scholarly journals Magnetic Topology and Current Sheet Formation

1989 ◽  
Vol 104 (2) ◽  
pp. 277-280
Author(s):  
Spiro K. Antiochos
Keyword(s):  
Magnetic Field ◽  
Current Sheet ◽  
Field Line ◽  
Complex Network ◽  
Rapid Heating ◽  
Negative Polarity ◽  
Coronal Magnetic Field ◽  
Coronal Heating ◽  
Magnetic Topology ◽  
Magnetic Null

AbstractWe describe a mechanism for coronal heating. The basic idea is that since the photospheric flux is observed to consist of a complex pattern of positive and negative polarity regions, the topology of the coronal magnetic field (in particular the connectivity) must be discontinuous over a complex network of surfaces and magnetic null points in the corona. Consequently, photospheric motions of the field line footpoints, even if arbitrarily smooth, result in discontinuous stressing of the field. This produces coronal current sheets, reconnection at the null points, and rapid heating.

Evolution of Large-Scale Coronal Structures

1994 ◽  
Vol 144 ◽  
pp. 29-33
Author(s):  
P. Ambrož
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Large Scale ◽  
Coronal Magnetic Field ◽  
Source Surface ◽  
Solar Cycles ◽  
Characteristic Relationship ◽  
The Magnetic Field ◽  
Coronal Structures

AbstractThe large-scale coronal structures observed during the sporadically visible solar eclipses were compared with the numerically extrapolated field-line structures of coronal magnetic field. A characteristic relationship between the observed structures of coronal plasma and the magnetic field line configurations was determined. The long-term evolution of large scale coronal structures inferred from photospheric magnetic observations in the course of 11- and 22-year solar cycles is described.Some known parameters, such as the source surface radius, or coronal rotation rate are discussed and actually interpreted. A relation between the large-scale photospheric magnetic field evolution and the coronal structure rearrangement is demonstrated.

scholarly journals The current sheet flapping motions induced by non-adiabatic ions: case study

2018 ◽  
Author(s):  
Xinhua Wei ◽  
Chunlin Cai ◽  
Henri Rème ◽  
Iannis Dandouras ◽  
George Parks
Keyword(s):  
Magnetic Field ◽  
Current Sheet ◽  
Field Line ◽  
Magnetic Field Line ◽  
Plasma Sheet ◽  
Plasma Sources ◽  
Shear Structures ◽  
Particle Population ◽  
Alternating Bending

Abstract. In this paper, we analyzed the y-component of magnetic field line curvature in the plasma sheet and found that there are two kinds of shear structures of the flapping current sheet, i.e. symmetric and antisymmetric. The alternating bending orientations of guiding field are exactly corresponding to alternating north-south asymmetries of the bouncing ion population in the sheet center. Those alternating asymmetric plasma sources consequently induce the current sheet flapping motion as a driver. In addition, a substantial particle population with dawnward motion was observed in the center of a bifurcated current sheet. This population is identified as the quasi-adiabatic particles, and provides a net current opposite to the conventional cross-tail current.

Stability of static current sheets connecting plane magnetic null points

1999 ◽  
Vol 61 (4) ◽  
pp. 623-631
Author(s):  
MANUEL NÚÑEZ
Keyword(s):  
Magnetic Field ◽  
Current Sheet ◽  
Lorentz Force ◽  
Critical Points ◽  
Null Point ◽  
The Other ◽  
Magnetic Null ◽  
Local Topology ◽  
The Magnetic Field ◽  
A Current

The configuration created in the plane by the separation of a magnetic hyperbolic null point into two critical points connected by a current sheet is considered. The main parameters are the orders of the zeros of these new null points, which determine the local topology of the magnetic field. It is shown that when the magnetic field is static, the fluid tends to flow orthogonally to the field in the vicinity of the sheet endpoints. Moreover, the Lorentz force pushes one of them towards the other, so the configuration tends to collapse again into a single null point except when the order of both is precisely ½.

scholarly journals Study of magnetic field topology of active region 12192 using an extrapolated non-force-free magnetic field

2018 ◽  
Vol 13 (S340) ◽  
pp. 81-82
Author(s):  
A. Prasad ◽  
R. Bhattacharyya ◽  
Q. Hu ◽  
S. S. Nayak ◽  
Sanjay Kumar
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Free Field ◽  
Coronal Magnetic Field ◽  
Solar Photosphere ◽  
Magnetic Field Topology ◽  
Cycle 24 ◽  
Magnetic Null ◽  
The Magnetic Field ◽  
Force Free Field

AbstractThe solar active region (AR) 12192 was one of the most flare productive region of solar cycle 24, which produced many X-class flares; the most energetic being an X3.1 flare on October 24, 2014 at 21:10 UT. Customarily, such events are believed to be triggered by magnetic reconnection in coronal magnetic fields. Here we use the vector magnetograms from solar photosphere, obtained from Heliospheric Magnetic Imager (HMI) to investigate the magnetic field topology prior to the X3.1 event, and ascertain the conditions that might have caused the flare. To infer the coronal magnetic field, a novel non-force-free field (NFFF) extrapolation technique of the photospheric field is used, which suitably mimics the Lorentz forces present in the photospheric plasma. We also highlight the presence of magnetic null points and quasi-separatrix layers (QSLs) in the magnetic field topology, which are preferred sites for magnetic reconnections and discuss the probable reconnection scenarios.

Photospheric Vortices and Coronal Heating

1994 ◽  
Vol 144 ◽  
pp. 478
Author(s):  
J. B. Zirker
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Power Input ◽  
Coronal Heating ◽  
Photospheric Magnetic Field ◽  
Coronal Loops ◽  
Substantial Fraction ◽  
Realistic Simulation ◽  
Autocorrelation Time ◽  
Intergranular Vortices

AbstractWe have used the results of a realistic simulation of convection to estimate the power input to coronal loops from the twisting of photospheric magnetic field in intergranular vortices. In this simulation, the vorticity is large (a mean of 0.03 s–1) nearly everywhere in the intergranular lanes, not merely at the corners of three granules. We found the autocorrelation time of vorticity images to be 45 s, but individual vortices last as long as 144 s. Our estimate suggests that field line twisting could supply a substantial fraction, if not all, of the required power to the quiet corona.

Magnetic field-line reconnection with jets

1986 ◽  
Vol 35 (2) ◽  
pp. 333-350 ◽  
Author(s):  
A. M. Soward ◽  
E. R. Priest
Keyword(s):  
Magnetic Field ◽  
Numerical Simulations ◽  
Current Sheet ◽  
Field Line ◽  
Magnetic Field Line ◽  
Symmetry Axis ◽  
Steady State Solution ◽  
Magnetic Reynolds Number ◽  
External Boundary ◽  
Reconnection Rate

Some recent numerical simulations of driven magnetic field-line reconnection by Biskamp show no evidence of the Petschek mechanism when the reconnection rate or magnetic Reynolds number are large. Instead, an electric current sheet forms on the symmetry axis, across which a magnetic field is annihilated. The sheet terminates at a Y-point. Fluid driven into the current sheet escapes as jets along the separatrices emanating from the Y-point. This paper shows how many of the features such as the jets can be explained by a simple analytical model. Since the numerical simulations are necessarily on a bounded domain, the importance of the external boundary conditions in setting up a steady-state solution is stressed by illustrative examples.

scholarly journals Revisiting the coronal current sheet model: Parameter range analysis and comparison with the potential field model

2019 ◽  
Vol 631 ◽  
pp. A17 ◽  
Author(s):  
Jennimari Koskela ◽  
Ilpo Virtanen ◽  
Kalevi Mursula
Keyword(s):  
Magnetic Field ◽  
Current Sheet ◽  
Potential Field ◽  
Neutral Line ◽  
Coronal Magnetic Field ◽  
Solar Observatory ◽  
Latitudinal Variation ◽  
Source Surface ◽  
Current Parameter ◽  
Cusp Surface

Aims. We study the properties of the coronal magnetic field according to the current sheet source surface (CSSS) model in 1976–2017 for all physically reasonable values of the three model parameters (cusp surface radius Rcs, source surface radius Rss, and current parameter a), and compare the CSSS field with the potential field source surface (PFSS) model field. Methods. We used the synoptic maps of the photospheric magnetic field from the Wilcox Solar Observatory (WSO), National Solar Observatory/Kitt Peak (NSO/KP), and the NSO Synoptic Optical Long-term Investigations of the Sun Vector Spectromagnetograph (SOLIS/VSM) in order to calculate the coronal magnetic field according to the CSSS and PFSS models. We calculated the coronal field strength, its latitudinal variation and neutral line location, as well as its polarity match with the heliospheric magnetic field. Results. The CSSS model can correct the erroneous latitudinal variation of the PFSS model if the source surface is sufficiently far out with respect to the cusp surface (Rss ≥ 3 ⋅ Rcs). The topology of the neutral line only slightly depends on source surface radius or current parameter, but excludes very low values of the cusp surface (Rcs ≤ 1.5). A comparison of the polarities gives an optimum cusp surface radius that varies in time between 2 and 5; a stronger current yields a larger optimum Rcs. Interestingly, the optimum polarity match percentages and optimum radii vary very similarly in the two models over the four solar cycles we studied. Conclusions. The CSSS model can produce a stronger total coronal flux than the PFSS model and correct its latitudinal variation. However, the topology of the CSSS model is rather independent of horizontal currents and remains very similar to that of the PFSS model. Therefore, the CSSS model cannot improve the match of field polarities between corona and heliosphere.

A search for north-south asymmetry of interplanetary magnetic field and solar plasma

1994 ◽  
Vol 12 (4) ◽  
pp. 279-285 ◽  
Author(s):  
I. Sabbah
Keyword(s):  
Magnetic Field ◽  
Solar Activity ◽  
Solar Cycle ◽  
Interplanetary Magnetic Field ◽  
Current Sheet ◽  
Activity Cycle ◽  
Solar Activity Cycle ◽  
Negative Polarity ◽  
Solar Plasma ◽  
Spiral Angle

Abstract. An analysis of interplanetary magnetic field (IMF) and plasma data taken near 1 AU during solar activity cycle 21 reveals the following. 1. The yearly averaged spiral angle shows a solar cycle dependence. 2. The spiral angle north of the current sheet is 2.4° higher than south of it during both epochs of positive and negative polarities. 3. The included angle is 4.8° higher during the epoch of positive polarity than during the epoch of negative polarity. 4. The asymmetries in the number of away and toward IMF days are correlated with the asymmetries in solar activity. 5. The solar plasma north of the current sheet is hotter, faster and less dense than south of it during the epoch of negative polarity. 6. An asymmetry in the averaged filed magnitude is absent for solar cycle 21.

Magnetic field-line reconnexion by localized enhancement of resistivity. Part 4. Dependence on the magnitude of resistivity

1979 ◽  
Vol 22 (1) ◽  
pp. 1-14 ◽  
Author(s):  
Masayuki Ugai ◽  
Takao Tsuda
Keyword(s):  
Magnetic Field ◽  
Reynolds Number ◽  
Current Sheet ◽  
Field Line ◽  
Magnetic Field Line ◽  
Theoretical Work ◽  
Magnetic Reynolds Number ◽  
Diffusion Region ◽  
Anomalous Resistivity ◽  
Set Up

The present paper quantitatively examines how the process of fast reconnexion depends on the magnitude of the local resistivity enhanced in the vicinity of the magnetic neutral point. It is shown that quasi-steady Petschek-type configurations are set up, one for each of the variously imposed local resistivity enhancements. The fundamental structure of the quasi-steady configuration is largely controlled by the initially indented value of locally enhanced resistivity. It is especially remarked that the width of the diffusion region becomes smaller as the locally enhanced resistivity becomes smaller. We find that each of the quasi-steady configurations presents nothing other than the Petschek-type configuration that corresponds to the allowable maximum reconnexion rate for the relevant magnetic Reynolds number. We also see that the magnitude of fast reconnexion rate has a weak dependence on the local resistivity in the diffusion region. All our numerical results are very consistent with previous theoretical work on the fast reconnexion problem, once the problem is reconsidered from another angle. We hence suggest that the process of fast reconnexion should be viewed as a gross instability, inherent to the current sheet system itself, that can be triggered by some local onset of anomalous resistivity.

scholarly journals Coronal Arcades in the Sun and Their Hydromagnetic Stability

1985 ◽  
Vol 107 ◽  
pp. 483-486
Author(s):  
A. Ray
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Magnetic Field Line ◽  
Basic Mechanism ◽  
Coronal Magnetic Field ◽  
Equilibrium Structure ◽  
The Sun ◽  
Stability And Instability ◽  
Line Tying ◽  
The Stability

Two ribbon flares on the sun are sometimes preceded by luminous arcade like structures in the corona with fillament activity. The arcades which are associated with the coronal magnetic field are sometimes without these fillaments when they are found to be relatively long lived. The reasons underlying the stability and instability of these structures may be relevant in understanding the basic mechanism of two ribbon flares. Here we present results on the equilibrium structure of coronal arcades and their hydromagnetic stability taking into account the effects of magnetic field line-tying on the photosphere.

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