Shear and vortex motions in a forming sunspot

González, N. Bello; Kneer, F.; Schlichenmaier, R.

doi:10.1051/0004-6361/201118005

Cited by 10 publications

(5 citation statements)

References 28 publications

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“…This seems possible because it would take some two hours to cross the LB if the flow has a speed of 1 km s −1 (Hirzberger et al 2002;Louis et al 2008). Visual inspection of our G-band movie supports the presence of such a flow: Proper motions are seen that could be a signature of shear flows in the LB (Bello González et al 2011).…”

Section: Light Bridges As Channels For Magnetic Fluxsupporting

confidence: 53%

The formation of sunspot penumbra. I. Magnetic field properties

Rezaei,

Gonzalez,

Schlichenmaier

2011

Preprint

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Aims. We study the magnetic flux emergence and formation of a sunspot penumbra in the active region NOAA 11024. Methods. We simultaneously observed the Stokes parameters of the photospheric iron lines at 1089.6 nm with the TIP and 617.3 nm with the GFPI spectropolarimeters along with broad-band images using G-band and Ca ii K filters at the German VTT. The photospheric magnetic field vector was reconstructed from an inversion of the measured Stokes profiles. Using the AZAM code, we converted the inclination from line-of-sight (LOS) to the local reference frame (LRF). Results. Individual filaments are resolved in maps of magnetic parameters. The formation of the penumbra is intimately related to the inclined magnetic field. No penumbra forms in areas with strong magnetic field strength and small inclination. Within 4.5 h observing time, the LRF magnetic flux of the penumbra increases from 9.7 × 10 20 to 18.2 × 10 20 Mx, while the magnetic flux of the umbra remains constant at ∼ 3.8 × 10 20 Mx. Magnetic flux in the immediate surroundings is incorporated into the spot, and new flux is supplied via small flux patches (SFPs), which on average have a flux of 2-3 × 10 18 Mx. The spot's flux increase rate of 4.2 × 10 16 Mx s −1 corresponds to the merging of one SFP per minute. We also find that during the formation of the spot penumbra: a) the maximum magnetic field strength of the umbra does not change, b) the magnetic neutral line keeps the same position relative to the umbra, c) the new flux arrives on the emergence side of the spot while the penumbra forms on the opposite side, d) the average LRF inclination of the light bridges decreases from 50 • to 37 • , and e) as the penumbra develops, the mean magnetic field strength at the spot border decreases from 1.0 to 0.8 kG. Conclusions. The SFPs associated with elongated granules are the building blocks of structure formation in active regions. During the sunspot formation, their contribution is comparable to the coalescence of pores. Besides a set of critical parameters for the magnetic field, a quiet environment in the surroundings is important for penumbral formation. As remnants of trapped granulation between merging pores, the light bridges are found to play a crucial role in the formation process. They seem to channel the magnetic flux through the spot during its formation. Light bridges are also the locations where the first penumbral filaments form.

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Section: Light Bridges As Channels For Magnetic Fluxsupporting

confidence: 53%

The formation of sunspot penumbra. I. Magnetic field properties

Rezaei,

Gonzalez,

Schlichenmaier

2011

Preprint

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“…The southern footpoint of the prominence was lying in close proximity to the active region. Photospheric vortex flows are more frequent near the active region (Bello González et al 2012;Dhara et al 2014) thus it may explain why the southern footpoint had manifested larger twist as compared to the northern footpoint which was anchored at the quiet region of the Sun. However, it should be noted that the photospheric vortex motions cannot be measured because the footpoints of the prominence were at the limb.…”

Section: Discussionmentioning

confidence: 99%

Twisting/Swirling Motions during a Prominence Eruption as Seen from SDO/AIA

Pant

Datta

Banerjee

et al. 2018

ApJ

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A quiescent prominence was observed at north-west limb of the Sun using different channels of Atmospheric Imaging Assembly (AIA) onboard Solar Dynamics Observatory (SDO). We report and analyse twisting/swirling motions during and after the prominence eruption. We segregate the observed rotational motions into small and large scale. Small scale rotational motions manifest in the barbs of the prominence while the large scale rotation manifests as the roll motion during the prominence eruption. We noticed that both footpoints of the prominence rotate in the counter-clockwise direction. We propose that similar sense of rotation in both footpoints leads to prominence eruption. The prominence erupted asymmetrically near the southern footpoint which may be due to uneven mass distribution and location of the cavity near southern footpoint.Furthermore, we study the swirling motion of the plasma along different circular paths in the cavity of the prominence after the prominence eruption. The rotational velocities of the plasma moving along different circular paths are estimated to be ∼ 9-40 km s −1 . These swirling motions can be explained in terms of twisted magnetic field lines in the prominence cavity. Finally, we observe the twist built up in the prominence, being carried away by the coronal mass ejection (CME) as seen in the Large Angle Spectrometric Coronagraph (LASCO) onboard Solar and Heliospheric Observatory (SOHO).

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“…The separation between the parent and fragment, estimated as the distance between their centroid positions, increased almost linearly from approximately 10 to 23 in 5 days. As the rotation of the fragment is more pronounced than its parent, it would suggest that the sunspot as a whole is comprised of several individual magnetic strands rooted to a common flux system rooted deeper in the photosphere (Bello González et al 2012).…”

Section: Rotation Of Fragment About Parent Sunspotmentioning

confidence: 99%

ANALYSIS OF A FRAGMENTING SUNSPOT USINGHINODEOBSERVATIONS

Louis

Ravindra

Mathew

et al. 2012

ApJ

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We employ high resolution filtergrams and polarimetric measurements from Hinode to follow the evolution of a sunspot for eight days starting on June 28, 2007. The imaging data were corrected for intensity gradients, projection effects, and instrumental stray light prior to the analysis. The observations show the formation of a light bridge at one corner of the sunspot by a slow intrusion of neighbouring penumbral filaments. This divided the umbra into two individual umbral cores. During the light bridge formation, there was a steep increase in its intensity from 0.28 to 0.7 I QS in nearly 4 hr, followed by a gradual increase to quiet Sun (QS) values in 13 hr. This increase in intensity was accompanied by a large reduction in the field strength from 1800 G to 300 G. The smaller umbral core gradually broke away from the parent sunspot nearly 2 days after the formation of the light bridge rendering the parent spot without a penumbra at the location of fragmentation. The penumbra in the fragment disappeared first within 34 hr, followed by the fragment whose area decayed exponentially with a time constant of 22 hr. In comparison, the parent sunspot area followed a linear decay rate of 0.94 Mm 2 hr −1 . The depleted penumbra in the parent sunspot regenerated when the inclination of the magnetic field at the penumbra-QS boundary became within 40 • from being completely horizontal and this occurred near the end of the fragment's lifetime. After the disappearance of the fragment, another light bridge formed in the parent which had similar properties as the fragmenting one, but did not divide the sunspot. The significant weakening in field strength in the light bridge along with the presence of granulation is suggestive of strong convection in the sunspot which might have triggered the expulsion and fragmentation of the smaller spot. Although the presence of QS photospheric conditions in sunspot umbrae could be a necessary condition for fragmentation, it is not a sufficient one. ABSTRACTWe employ high resolution filtergrams and polarimetric measurements from Hinode to follow the evolution of a sunspot for eight days starting on June 28, 2007. The imaging data were corrected for intensity gradients, projection effects, and instrumental stray light prior to the analysis. The observations show the formation of a light bridge at one corner of the sunspot by a slow intrusion of neighbouring penumbral filaments. This divided the umbra into two individual umbral cores. During the light bridge formation, there was a steep increase in its intensity from 0.28 to 0.7 I QS in nearly 4 hr, followed by a gradual increase to quiet Sun (QS) values in 13 hr. This increase in intensity was accompanied by a large reduction in the field strength from 1800 G to 300 G. The smaller umbral core gradually broke away from the parent sunspot nearly 2 days after the formation of the light bridge rendering the parent spot without a penumbra at the location of fragmentation. The penumbra in the fragment disappeared first within 34 hr, followed by the f...

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Shear and vortex motions in a forming sunspot

Cited by 10 publications

References 28 publications

The formation of sunspot penumbra. I. Magnetic field properties

The formation of sunspot penumbra. I. Magnetic field properties

Twisting/Swirling Motions during a Prominence Eruption as Seen from SDO/AIA

ANALYSIS OF A FRAGMENTING SUNSPOT USINGHINODEOBSERVATIONS

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