The coronal field lines of an evolving bipolar magnetic region

1982 ◽  
Vol 255 ◽  
pp. 316 ◽  
Author(s):  
N. R., Jr. Sheeley
Keyword(s):  
Magnetic Region ◽  
Field Lines ◽  
Coronal Field

scholarly journals Magnetic helicity transported by flux emergence and shuffling motions

2012 ◽  
Vol 8 (S294) ◽  
pp. 319-320
Author(s):  
Y. Zhang ◽  
R. Kitai ◽  
K. Takizawa
Keyword(s):  
Magnetic Helicity ◽  
Doppler Velocity ◽  
Similar Distribution ◽  
Normal Velocity ◽  
Flux Emergence ◽  
Helicity Injection ◽  
Field Lines ◽  
Pass Through ◽  
Helical Magnetic Field ◽  
Coronal Field

AbstractMagnetic helicity can be transported from sub-photosphere into corona by the emergence of helical magnetic field lines and the shuffling motions of foot-points of pre-existing coronal field lines. Active region NOAA 10930 was observed by SP and NFI of SOT on board Hinode when it pass through the solar meridian. Based on these observations, we calculate magnetic helicity flow of both terms, by regarding Doppler velocity as normal velocity. The results are compared with which calculated by method proposed by Zhang et. al. (2012). Our results show that helicity injection maps calculated by both methods have similar distribution and the integration values have the same magnitude.

scholarly journals Energetic Solar Electrons – Whistler Bootstrap, Magnetic Knots and Small-scale Reconnection

2010 ◽  
Vol 6 (S274) ◽  
pp. 178-181
Author(s):  
Ilan Roth
Keyword(s):  
Skin Depth ◽  
General Question ◽  
Small Scale ◽  
Topological Invariants ◽  
Relativistic Electrons ◽  
Left Behind ◽  
Seed Population ◽  
Depth Scale ◽  
Field Lines ◽  
Coronal Field

AbstractThe (near) relativistic electrons, emanating from the solar corona in long-lasting, gradual events, are generally observed at 1 AU as delayed vs the less energetic, type-III beams. The observations are consistent with the delayed electrons being energized along the stretched post-CME coronal field lines, when the tail of an anisotropic seed population, which is injected in conjunction to the observed radioheliograph bursts, interacts with the self-excited whistler waves (bootstrap mechanism). These bursts indicate efficient processes where suprathermal seed electrons are injected as a result of magnetic reconnection at the marginally stable coronal configuration left behind the emerging CME. The dependence of the bootstrap mechanism on the electron injection raises the general question of the MHD description and its deviation over the small electron skin-depth scale. The similarity between MHD and knot theories allows one to characterize any turbulent magnetic configuration through topological invariants, while deviation over electron skin-depth scale, characterized by the generalized vorticity, which is enhanced due to density inhomogeneity, creates the conditions for the potential injection sites.

scholarly journals A model of solar flares

1968 ◽  
Vol 35 ◽  
pp. 471-479 ◽  
Author(s):  
P. A. Sturrock
Keyword(s):  
Magnetic Field ◽  
Solar Flares ◽  
Transverse Dimension ◽  
Growth Time ◽  
Closed Field ◽  
Field Region ◽  
Tearing Mode ◽  
Magnetic Region ◽  
Field Lines ◽  
Photospheric Motion

A model of solar flares is proposed in which the preflare state comprises a bipolar magnetic-field structure associated with a bipolar photospheric magnetic region. At low heights, the magnetic-field lines are closed but, at sufficiently great heights, the lines are drawn out into an open structure comprising a bipolar flux tube containing a ‘neutral sheet’ or ‘sheet pinch’. Such a sheet pinch is probably related to a coronal streamer. The energy stored in the closed-field region is derived from photospheric motion whereas energy stored in the open-field region is derived from the non-thermal energy flux which heats the corona and drives the solar wind.The flare itself is identified with reconnection of magnetic field by the tearing-mode resistive instability. If the thickness of the sheet pinch is determined by resistive diffusion and a growth time of the bipolar region of order 1 day, the transverse dimension will be about 104 cm. The rise time of the tearing-mode instability is then a few seconds, compatible with the characteristic time of Type-III radio bursts. One can understand that the time-scale of the reconnection process is of order 102–103 sec if reconnection proceeds by the Petscheck mechanism, with the modification that resistive diffusion is replaced by the more rapid Bohm diffusion.The evolution of a flare, according to this model, appears to fit a number of the observational characteristics of flares.

scholarly journals The Evolution of a Sheared Potential Magnetic Field in the Solar Corona

1990 ◽  
Vol 142 ◽  
pp. 309-312
Author(s):  
J. T. Karpen ◽  
S. K. Antiochos ◽  
C. R. DeVore
Keyword(s):  
Magnetic Field ◽  
Solar Corona ◽  
Boundary Surface ◽  
Null Point ◽  
Current Sheets ◽  
Field Lines ◽  
Line Tying ◽  
Analytic Models ◽  
Coronal Field ◽  
A Current

Several theoretical studies have proposed that, in response to photospheric foot-point motions, current sheets can be generated in the solar corona without the presence of a null point in the initial potential magnetic field. In these analytic models, current sheets form wherever the coronal field dips down and is parallel to the photosphere. A fundamental assumption in these analyses — commonly referred to as the line-tying assumption — is that all coronal field lines are anchored to a boundary surface representing the top of the dense, gas-pressure-dominated photosphere. In theoretical arguments presented elsewhere (Karpen, Antiochos, and DeVore 1989), however, we show that line-tying is not valid for “dipped” coronal fields, and hence that the conclusions of the line-tied models are incorrect. We contend that current sheets will not form if the photosphere-corona interface is represented by a physically valid model. Here we summarize a numerical investigation of the response of a “dipped” potential magnetic field in a hydrostatic-equilibrium atmosphere to shearing motions of the foot points. Our results show that, in the absence of artificial line-tying conditions, a current sheet indeed does not form at the location of the dip. Rather, the dipped magnetic field rises, causing upflows of photospheric and chromospheric plasma.

scholarly journals Solar prominences

2008 ◽  
Vol 4 (S257) ◽  
pp. 223-232
Author(s):  
Brigitte Schmieder ◽  
Guillaume Aulanier ◽  
Tibor Török
Keyword(s):  
Flux Rope ◽  
Transverse Magnetic ◽  
Magnetic Structures ◽  
The North ◽  
Solar Prominences ◽  
Filament Channel ◽  
Solar Filaments ◽  
Field Lines ◽  
Coronal Field

AbstractSolar filaments (or prominences) are magnetic structures in the corona. They can be represented by twisted flux ropes in a bipolar magnetic environment. In such models, the dipped field lines of the flux rope carry the filament material and parasitic polarities in the filament channel are responsible for the existence of the lateral feet of prominences.Very simple laws do exist for the chirality of filaments, the so-called “filament chirality rules”: commonly dextral/sinistral filaments corresponding to left- (resp. right) hand magnetic twists are in the North/South hemisphere. Combining these rules with 3D weakly twisted flux tube models, the sign of the magnetic helicity in several filaments were identified. These rules were also applied to the 180° disambiguation of the direction of the photospheric transverse magnetic field around filaments using THEMIS vector magnetograph data (López Ariste et al. 2006). Consequently, an unprecedented evidence of horizontal magnetic support in filament feet has been observed, as predicted by former magnetostatic and recent MHD models.The second part of this review concerns the role of emerging flux in the vicinity of filament channels. It has been suggested that magnetic reconnection between the emerging flux and the pre-existing coronal field can trigger filament eruptions and CMEs. For a particular event, observed with Hinode/XRT, we observe signatures of such a reconnection, but no eruption of the filament. We present a 3D numerical simulation of emerging flux in the vicinity of a flux rope which was performed to reproduce this event and we briefly discuss, based on the simulation results, why the filament did not erupt.

scholarly journals CDS UV Brightenings Explained by Quasi-separatrices and Bald Patches in an S-shape Active Region

2001 ◽  
Vol 203 ◽  
pp. 314-317
Author(s):  
B. Schmieder ◽  
P. Démoulin ◽  
L. Fletcher ◽  
M. C. López Fuentes ◽  
C. H. Mandrini ◽  
...  
Keyword(s):  
Active Region ◽  
Topological Structure ◽  
Large Scale ◽  
Coronal Magnetic Field ◽  
Stored Energy ◽  
Element Abundances ◽  
Hydrostatic Model ◽  
Field Lines ◽  
Coronal Field ◽  
Field Transition

We present multi-instrument observations of AR 8048, made between June 3 and June 5 1997 as part of SoHO JOP033. This active region (AR) has a sigmoid-like global shape and undergoes transient brightenings through which the stored energy is released.Using a magneto-hydrostatic model, we compute coronal magnetic field. The large-scale magnetic lines confirm the sigmoidal characteristics of the AR. The field lines most closely matching the hotter SoHO/CDS loops extend along the quasi-separatrix-Iayers (QSLs) of the coronal field. Transition region (TR) brightenings observed with SoHO/CDS can be associated with both QSL intersections with the photosphere, and places where separatrices corresponding to bald patches (BPs, sites where field lines are tangent to the photosphere) lie at the photospheric plane. There are suggestions that the element abundances measured in the TR may depend on the type of topological structure present. TR brightenings associated with QSLs have coronal abundances, while those associated with BP separatrices have abundances closer to photospheric values.

scholarly journals Structure and Equilibrium of Coronal Magnetic Fields

1990 ◽  
Vol 142 ◽  
pp. 303-308
Author(s):  
A. A. Van Ballegooijen
Keyword(s):  
Velocity Field ◽  
Coronal Loop ◽  
Spatial Scales ◽  
Simplified Model ◽  
Coronal Loops ◽  
Magnetic Structures ◽  
Coronal Magnetic Fields ◽  
Fine Structures ◽  
Field Lines ◽  
Coronal Field

In “closed” magnetic structures (i.e., coronal loops) the random shuffling of magnetic footpoints in the photosphere causes twisting and braiding of field lines in the corona. If the motions are sufficiently slow, the coronal field evolves through a sequence of force-free equilibrium states. Numerical simulations are presented for a simplified model in which the overall curvature of the coronal loop is neglected. It is shown that magnetic fine structures develop on spatial scales significantly smaller than those of the imposed “photospheric” velocity field.

Disconnection of Coronal Field Lines Due to the Emergence of New Photo-Spheric Flux as the Cause of CMES & Interplanetary Shocks

1996 ◽  
Vol 154 ◽  
pp. 123-127
Author(s):  
S. Bravo
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Solar Surface ◽  
Coronal Magnetic Field ◽  
Interplanetary Shock ◽  
Opposite Polarity ◽  
Interplanetary Shocks ◽  
Closed Structure ◽  
Field Lines ◽  
Coronal Field

AbstractA scenario is presented whereby CMEs and interplanetary shocks are consequences of a large scale rearrangement of the coronal magnetic field induced by the disconnection of field lines from the solar surface due to the emergence of flux with opposite polarity. In this scenario the CME is the mass released from the previously closed structure and the interplanetary shock is formed by the injection of faster solar wind from an extended or newly created coronal hole which results from the opening of the field lines. Here CMEs and interplanetary shocks are associated events, but not cause-effect related. Observational and computational evidence supporting this view is provided.

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