Fine structure and dynamics in a light bridge inside a solar pore

Hirzberger, J.; Bonet, J. A.; Sobotka, M.; Vázquez, M.; Hanslmeier, A.

doi:10.1051/0004-6361:20011685

Cited by 46 publications

(45 citation statements)

References 29 publications

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“…We also observed an outflow from the light bridge into the umbra. The latter result has already been reported by Hirzberger et al (2002). These authors tracked individual granules in the light bridge by eye to determine their proper motions.…”

Section: Horizontal Velocities Outside and Inside The Poresupporting

confidence: 72%

“…In this paper, we use local correlation tracking techniques (hereafter LCT) applied to segmented binarized images, as described in Roudier et al (1999), to study the behaviour of the flows inside and outside a solar pore with high spatial and temporal resolution and to extend the previous analyses published by Sobotka et al (1999) and Hirzberger et al (2002). The unusually large size of this pore and the good quality and duration of the time sequence of images (73 min) make it appropriate for our purpose.…”

Section: Introductionmentioning

confidence: 99%

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Properties of horizontal flows inside and outside a solar pore

Roudier

Bonet

Sobotka

2002

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Abstract. Horizontal velocities and their temporal variations inside a large pore and in the surrounding granulation are studied from a 73 min sequence of white light frames, acquired at the Swedish Vacuum Solar Telescope (La Palma). The local correlation tracking technique with high spatial (0. 31) and temporal (5 min) resolution was applied to binarized images, yielding 14 independent velocity maps. A ring of divergence centres around the pore was observed in all the maps. Motions directed into the pore, deposited by the divergence centres, continue also within the pore but with magnitudes smaller by factor of 2-3. A link between the variations of large velocity amplitudes around the pore and the brightness fluctuations of umbral dots is suggested. A phase delay between velocity and intensity changes at the periphery of the pore, probably related to the penetration of bright features inwards across the pore's border, was observed.

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Section: Horizontal Velocities Outside and Inside The Poresupporting

confidence: 72%

Section: Introductionmentioning

confidence: 99%

Properties of horizontal flows inside and outside a solar pore

Roudier

Bonet

Sobotka

2002

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“…The three of them on the right side seem to make up one granule. In fact, this granule increases in brightness within the next five minutes and all of the five filaments that are visible at 08:32 UT disappear (see also, Hirzberger et al 2002). But on the image at 09:33 UT, bright elongated points, resembling penumbral grains, become visible at the outskirts of the spot around 11:30 o'clock.…”

Section: Morphology and Evolution Of Light Bridgesmentioning

confidence: 89%

The formation of a sunspot penumbra

Schlichenmaier

Rezaei

González

et al. 2010

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Context. The formation of a penumbra is crucial for our understanding of solar magnetism, but it has not been observed in detail. Aims. We aim to enhance our knowledge of how a sunspot penumbra forms and how sunspots grow in size.Methods. We present a data set of the active region NOAA 11024 acquired at the German VTT with speckle-reconstructed images in the G-band and Ca ii K. The data set includes spectropolarimetric profiles from GFPI in Fe i 617.3 nm and TIP in Fe i 1089.6 nm.Results. On 2009 July 4, at 08:30 UT, a leading spot without penumbra and pores of opposite polarity were present in the active region. For the next 4:40 h, we observed the formation of a penumbra in the leading spot at a cadence of 5 images per second. We produced speckle reconstructed images of 0. 3 spatial resolution or better, interrupted by one large gap of 35 min and a few more small gaps of about 10 min. The leading spot initially has a size of 230 arcsec 2 with only a few penumbral filaments and then grows to a size of 360 arcsec 2 . The penumbra forms in segments, and it takes about 4 h until it encircles half of the umbra, on the side opposite the following polarity. On the side towards the following polarity, elongated granules mark a region of magnetic flux emergence. Conclusions. This ongoing emergence appears to prevent a steady penumbra from forming on this side. While the penumbra forms, the umbral area is constant; i.e., the increase in the total spot area is caused exclusively by the growth of the penumbra. From this we conclude that the umbra has reached an upper size limit and that any new magnetic flux that joins the spot is linked to the process of penumbral formation.

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“…Further measurements of proper motions of bright structures in LBs in a pore were performed by Hirzberger et al (2002). They found irregular motions of grains with velocities of up to 1.5 km s −1 .…”

Section: Introductionmentioning

confidence: 99%

Shear and vortex motions in a forming sunspot

González

Kneer²,

Schlichenmaier

2012

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Aims. We measure proper motions of fine structures in a forming sunspot to infer information about the dynamics of flux emergence at the sub-photospheric level. Methods. The active region NOAA 11024 was observed with the Vacuum Tower Telescope at Observatorio del Teide/Tenerife over several days in July 2009. Here, we concentrate on a two-hour sequence taken on July 4, when the leading spot was at an early stage of its evolution. Speckle reconstructions from Ca ii K images and polarimetric data in Fe i λ6173 allow us to study proper motions of umbral fine structures. Results. We detect three prominent features: (1) A light bridge, divided by a dark lane along its axis, shows proper motions in opposing directions on its sides, with velocities of ∼100-500 m s −1 . The flows are seen in both the Ca ii K and the broadband time sequences. (2) Umbral dots in one umbral region outline a vortex with speeds of up to 550 m s −1 . The direction of the motion of the umbral dots is different from that in the light bridge. (3) At one rim of the umbra, the fine structure of the magnetic field moves horizontally with typical velocities of 250-300 m s −1 , prior to the formation of the penumbra. Conclusions. We report on shear and vortex motions in a forming sunspot and interpret them as tracers of twist relaxation in magnetic flux ropes. We suggest that the forming sunspot contains detached magnetic flux ropes that emerge at the surface with different amounts of twist. As they merge to form a sunspot, they untwist giving rise to the observed shear and vortex motions.

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Fine structure and dynamics in a light bridge inside a solar pore

Cited by 46 publications

References 29 publications

Properties of horizontal flows inside and outside a solar pore

Properties of horizontal flows inside and outside a solar pore

The formation of a sunspot penumbra

Shear and vortex motions in a forming sunspot

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