of the whole electron diffusion region and the inner non-gyrotropic region are scaled by the electron inertial length de and the width of the electron meandering motion, respectively. In this study, we successfully obtained more precise scalings of the dimensions of these two regions than the previous studies by performing simulations with sufficiently small grid spacing (1∕16–1∕8 de) and a sufficient number of particles (800 particles cell−1 on average) under different conditions changing the ion-to-electron mass ratio, the background density and the electron βe (temperature). The obtained scalings are adequately supported by some theories considering spatial variations of field and plasma parameters within the diffusion region. In the reconnection inflow direction, the dimensions of both regions are proportional to de based on the background density. Both dimensions also depend on βe based on the background values, but the dependence in the inner region ( ∼ 0.375th power) is larger than the whole region (0.125th power) reflecting the orbits of meandering and accelerated electrons within the inner region. In the outflow direction, almost only the non-gyrotropic component sustains the positive reconnection electric field. The dimension of this single-scale diffusion region is proportional to the ion-electron hybrid inertial length (dide)1∕2 based on the background density and weakly depends on the background βe with the 0.25th power. These firm scalings allow us to predict observable dimensions in real space which are indeed in reasonable agreement with past in situ spacecraft observations in the Earth's magnetotail and have important implications for future observations with higher resolutions such as the NASA Magnetospheric Multiscale (MMS) mission.

scholarly journals Magnetospheric Multiscale Observations of the Electron Diffusion Region of Large Guide Field Magnetic Reconnection

2016 ◽  
Vol 117 (1) ◽  
Author(s):  
S. Eriksson ◽  
F. D. Wilder ◽  
R. E. Ergun ◽  
S. J. Schwartz ◽  
P. A. Cassak ◽  
...  
Keyword(s):  
Magnetic Reconnection ◽  
Diffusion Region ◽  
Electron Diffusion ◽  
Guide Field ◽  
Magnetospheric Multiscale

scholarly journals First Resolved Observations of the Demagnetized Electron-Diffusion Region of an Astrophysical Magnetic-Reconnection Site

2012 ◽  
Vol 108 (22) ◽  
Author(s):  
J. D. Scudder ◽  
R. D. Holdaway ◽  
W. S. Daughton ◽  
H. Karimabadi ◽  
V. Roytershteyn ◽  
...  
Keyword(s):  
Magnetic Reconnection ◽  
Diffusion Region ◽  
Electron Diffusion ◽  
Reconnection Site

scholarly journals Secondary Magnetic Reconnection at Earth’s Flank Magnetopause

2021 ◽  
Vol 8 ◽  
Author(s):  
B. B. Tang ◽  
W. Y. Li ◽  
C. Wang ◽  
Yu. V. Khotyaintsev ◽  
D. B. Graham ◽  
...  
Keyword(s):  
Solar Wind ◽  
Magnetic Reconnection ◽  
Open Field ◽  
Global Scale ◽  
Diffusion Region ◽  
Magnetic Shear ◽  
Magnetospheric Multiscale ◽  
Field Lines ◽  
Secondary Ion ◽  
Magnetospheric Field

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.

Magnetic Curvature Analysis on Reconnection Related Structures at Earth’s Magnetopause

2020 ◽  
Author(s):  
Yi Qi ◽  
Christopher T. Russell ◽  
Robert J. Strangeway ◽  
Yingdong Jia ◽  
Roy B. Torbert ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Magnetic Reconnection ◽  
Solar Wind Plasma ◽  
Radius Of Curvature ◽  
Plasma Properties ◽  
Magnetospheric Multiscale ◽  
Reconnection Site ◽  
Field Lines ◽  
The Magnetic Field

<p>Magnetic reconnection is a mechanism that allows rapid and explosive energy transfer from the magnetic field to the plasma. The magnetopause is the interface between the shocked solar wind plasma and Earth’s magnetosphere. Reconnection enables the transport of momentum from the solar wind into Earth’s magnetosphere. Because of its importance in this regard, magnetic reconnection has been extensively studied in the past and is the primary goal of the ongoing Magnetospheric Multiscale (MMS) mission. During magnetic reconnection, the originally anti-parallel fields annihilate and reconnect in a thinned current sheet. In the vicinity of a reconnection site, a prominently increased curvature of the magnetic field (and smaller radius of curvature) marks the region where the particles start to deviate from their regular gyro-motion and become available for energy conversion. Before MMS, there were no closely separated multi-spacecraft missions capable of resolving these micro-scale curvature features, nor examining particle dynamics with sufficiently fast cadence.</p><p>In this study, we use measurements from the four MMS spacecraft to determine the curvature of the field lines and the plasma properties near the reconnection site. We use this method to study FTEs (flux ropes) on the magnetopause, and the interaction between co-existing FTEs. Our study not only improves our understanding of magnetic reconnection, but also resolves the relationship between FTEs and structures on the magnetopause.</p>

scholarly journals Electron-only Reconnection in an Ion-scale Current Sheet at the Magnetopause

2021 ◽  
Vol 922 (1) ◽  
pp. 54
Author(s):  
S. Y. Huang ◽  
Q. Y. Xiong ◽  
L. F. Song ◽  
J. Nan ◽  
Z. G. Yuan ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Standard Model ◽  
Magnetic Reconnection ◽  
Current Sheet ◽  
Diffusion Region ◽  
Ion Outflow ◽  
Magnetospheric Multiscale ◽  
The Standard Model ◽  
Field Lines ◽  
Reconnection Model

Abstract In the standard model of magnetic reconnection, both ions and electrons couple to the newly reconnected magnetic field lines and are ejected away from the reconnection diffusion region in the form of bidirectional burst ion/electron jets. Recent observations propose a new model: electron-only magnetic reconnection without ion coupling in an electron-scale current sheet. Based on the data from the Magnetospheric Multiscale (MMS) mission, we observe a long-extension inner electron diffusion region (EDR) at least 40 d i away from the X-line at the Earth’s magnetopause, implying that the extension of EDR is much longer than the prediction of the theory and simulations. This inner EDR is embedded in an ion-scale current sheet (the width of ∼4 d i, d i is ion inertial length). However, such ongoing magnetic reconnection was not accompanied with burst ion outflow, implying the presence of electron-only reconnection in an ion-scale current sheet. Our observations present a new challenge for understanding the model of standard magnetic reconnection and the electron-only reconnection model in an electron-scale current sheet.

scholarly journals In situ evidence of breaking the ion frozen-in condition via the non-gyrotropic pressure effect in magnetic reconnection

2015 ◽  
Vol 33 (9) ◽  
pp. 1147-1153 ◽  
Author(s):  
L. Dai ◽  
C. Wang ◽  
V. Angelopoulos ◽  
K.-H. Glassmeier
Keyword(s):  
Magnetic Reconnection ◽  
Pressure Effect ◽  
Time History ◽  
Momentum Equation ◽  
Pressure Effects ◽  
Fundamental Aspect ◽  
Diffusion Region ◽  
Pressure Tensor ◽  
Dayside Magnetopause

Abstract. For magnetic reconnection to proceed, the frozen-in condition for both ion fluid and electron fluid in a localized diffusion region must be violated by inertial effects, thermal pressure effects, or inter-species collisions. It has been unclear which underlying effects unfreeze ion fluid in the diffusion region. By analyzing in situ THEMIS (Time History of Events and Macroscale Interactions during Substorms) spacecraft measurements at the dayside magnetopause, we present clear evidence that the off-diagonal components of the ion pressure tensor is mainly responsible for breaking the ion frozen-in condition in reconnection. The off-diagonal pressure tensor, which corresponds to a non-gyrotropic pressure effect in this event, is a fluid manifestation of ion demagnetization in the diffusion region. From the perspective of the ion momentum equation, the reported non-gyrotropic ion pressure tensor is a fundamental aspect in specifying the reconnection electric field that controls how quickly reconnection proceeds.

scholarly journals Cluster observation of continuous reconnection at dayside magnetopause in the vicinity of cusp

2005 ◽  
Vol 23 (6) ◽  
pp. 2199-2215 ◽  
Author(s):  
Y. Zheng ◽  
G. Le ◽  
J. A. Slavin ◽  
M. L. Goldstein ◽  
C. Cattell ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Reconnection ◽  
Electric Fields ◽  
Minimum Variance ◽  
Current Layer ◽  
Normal Surface ◽  
Reconnection Process ◽  
Dayside Magnetopause ◽  
Plasma Measurements

Abstract. In this paper, we present a case study of continuous reconnection at the dayside magnetopause observed by the Cluster spacecraft. On 1 April 2003, the four Cluster spacecraft experienced multiple encounters with the Earth's dayside magnetopause under a fairly stable southwestward interplanetary magnetic field (IMF). Accelerated plasma flows, whose magnitude and direction are consistent with the predictions of the reconnection theory (the Walén relation), were observed at and around the magnetopause current layer for a prolonged interval of ~3 h at two types of magnetopause crossings, one with small magnetic shears and the other one with large magnetic shears. Reversals in the Y component of ion bulk flow between the magnetosheath and magnetopause current layer and acceleration of magnetosheath electrons were also observed. Kinetic signatures using electron and ion velocity distributions corroborate the interpretation of continuous magnetic reconnection. This event provides strong in-situ evidence that magnetic reconnection at the dayside magnetopause can be continuous for many hours. However, the reconnection process appeared to be very dynamic rather than steady, despite the steady nature of the IMF. Detailed analysis using multi-spacecraft magnetic field and plasma measurements shows that the dynamics and structure of the magnetopause current layer/boundary can be very complex. For example, highly variable magnetic and electric fields were observed in the magnetopause current layer. Minimum variance analysis shows that the magnetopause normal deviates from the model normal. Surface waves resulting from the reconnection process may be involved in the oscillation of the magnetopause. Keywords. Magnetospheric physics (Magnetopause, cusp and boundary layers; Solar wind-magnetosphere interactions) – Space plasma physics (magnetic reconnection)

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