scholarly journals Rapid changes of sunspot structure associated with solar eruptions

2010 ◽  
Vol 6 (S273) ◽  
pp. 15-20
Author(s):  
Haimin Wang ◽  
Chang Liu
Keyword(s):  
High Resolution ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Transverse Field ◽  
Line Of Sight ◽  
Polarity Inversion ◽  
Rapid Changes ◽  
Solar Eruptions ◽  
Polarity Inversion Line ◽  
Coronal Field

AbstractIn this paper we summarize the studies of flare-related changes of photospheric magnetic fields. When vector magnetograms are available, we always find an increase of transverse field at the polarity inversion line (PIL). We also discuss 1 minute cadence line-of-sight MDI magnetogram observations, which usually show prominent changes of magnetic flux contained in the flaring δ spot region. The observed limb-ward flux increases while disk-ward flux decreases rapidly and irreversibly after flares. These observations provides evidences, either direct or indirect, for the theory and prediction of Hudson, Fisher & Welsch (2008) that the photospheric magnetic fields would respond to coronal field restructuring and turn to a more horizontal state near the PIL after eruptions. From the white-light observations, we find that at flaring PIL, the structure becomes darker after an eruption, while the peripheral penumbrae decay. Using high-resolution Hinode data, we find evidence that only dark fibrils in the “uncombed” penumbral structure disappear while the bright grains evolve to G-band bright points after flares.

scholarly journals The Association of Flares to Cancelling Magnetic Features on the Sun

1989 ◽  
Vol 104 (1) ◽  
pp. 197-214
Author(s):  
Silvia H. B. Livi ◽  
Sara Martin ◽  
Haimin Wang ◽  
Guoxiang Ai
Keyword(s):  
Magnetic Fields ◽  
Magnetic Flux ◽  
Common Factor ◽  
Solar Observatory ◽  
The Other ◽  
Line Of Sight ◽  
Evolutionary Changes ◽  
Special Cases ◽  
Close Proximity ◽  
Polarity Inversion Line

AbstractPrevious work relating flares to evolutionary changes of photospheric solar magnetic fields are reviewed and reinterpreted in the light of recent observations of cancelling magnetic fields. In line-of-sight magnetograms and H-alpha filtergrams from Big Bear Solar Observatory, we confirm the following 3 associations: (a) the occurrence of many flares in the vicinity of emerging magnetic flux regions (Rust, 1974), but only at locations where cancellation has been observed or inferred; (b) the occurrence of flares at sites where the magnetic flux is increasing on one side of a polarity inversion line and concurrently decreasing on the other (Martres et al, 1968; Ribes, 1969); and (c) the occurrence of flares at sites where cancellation is the only observed change in the magnetograms for at least several hours before a flare (Martin, Livi, and Wang, 1985). Because cancellation (or the localized decrease in the line-of-sight component of magnetic flux) is the only common factor in all of these circumstances, suggest that cancellation is the more general association that includes the other associations as special cases. We propose the hypothesis that cancellation is a necessary, evolutionary precondition for flares. We also confirm the observation of Martin, Livi, and Wang (1985) that the initial parts of flares occur in close proximity to cancellation sites but that during later phases, the flare emission can spread to other parts of the magnetic field that are weak, strong, or not cancelling.

scholarly journals Observations of photospheric magnetic structure below a dark filament using the Hinode Spectro-Polarimeter

2019 ◽  
Vol 71 (2) ◽  
Author(s):  
Takaaki Yokoyama ◽  
Yukio Katsukawa ◽  
Masumi Shimojo
Keyword(s):  
Magnetic Structure ◽  
Flux Rope ◽  
Transverse Field ◽  
Optical Telescope ◽  
Polarity Inversion ◽  
Normal Orientation ◽  
Normal Polarity ◽  
East Limb ◽  
Polarity Inversion Line ◽  
Dark Filament

Abstract The structure of the photospheric vector magnetic field below a dark filament on the Sun is studied using the observations of the Spectro-Polarimeter attached to the Solar Optical Telescope onboard Hinode. Special attention is paid to discriminating between two suggested models, a flux rope or a bent arcade. “Inverse polarity” orientation is possible below the filament in a flux rope, whereas “normal polarity” can appear in both models. We study a filament in the active region NOAA 10930, which appeared on the solar disk during 2006 December. The transverse field perpendicular to the line of sight has a direction almost parallel to the filament spine with a shear angle of 30°, the orientation of which includes the 180° ambiguity. To know whether it is in the normal orientation or in the inverse one, the center-to-limb variation is used for the solution under the assumption that the filament does not drastically change its magnetic structure during the passage. When the filament is near the east limb, we found that the line-of-site magnetic component below the filament is positive, while it is negative near the west limb.This change of sign indicates that the horizontal photospheric field perpendicular to the polarity inversion line beneath the filament has an “inverse-polarity”, which indicates a flux-rope structure of the filament supporting field.

scholarly journals Vector Magnetic Fields at the Base of Filaments and the Filament Environment

1998 ◽  
Vol 167 ◽  
pp. 98-101 ◽  
Author(s):  
Jingxiu Wang ◽  
Wei Li
Keyword(s):  
Magnetic Fields ◽  
Magnetic Structure ◽  
Field Gradient ◽  
Neutral Line ◽  
Transverse Field ◽  
Line Of Sight ◽  
Horizontal Gradient ◽  
Major Fraction ◽  
Flux System ◽  
Magnetic Neutral Line

AbstractBased on an analysis of three active filaments in AR 6891, we find that vector magnetic fields at the base of filaments and the filament environment is characterized by the following: (1) The transverse field is parallel along the magnetic neutral line for most of the filaments. The average transverse field beneath the filaments is more than 400 G. (2) The horizontal gradient of the line-of-sight field crossing the neutral line is, more or less, constant along the major fraction of a filament, but very steep at the two ends. The average gradient is 0.06 G/km. (3) For each of the filaments there is a squeezing magnetic structure which represents an intrusion of a satellite bipole into the main flux system. The neutral line for a squeezing magnetic structure has a large curvature, a strong sheared transverse field of more than 1 KG, and a steep field gradient of approximate 0.3 G/km. (4) The transverse field and field gradient are clearly enhanced before the filament eruption.

scholarly journals Evolution of Stokes V area asymmetry related to a quiet Sun cancellation observed with GRIS/IFU

2020 ◽  
Vol 634 ◽  
pp. A131
Author(s):  
A. J. Kaithakkal ◽  
J. M. Borrero ◽  
C. E. Fischer ◽  
C. Dominguez-Tagle ◽  
M. Collados
Keyword(s):  
Magnetic Flux ◽  
Opposite Polarity ◽  
Disk Center ◽  
Significant Rise ◽  
Polarity Inversion ◽  
Quiet Sun ◽  
Additional Information ◽  
Line Core ◽  
Polarity Inversion Line ◽  
Field Unit

A quiet Sun magnetic flux cancellation event at the disk center was recorded using the Integral Field Unit (IFU) mounted on the GREGOR Infrared Spectrograph (GRIS). The GRIS instrument sampled the event in the photospheric Si I 10827 Å spectral line. The cancellation was preceded by a significant rise in line core intensity and excitation temperature, which is inferred from Stokes inversions under local thermodynamic equilibrium (LTE). The opposite polarity features seem to undergo reconnection above the photosphere. We also found that the border pixels neighboring the polarity inversion line of one of the polarities exhibit a systematic variation of area asymmetry. Area asymmetry peaks right after the line core intensity enhancement and gradually declines thereafter. Analyzing Stokes profiles recorded from either side of the polarity inversion line could therefore potentially provide additional information on the reconnection process related to magnetic flux cancellation. Further analysis without assuming LTE will be required to fully characterize this event.

scholarly journals Where Do Solar Filaments Form?

2013 ◽  
Vol 8 (S300) ◽  
pp. 445-446 ◽  
Author(s):  
Duncan H Mackay ◽  
Victor Gaizauskas ◽  
Anthony R. Yeates
Keyword(s):  
Magnetic Flux ◽  
Large Scale ◽  
Polarity Inversion ◽  
Solar Filaments ◽  
Polarity Inversion Line

AbstractIn the present study, we consider where large, stable solar filaments form relative to underlying magnetic polarities. We find that 92% of all large stable filaments form in magnetic configurations involving the interaction of two or more bipoles. Only 7% form above the Polarity Inversion Line (PIL) of a single bipole. This indicates that a key element in the formation of large-scale stable filaments is the convergence of magnetic flux, resulting in either flux cancellation or coronal reconnection.

scholarly journals Small-Scale Magnetic Features Observed in the Photosphere

1990 ◽  
Vol 138 ◽  
pp. 129-146 ◽  
Author(s):  
Sara F. Martin
Keyword(s):  
Magnetic Fields ◽  
Magnetic Flux ◽  
Active Regions ◽  
Line Of Sight ◽  
Small Scale ◽  
Quiet Sun ◽  
Magnetic Features

Small-scale solar features identifiable on the quiet sun in magnetograms of the line-of-sight component consist of network, intranetwork, ephemeral region magnetic fields, and the elementary bipoles of ephemeral active regions. Network fields are frequently observed to split into smaller fragments and equally often, small fragments are observed to merge or coalesce into larger clumps; this splitting and merging is generally confined to the borders and vertices of the convection cells known as supergranules. Intranetwork magnetic fields originate near the centers of the supergranule convection cells and appear to increase in magnetic flux as they flow in approximate radial patterns towards the boundaries of the cells.

scholarly journals Photospheric vortex flows close to the polarity inversion line of a fully emerged active region

2019 ◽  
Author(s):  
Jean C. Santos ◽  
Cristiano M. Wrasse
Keyword(s):  
Active Region ◽  
Flow Field ◽  
Critical Points ◽  
Jacobian Matrix ◽  
Line Of Sight ◽  
Geometrical Analysis ◽  
Polarity Inversion ◽  
Average Value ◽  
Polarity Inversion Line ◽  
The One

Abstract. We report on the occurrence of vortexes in flow fields obtained from the evolution of the line-of-sight component of the photospheric magnetic field in a region around the polarity inversion line of a fully emerged active region. Based on a local linear approximation for the flow field, we identify the presence of critical points and classify them according to the eigenvalues of the Jacobian matrix of the linear transformation. Vortexes are associated to the presence of a particular kind of critical point, known as Attracting Focus. Using this method we identified twelve vortexes in the analyzed period and detected the occurrence of other types of critical points, which indicate the complexity of the flow field around the PIL. The detected vortexes show a clockwise preferred sense of rotation with approximately 67 % of the cases. A geometrical analysis of the velocity structures produced an average value of D = 1.63 ± 0.05 for the fractal dimension, which is very close to the one obtained for isotropic homogeneous turbulence (D = 5/3). This suggests that the flow around the polarity inversion line is turbulent in nature.

scholarly journals Converging photospheric vortex flows close to the polarity inversion line of a fully emerged active region

2019 ◽  
Vol 37 (4) ◽  
pp. 603-612
Author(s):  
Jean C. Santos ◽  
Cristiano M. Wrasse
Keyword(s):  
Active Region ◽  
Flow Field ◽  
Critical Points ◽  
Jacobian Matrix ◽  
Line Of Sight ◽  
Geometrical Analysis ◽  
Polarity Inversion ◽  
Average Value ◽  
Polarity Inversion Line ◽  
The One

Abstract. We report on the occurrence of vortexes in flow fields obtained from the evolution of the line-of-sight component of the photospheric magnetic field in a region around the polarity inversion line (PIL) of a fully emerged active region. Based on a local linear approximation for the flow field, we identify the presence of critical points and classify them according to the eigenvalues of the Jacobian matrix of the linear transformation. Converging vortexes are associated with the presence of a particular kind of critical point, known as the attracting focus. We identified 12 converging vortexes in the analyzed period and detected the occurrence of other types of critical points, which indicate the complexity of the flow field around the PIL. The detected vortexes show a clockwise preferred sense of rotation with approximately 67 % of the cases. A geometrical analysis of the velocity structures produced an average value of D‾=1.63±0.05 for the fractal dimension, which is very close to the one obtained for isotropic homogeneous turbulence (D=5/3). This suggests that the flow around the PIL is turbulent in nature.

scholarly journals Pre-Eruption Magnetic Configurations in the Active-Region Solar Photosphere

2010 ◽  
Vol 6 (S273) ◽  
pp. 495-498 ◽  
Author(s):  
Manolis K. Georgoulis
Keyword(s):  
Active Region ◽  
Magnetic Flux ◽  
Magnetic Structure ◽  
Preliminary Report ◽  
Magnetic Polarity ◽  
Small Scale ◽  
Solar Photosphere ◽  
Polarity Inversion ◽  
Magnetic Flux Ropes ◽  
Solar Eruptions

AbstractMost solar eruptions occur above strong photospheric magnetic polarity inversion lines (PILs). What overlays a PIL is unknown, however, and this has led to a debate over the existence of sheared magnetic arcades vs. helical magnetic flux ropes. We argue that this debate may be of little meaning: numerous small-scale magnetic reconnections, constantly triggered in the PIL area, can lead to effective transformation of mutual to self magnetic helicity (i.e. twist and writhe) that, ultimately, may force the magnetic structure above PILs to erupt to be relieved from its excess helicity. This is preliminary report of work currently in progress.

scholarly journals Digital Videomagnetograms in Real Time

1971 ◽  
Vol 43 ◽  
pp. 44-50 ◽  
Author(s):  
Thomas J. Janssens ◽  
Neal K. Baker
Keyword(s):  
Magnetic Field ◽  
High Resolution ◽  
Magnetic Fields ◽  
Real Time ◽  
Temporal Resolution ◽  
Optical Filter ◽  
Line Of Sight ◽  
The Sun ◽  
The Magnetic Field

The Aerospace – NASA Videomagnetograph began operation one month ago, two years after components were ordered and construction began. The design grew out of a desire to obtain magnetic fields in real time using an optical filter. The aim was to study and analyze magnetic configurations and changes, quantitatively if possible, with high spatial and temporal resolution and as much sensitivity as possible. This instrument is restricted to the line-of-sight component of the magnetic field and is primarily intended for high resolution studies of selected regions of the sun. The rationale behind our approach is shown in the next section and the design details in the following.

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