Formation of solar coronal loops through magnetic reconnection in an emerging active region

2021 ◽  
Author(s):  
Zhenyong Hou ◽  
Hui Tian ◽  
Hechao Chen ◽  
Xiaoshuai Zhu ◽  
Jiansen He ◽  
...  
Keyword(s):  
Magnetic Reconnection ◽  
Current Sheet ◽  
Emission Measure ◽  
Three Dimensional ◽  
Transverse Field ◽  
Power Spectral Analysis ◽  
Active Regions ◽  
Building Blocks ◽  
Coronal Loops ◽  
Field Lines

<p>Coronal loops are building blocks of solar active regions (ARs). However, their formation is not well understood. Here we present direct observational evidence for the formation of coronal loops through magnetic reconnection as new magnetic fluxes emerge to the solar atmosphere. Observations in the EUV passbands of SDO/AIA clearly show the newly formed loops following magnetic reconnection within a vertical current sheet. Formation of the loops is also seen in the Hα images taken by NVST. The SDO/HMI observations show that a positive-polarity flux concentration moves toward a negative-polarity one with a speed of ~0.5 km s<sup>-1</sup> before the apparent formation of coronal loops. During the formation of coronal loops, we found signatures of flux cancellation and subsequent enhancement of the transverse field between the two polarities. We have reconstructed the three-dimensional magnetic field structure through a magnetohydrostatic model, which shows field lines consistent with the loops in AIA images. Numerous bright blobs with a width of ~1.5 Mm appear intermittently in the current sheet and move upward with apparent velocities of ~80 km s<sup>-1</sup>. We have also identified plasma blobs moving to the footpoints of the newly formed large loops, with apparent velocities ranging from 30 to 50 km s<sup>-1</sup>. A differential emission measure analysis shows that the temperature, emission measure and density of the bright blobs are 2.5-3.5 MK, 1.1-2.3×10<sup>28</sup> cm<sup>-5</sup> and 8.9-12.9×10<sup>9</sup> cm<sup>-3</sup>, respectively. Power spectral analysis of these blobs indicates that the magnetic reconnection is inconsistent with the turbulent reconnection scenario.</p>

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.

scholarly journals Formation of coronal rain triggered by impulsive heating associated with magnetic reconnection

2019 ◽  
Vol 630 ◽  
pp. A123 ◽  
Author(s):  
P. Kohutova ◽  
E. Verwichte ◽  
C. Froment
Keyword(s):  
Magnetic Reconnection ◽  
Thermal Instability ◽  
Flux Rope ◽  
Coronal Loops ◽  
Rain Event ◽  
Subsequent Formation ◽  
Standard Models ◽  
Field Lines ◽  
Impulsive Heating ◽  
Coronal Rain

Context. Coronal rain consists of cool plasma condensations formed in coronal loops as a result of thermal instability. The standard models of coronal rain formation assume that the heating is quasi-steady and localised at the coronal loop footpoints. Aims. We present an observation of magnetic reconnection in the corona and the associated impulsive heating triggering formation of coronal rain condensations. Methods. We analyse combined SDO/AIA and IRIS observations of a coronal rain event following a reconnection between threads of a low-lying prominence flux rope and surrounding coronal field lines. Results. The reconnection of the twisted flux rope and open field lines leads to a release of magnetic twist. Evolution of the emission of one of the coronal loops involved in the reconnection process in different AIA bandpasses suggests that the loop becomes thermally unstable and is subject to the formation of coronal rain condensations following the reconnection and that the associated heating is localised in the upper part of the loop leg. Conclusions. In addition to the standard models of thermally unstable coronal loops with heating localised exclusively in the footpoints, thermal instability and subsequent formation of condensations can be triggered by the impulsive heating associated with magnetic reconnection occurring anywhere along a magnetic field line.

scholarly journals 3-D numerical simulations of coronal loops oscillations

2009 ◽  
Vol 27 (10) ◽  
pp. 3899-3908 ◽  
Author(s):  
M. Selwa ◽  
L. Ofman
Keyword(s):  
Active Regions ◽  
External Source ◽  
Coronal Loops ◽  
Velocity Perturbation ◽  
Impulsive Excitation ◽  
Kink Mode ◽  
Parametric Studies ◽  
Field Lines ◽  
Significant Distance

Abstract. We present numerical results of 3-D MHD model of a dipole active region field containing a loop with a higher density than its surroundings. We study different ways of excitation of vertical kink oscillations by velocity perturbation: as an initial condition, and as an impulsive excitation with a pulse of a given position, duration, and amplitude. These properties are varied in the parametric studies. We find that the amplitude of vertical kink oscillations is significantly amplified in comparison to horizontal kink oscillations for exciters located centrally (symmetrically) below the loop, but not if the exciter is located a significant distance to the side of the loop. This explains why the pure vertical kink mode is so rarely observed in comparison to the horizontally polarized one. We discuss the role of curved magnetic field lines and the pulse overlapping at one of the loop's footpoints in 3-D active regions (AR's) on the excitation and the damping of slow standing waves. We find that footpoint excitation becomes more efficient in 3-D curved loops than in 2-D curved arcades and that slow waves can be excited within an interval of time that is comparable to the observed one wave-period due to the combined effect of the pulse inside and outside the loop. Additionally, we study the effect of AR topology on the excitation and trapping of loop oscillations. We find that a perturbation acting directly on a single loop excites oscillations, but results in an increased leakage compared to excitation of oscillations in an AR field by an external source.

scholarly journals Statistical Properties of Magnetic Separators in Model Active Regions

2000 ◽  
Vol 195 ◽  
pp. 443-444
Author(s):  
B. T. Welsch ◽  
D. W. Longcope
Keyword(s):  
Active Region ◽  
Solar Corona ◽  
Magnetic Reconnection ◽  
First Principles ◽  
Magnetic Charge ◽  
Active Regions ◽  
Heating Rates ◽  
X Ray ◽  
Field Lines ◽  
Charge Topology

“Transient brightenings” (or “microflares”) regularly deposit 1027 ergs of energy in the solar corona, and account for perhaps 20% of the active corona's power (Shimizu 1995). We assume these events correspond to episodes of magnetic reconnection along magnetic separators in the solar corona. Using the techniques of magnetic charge topology, we model active region fields as arising from normally distributed collections of “magnetic charges”, point-like sources/sinks of flux (or field lines). Here, we present statistically determined separator (X-ray loop) lengths, derived from first principles. We are in the process of statistical calculations of heating rates due to reconnection events along many separators.

scholarly journals 2D and 3D turbulent magnetic reconnection

2009 ◽  
Vol 5 (H15) ◽  
pp. 434-435
Author(s):  
A. Lazarian ◽  
G. Kowal ◽  
E. Vishniac ◽  
K. Kulpa-Dubel ◽  
K. Otmianowska-Mazur
Keyword(s):  
Magnetic Field ◽  
Magnetic Reconnection ◽  
Large Scale ◽  
Gamma Ray ◽  
Three Dimensional ◽  
Turnover Time ◽  
Turbulent Fluid ◽  
Astrophysical Objects ◽  
Field Lines ◽  
The Magnetic Field

AbstractA magnetic field embedded in a perfectly conducting fluid preserves its topology for all times. Although ionized astrophysical objects, like stars and galactic disks, are almost perfectly conducting, they show indications of changes in topology, magnetic reconnection, on dynamical time scales. Reconnection can be observed directly in the solar corona, but can also be inferred from the existence of large scale dynamo activity inside stellar interiors. Solar flares and gamma ray busts are usually associated with magnetic reconnection. Previous work has concentrated on showing how reconnection can be rapid in plasmas with very small collision rates. Here we present numerical evidence, based on three dimensional simulations, that reconnection in a turbulent fluid occurs at a speed comparable to the rms velocity of the turbulence, regardless of the value of the resistivity. In particular, this is true for turbulent pressures much weaker than the magnetic field pressure so that the magnetic field lines are only slightly bent by the turbulence. These results are consistent with the proposal by Lazarian & Vishniac (1999) that reconnection is controlled by the stochastic diffusion of magnetic field lines, which produces a broad outflow of plasma from the reconnection zone. This work implies that reconnection in a turbulent fluid typically takes place in approximately a single eddy turnover time, with broad implications for dynamo activity and particle acceleration throughout the universe. In contrast, the reconnection in 2D configurations in the presence of turbulence depends on resistivity, i.e. is slow.

scholarly journals Global MHD Simulation of the Weak Southward IMF Condition for Different Time Resolutions

2021 ◽  
Vol 8 ◽  
Author(s):  
Kyung Sun Park
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
Magnetic Reconnection ◽  
Three Dimensional ◽  
Slow Solar Wind ◽  
Polar Cap ◽  
Plasma Properties ◽  
Simulation Results ◽  
Field Lines ◽  
The Impact

We performed high-resolution three-dimensional global MHD simulations to determine the impact of weak southward interplanetary magnetic field (IMF) (Bz = −2 nT) and slow solar wind to the Earth’s magnetosphere and ionosphere. We considered two cases of differing, uniform time resolution with the same grid spacing simulation to find any possible differences in the simulation results. The simulation results show that dayside magnetic reconnection and tail reconnection continuously occur even during the weak and steady southward IMF conditions. A plasmoid is generated on closed plasma sheet field lines. Vortices are formed in the inner side of the magnetopause due to the viscous-like interaction, which is strengthened by dayside magnetic reconnection. We estimated the dayside magnetic reconnection which occurred in relation to the electric field at the magnetopause and confirmed that the enhanced electric field is caused by the reconnection and the twisted structure of the electric field is due to the vortex. The simulation results of the magnetic field and the plasma properties show quasi-periodic variations with a period of 9–11 min between the appearances of vortices. Also the peak values of the cross-polar cap potential are both approximately 50 kV, the occurrence time of dayside reconnections are the same, and the polar cap potential patterns are the same in both cases. Thus, there are no significant differences in outcome between the two cases.

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