Local Correlation Tracking and the Magnetic Induction Equation

Schuck, P. W.

doi:10.1086/497633

Cited by 91 publications

(113 citation statements)

References 28 publications

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“…We apply the LCT method to calculate the velocity of plasma in the solar photosphere by using observed line-of-sight magnetic field components. Although it is known that there are some problems using LCT (Demoulin & Berger 2003;Schuck 2005;Welsh et al 2004), a comparison of results obtained by LCT and other methods did not reveal a change in the main velocity pattern of photospheric plasma motion. For example, Santos et al (2005) compared the horizontal component of the photospheric velocity obtained by using LCT, ILCT and MEF methods and found that the results are similar.…”

Section: Helicitymentioning

confidence: 89%

Magnetic helicity accumulation and tilt angle evolution of newly emerging active regions

Yang

Zhang²,

Büchner

2009

A&A

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Context. It has been known for years that there is a general dominance of negative (positive) helicity of active regions (ARs) in the northern (southern) solar hemisphere. For a better understanding of the role of helicity in the evolution of active regions, it is necessary to know more about the accumulation of helicity during the emergence of active regions. In particular, different conclusions were drawn in the past about the relationship between the accumulated helicity and the writhe of active regions. Aims. We investigate the accumulation of helicity in newly emerging simple bipolar solar active regions. We also investigate the relation between the accumulated helicity and writhe. Methods. We obtain helicity accumulation by applying Fast Fourier Transforms (FFT) and local correlation tracking (LCT) to MDI data. We deduce the writhe of the active regions according to the evolution of the tilt angle between the connecting line of the weighting centers of opposite polarities in the ARs. Results. It is found that the accumulated helicity is proportional to the exponent of magnetic flux (|H| ∝ Φ 1.85 ) in the 58 selected newly emerged simple ARs. 74% of ARs have a negative (positive) helicity when the above defined tilt angle rotates clockwise (counterclockwise). This means that the accumulated helicity and writhe have the same sign for most of the investigated ARs according to the tilt angle evolution of ARs. We also found that 56% (57.6%) of these ARs in the northern (southern) photosphere provide negative (positive) helicity to the corona in the course of the emergence of magnetic flux.

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Section: Helicitymentioning

confidence: 89%

Magnetic helicity accumulation and tilt angle evolution of newly emerging active regions

Yang

Zhang²,

Büchner

2009

A&A

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“…From the sequence of co-aligned MDI magnetograms, we determined the photospheric velocity maps using the differential affine velocity estimator (DAVE) (Schuck 2005). The DAVE method applies an affine velocity profile to a windowed aperture and is consistent with the magnetic induction equation.…”

Section: Discussionmentioning

confidence: 99%

Magnetic helicity balance during a filament eruption that occurred in active region NOAA 9682

Zuccarello

Romano

Zuccarello

et al. 2011

A&A

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Context. Photospheric shear plasma flows in active regions may be responsible for the magnetic helicity injection in the solar corona not only during the energy storage process before a solar eruption, but also during and after the release of the free magnetic energy caused by the eruption. Indeed, after a filament eruption or expansion the magnetic torque imbalance can induce shear flows that can be responsible for yet another injection of magnetic helicity into the corona. Aims. We investigated the magnetic helicity balance in an active region where a confined solar eruption occurred. This was done to verify a possible relationship between the filament expansion and the helicity transport at its footpoints. We aimed to verify if this variation in the helicity transport rate could be interpreted as a consequence of the magnetic torque imbalance caused by the tube expansion, as proposed by Chae et al. (2003, J. Kor. Astron. Soc., 36, 33). Methods. We used 171 Å TRACE data to measure some geometrical parameters of the new magnetic system produced by a filament eruption that occurred on 2001 November 1 in active region NOAA 9682. We used MDI full disk line-of-sight magnetogram data to measure the accumulation of magnetic helicity in the corona before and after the event.Results. From the measured expansion factor in the magnetic arcade, visible at 171 Å during the eruption, we estimated that the resulting torque imbalance at the photosphere ought to lead to the injection of negative helicity following the eruption. We compared this with measurements of the helicity injection using photospheric velocity and magnetogram data. Conclusions. In contradiction to the expectations from the Chae et al. model, the helicity injection after the eruption was positive. We offer the alternative interpretation that the helicity injection resulted from torque of the opposite sign, generated as the filament lost its negative helicity through magnetic reconnection with its surroundings.

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“…To evaluate the horizontal displacements in the photosphere, we have followed the method described by Schuck (2008) by comparing the magnetic field between two magnetograms taken with a time interval of 12 minutes by means of the Differential Affine Velocity Estimator (Schuck 2005(Schuck , 2006, using an apodization window of 11 pixels (5 5) of full width at half maximum.…”

Section: Resultsmentioning

confidence: 99%

A MULTI-INSTRUMENT ANALYSIS OF a C4.1 FLARE OCCURRING IN a Δ SUNSPOT

Guglielmino¹,

Zuccarello²,

Romano

et al. 2016

ApJ

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We present an analysis of multi-instrument space-and ground-based observations relevant to a C4.1 solar flare that occurred in the active region (AR) NOAA 11267 on 2011 August 6. Solar Dynamics Observatoryobservations indicate that at the flare's beginning, it was localized in the preceding sunspot of the AR, which exhibits a δ configuration. Along the polarity inversion line between its opposite polarities we find a large shear angle of about 80°. The helicity accumulation shows that the AR does not obey the general hemispheric helicity rule. At the flare peak, unique observations taken with the X-Ray Telescope aboard Hinode reveal that the bulk of the X-ray emission takes place in the δ-spot region, where the plasma heats up to 1.9 10 7 · » K. During the gradual phase, we observe the development of a Y-shaped structure in the corona and in the high chromosphere. An extruding structure forms, being directed from the emitting region above the δ spot toward the following sunspot. This structure cools down in a few tens of minutes while moving eastward along a direction opposite to the flare ribbon expansion. Finally, remote brightenings are found at the easternmost footpoint of this structure, appearing as a third flare ribbon in the chromosphere. After some minutes, RHESSI measurements show that the X-ray emission is localized in the region close to the crossing point of the coronal Y-shaped structure. Simultaneously, highresolution (0 15) observations performed at the Swedish 1 m Solar Telescope indicate a decreasing trend of the Ca II H intensity in the flare ribbons with some transient enhancements. All these findings suggest that this event is a manifestation of magnetic reconnection, likely induced by an asymmetric magnetic configuration in a highly sheared region.

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Local Correlation Tracking and the Magnetic Induction Equation

Cited by 91 publications

References 28 publications

Magnetic helicity accumulation and tilt angle evolution of newly emerging active regions

Magnetic helicity accumulation and tilt angle evolution of newly emerging active regions

Magnetic helicity balance during a filament eruption that occurred in active region NOAA 9682

A MULTI-INSTRUMENT ANALYSIS OF a C4.1 FLARE OCCURRING IN a Δ SUNSPOT

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