scholarly journals A magnetic reconnection model for hot explosions in the cool atmosphere of the Sun

2021 ◽  
Author(s):  
Lei Ni
Keyword(s):  
Magnetic Reconnection ◽  
Current Sheet ◽  
Large Temperature ◽  
Formation Mechanisms ◽  
Line Profiles ◽  
Turbulent Structures ◽  
Plasma Parameters ◽  
Magnetic Diffusivity ◽  
Reconnection Region ◽  
Initial Plasma

<p>UV bursts and Ellerman bombs are transient brightenings observed in the low solar atmospheres of emerging flux regions. Observations have discovered the cospatial and cotemporal EBs and UV bursts, and their formation mechanisms are still not clear. The multi-thermal components with a large temperature span in these events challenge our understanding of magnetic reconnection and heating mechanisms in the low solar atmosphere. We have studied magnetic reconnection between the emerging and background magnetic fields. The initial plasma parameters are based on the C7 atmosphere model. After the current sheet with dense photosphere plasma is emerged to <span tabindex="0" role="presentation" data-mathml='<math xmlns="http://www.w3.org/1998/Math/MathML"><mn>0.5</mn></math>'><span><span><span>0.5</span></span></span></span> Mm above the solar surface, plasmoid instability appears. The plasmoids collide and coalesce with each other, which makes the plasmas with different densities and temperatures mixed up in the turbulent reconnection region. Therefore, the hot plasmas corresponding to the UV emissions and colder plasmas corresponding to the emissions from other wavelenghts can move together and occur at about the same height. In the meantime, the hot turbulent structures basically concentrate above <span tabindex="0" role="presentation" data-mathml='<math xmlns="http://www.w3.org/1998/Math/MathML"><mn>0.4</mn></math>'><span><span><span>0.4</span></span></span></span> Mm, whereas the cool plasmas extend to much lower heights to the bottom of the current sheet. These phenomena are consistent with the observations of Chen et al. 2019, ApJL. The synthesized Si IV line profiles are similar to the observed one in UV bursts, the enhanced wing of the line profiles can extend to about <span tabindex="0" role="presentation" data-mathml='<math xmlns="http://www.w3.org/1998/Math/MathML"><mn>100</mn></math>'><span><span><span>100</span></span></span></span> km s<span tabindex="0" role="presentation" data-mathml='<math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mi></mi><mrow class="MJX-TeXAtom-ORD"><mo>−</mo><mn>1</mn></mrow></msup></math>'><span><span><span><span></span><span><span><span>−</span><span>1</span></span></span></span></span></span></span>. The differences are significant among the numerical results with different resolutions, which indicate that the realistic magnetic diffusivity is crucial to reveal the fine structures and realistic plasmas heating in these reconnection events. Our results also show that the reconnection heating contributed by ambipolar diffusion in the low chromosphere around the temperature minimum region is not efficient.</p>

scholarly journals A solar filament disconnected by magnetic reconnection

2020 ◽  
Vol 633 ◽  
pp. A121
Author(s):  
Zhike Xue ◽  
Xiaoli Yan ◽  
Liheng Yang ◽  
Jincheng Wang ◽  
Qiaoling Li ◽  
...  
Keyword(s):  
Active Region ◽  
Magnetic Reconnection ◽  
Current Sheet ◽  
Lower Atmosphere ◽  
Mean Velocity ◽  
Reconnection Region ◽  
Resolution Observation ◽  
Solar Filament ◽  
Reconnection Site ◽  
The Right

Aims. We aim to study a high-resolution observation of an asymmetric inflow magnetic reconnection between a filament and its surrounding magnetic loops in active region NOAA 12436 on 2015 October 23. Methods. We analyzed the multiband observations of the magnetic reconnection obtained by the New Vacuum Solar Telescope (NVST) and the Solar Dynamic Observatory. We calculated the NVST Hα Dopplergrams to determine the Doppler properties of the magnetic reconnection region and the rotation of a jet. Results. The filament firstly becomes active and then approaches its southwestern surrounding magnetic loops (L1) with a velocity of 9.0 km s−1. During this period, the threads of the filament become loose in the reconnection region and then reconnect with L1 in turn. L1 is pressed backward by the filament with a velocity of 5.5 km s−1, and then the magnetic reconnection occurs between them. A set of newly formed loops are separated from the reconnection site with a mean velocity of 127.3 km s−1. In the middle stage, some threads of the filament return back first with a velocity of 20.1 km s−1, and others return with a velocity of 4.1 km s−1 after about 07:46 UT. Then, L1 also begins to return with a velocity of 3.5 km s−1 at about 07:47 UT. At the same time, magnetic reconnection continues to occur between them until 07:51 UT. During the reconnection, a linear typical current sheet forms with a length of 5.5 Mm and a width of 1.0 Mm, and a lot of hot plasma blobs are observed propagating from the typical current sheet. During the reconnection, the plasma in the reconnection region and the typical current sheet always shows redshifted feature. Furthermore, the material and twist of the filament are injected into the newly longer-formed magnetic loops by the magnetic reconnection, which leads to the formation of a jet, and its rotation. Conclusions. The observational evidence for the asymmetric inflow magnetic reconnection is investigated. We conclude that the magnetic reconnection does occur in this event and results in the disconnection of the filament. The looseness of the filament may be due to the pressure imbalance between the inside and outside of the filament. The redshifted feature in the reconnection site can be explained by the expansion of the right flank of the filament to the lower atmosphere because of the complex magnetic configuration in this active region.

Test particle acceleration in resistive torsional fan magnetic reconnection using laboratory plasma parameters

2021 ◽  
Vol 87 (6) ◽  
Author(s):  
D.L. Chesny ◽  
N.B. Orange ◽  
K.W. Hatfield
Keyword(s):  
Particle Acceleration ◽  
Magnetic Reconnection ◽  
Three Dimensional ◽  
Laboratory Plasma ◽  
Plasma Parameters ◽  
Astrophysical Plasmas ◽  
Magnetic Field Topology ◽  
Reconnection Region ◽  
Fundamental Process ◽  
Technology Applications

Particle acceleration via magnetic reconnection is a fundamental process in astrophysical plasmas. Experimental architectures are able to confirm a wide variety of particle dynamics following the two-dimensional Sweet–Parker model, but are limited in their reproduction of the fan-spine magnetic field topology about three-dimensional (3-D) null points. Specifically, there is not yet an experiment featuring driven 3-D torsional magnetic reconnection. To move in this direction, this paper expands on recent work toward the design of an experimental infrastructure for inducing 3-D torsional fan reconnection by predicting feasible particle acceleration profiles. Solutions to the steady-state, kinematic, resistive magnetohydrodynamic equations are used to numerically calculate particle trajectories from a localized resistivity profile using well-understood laboratory plasma parameters. We confine a thin, 10 eV helium sheath following the snowplough model into the region of this localized resistivity and find that it is accelerated to energies of ${\approx }2$ keV. This sheath is rapidly accelerated and focused along the spine axis propagating a few centimetres from the reconnection region. These dynamics suggest a novel architecture that may hold promise for future experiments studying solar coronal particle acceleration and for technology applications such as spacecraft propulsion.

scholarly journals Forced magnetic reconnection and plasmoid coalescence

2019 ◽  
Vol 623 ◽  
pp. A15 ◽  
Author(s):  
M. A. Potter ◽  
P. K. Browning ◽  
M. Gordovskyy
Keyword(s):  
Magnetic Reconnection ◽  
Current Sheet ◽  
Energy Release ◽  
External Perturbation ◽  
Mhd Equations ◽  
Magnetic Islands ◽  
Initial Current ◽  
Reconnection Region ◽  
Non Linear ◽  
Forced Magnetic Reconnection

Context. Forced magnetic reconnection, a reconnection event triggered by external perturbation, should be ubiquitous in the solar corona. Energy released during such cases can be much greater than that which was introduced by the perturbation. The exact dynamics of magnetic reconnection events are determined by the structure and complexity of the reconnection region: the thickness of reconnecting layers, the field curvature; the presence, shapes and sizes of magnetic islands. It is unclear how the properties of the external perturbation and the initial current sheet affect the reconnection region properties, and thereby the reconnection dynamics and energy release profile. Aims. We investigate the effect of the form of the external perturbation and initial current sheet on the evolution of the reconnection region and the energy release process. Chiefly we explore the non-linear interactions between multiple, simultaneous perturbations, which represent more realistic scenarios. Future work will use these results in test particle simulations to investigate particle acceleration over multiple reconnection events. Methods. Simulations are performed using Lare2d, a 2.5D Lagrangian-remap solver for the visco-resistive MHD equations. The model of forced reconnection is extended to include superpositions of sinusoidal driving disturbances, including localised Gaussian perturbations. A transient perturbation is applied to the boundaries of a region containing a force-free current sheet. The simulation domain is sufficiently wide to allow multiple magnetic islands to form and coalesce. Results. Island coalescence contributes significantly to energy release and involves rapid reconnection. Long wavelength modes in perturbations dominate the evolution, without the presence of which reconnection is either slow, as in the case of short wavelength modes, or the initial current sheet remains stable, as in the case of noise perturbations. Multiple perturbations combine in a highly non-linear manner: reconnection is typically faster than when either disturbance is applied individually, with multiple low-energy events contributing to the same total energy release.

scholarly journals Onset of 2D magnetic reconnection in the solar photosphere, chromosphere, and corona

2018 ◽  
Vol 609 ◽  
pp. A100
Author(s):  
B. Snow ◽  
G. J. J. Botha ◽  
J. A. McLaughlin ◽  
A. Hillier
Keyword(s):  
Electric Field ◽  
Magnetic Reconnection ◽  
Current Sheet ◽  
Ambipolar Diffusion ◽  
Mhd Equations ◽  
Solar Photosphere ◽  
Sharp Rise ◽  
Start Up ◽  
Reconnection Region ◽  
Advection Term

Aims. We aim to investigate the onset of 2D time-dependent magnetic reconnection that is triggered using an external (non-local) velocity driver located away from, and perpendicular to, an equilibrium Harris current sheet. Previous studies have typically utilised an internal trigger to initiate reconnection, for example initial conditions centred on the current sheet. Here, an external driver allows for a more naturalistic trigger as well as the study of the earlier stages of the reconnection start-up process. Methods. Numerical simulations solving the compressible, resistive magnetohydrodynamic (MHD) equations were performed to investigate the reconnection onset within different atmospheric layers of the Sun, namely the corona, chromosphere and photosphere. Results. A reconnecting state is reached for all atmospheric heights considered, with the dominant physics being highly dependent on atmospheric conditions. The coronal case achieves a sharp rise in electric field (indicative of reconnection) for a range of velocity drivers. For the chromosphere, we find a larger velocity amplitude is required to trigger reconnection (compared to the corona). For the photospheric environment, the electric field is highly dependent on the inflow speed; a sharp increase in electric field is obtained only as the velocity entering the reconnection region approaches the Alfvén speed. Additionally, the role of ambipolar diffusion is investigated for the chromospheric case and we find that the ambipolar diffusion alters the structure of the current density in the inflow region. Conclusions. The rate at which flux enters the reconnection region is controlled by the inflow velocity. This determines all aspects of the reconnection start-up process, that is, the early onset of reconnection is dominated by the advection term in Ohm’s law in all atmospheric layers. A lower plasma-β enhances reconnection and creates a large change in the electric field. A high plasma-β hinders the reconnection, yielding a sharp rise in the electric field only when the velocity flowing into the reconnection region approaches the local Alfvén speed.

MMS Observations of FTE-Type Structures with Internal Magnetic Reconnection

2020 ◽  
Author(s):  
Rungployphan Kieokaew ◽  
Benoit Lavraud ◽  
Naïs Fargette
Keyword(s):  
Magnetic Flux ◽  
Magnetic Reconnection ◽  
Current Sheet ◽  
Flux Rope ◽  
Formation Mechanisms ◽  
Transfer Event ◽  
Flux Tubes ◽  
Magnetospheric Multiscale ◽  
Spacecraft Data ◽  
Upstream Solar Wind

<p>A bipolar magnetic variation B<sub>n</sub> with enhanced core and total fields in spacecraft data are recognized as a Flux Transfer Event (FTE) signature, which corresponds to the passage of a magnetic flux rope structure. Recent literature reported Magnetospheric Multiscale (MMS) observations of FTE signatures with magnetic reconnection signatures at the central current sheet. Among reported cases, electron pitch angle distributions (ePAD) in the suprathermal energy range show different features on either side of the reconnecting current sheet, indicating different magnetic connectivities. This structure is interpreted as interlinked/interlaced flux tubes, possibly formed by converging jets toward the central current sheet that in turn enhance magnetic flux pile-up and facilitate reconnection at the current sheet separating the two flux tubes. By surveying similar events using MMS data, we found some FTE-type structures with reconnection signatures at the central current sheet but with homogeneous ePAD of suprathermal electrons across the structures. Thus, these structures are inconsistent with interlinked flux tubes, but rather a regular flux rope. This leads to a question of how reconnection can occur in those single flux ropes, and their relation with interlinked flux tubes. In this work, we investigate properties of these structures and their related upstream solar-wind conditions. Formation mechanisms of such structures and how reconnection can occur will be discussed.</p>

scholarly journals Electron flat-top distributions around the magnetic reconnection region

2008 ◽  
Vol 113 (A1) ◽  
pp. n/a-n/a ◽  
Author(s):  
Y. Asano ◽  
R. Nakamura ◽  
I. Shinohara ◽  
M. Fujimoto ◽  
T. Takada ◽  
...  
Keyword(s):  
Magnetic Reconnection ◽  
Reconnection Region

scholarly journals Observations of Turbulent Magnetic Reconnection within a Solar Current Sheet

2018 ◽  
Vol 866 (1) ◽  
pp. 64 ◽  
Author(s):  
X. Cheng ◽  
Y. Li ◽  
L. F. Wan ◽  
M. D. Ding ◽  
P. F. Chen ◽  
...  
Keyword(s):  
Magnetic Reconnection ◽  
Current Sheet

scholarly journals Numerical study of the reconnection process between magnetic cloud and heliospheric current sheet

2018 ◽  
Vol 619 ◽  
pp. A82
Author(s):  
Man Zhang ◽  
Yu Fen Zhou ◽  
Xue Shang Feng ◽  
Bo Li ◽  
Ming Xiong
Keyword(s):  
Magnetic Reconnection ◽  
Current Sheet ◽  
Dynamic Process ◽  
Large Scale ◽  
Magnetic Cloud ◽  
Numerical Study ◽  
Three Dimensional ◽  
Heliospheric Current Sheet ◽  
Reconnection Process ◽  
Magnetic Filed

In this paper, we have used a three-dimensional numerical magnetohydrodynamics model to study the reconnection process between magnetic cloud and heliospheric current sheet. Within a steady-state heliospheric model that gives a reasonable large-scale structure of the solar wind near solar minimum, we injected a spherical plasmoid to mimic a magnetic cloud. When the magnetic cloud moves to the heliospheric current sheet, the dynamic process causes the current sheet to become gradually thinner and the magnetic reconnection begin. The numerical simulation can reproduce the basic characteristics of the magnetic reconnection, such as the correlated/anticorrelated signatures in V and B passing a reconnection exhaust. Depending on the initial magnetic helicity of the cloud, magnetic reconnection occurs at points along the boundary of the two systems where antiparallel field lines are forced together. We find the magnetic filed and velocity in the MC have a effect on the reconnection rate, and the magnitude of velocity can also effect the beginning time of reconnection. These results are helpful in understanding and identifying the dynamic process occurring between the magnetic cloud and the heliospheric current sheet.

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