The velocity structure of moving magnetic feature pairs
around sunspots: support for the U-loop model

Zhang, Jun; Solanki, S. K.; Woch, J.; Wang, Jingxiu

doi:10.1051/0004-6361:20077900

Cited by 23 publications

(15 citation statements)

References 36 publications

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“…Hagenaar & Shine (2005) found that MMFs begin at high velocities of 1.8 km s −1 near the outer boundary of the penumbra, which is faster than average moat velocities. Zhang et al (2007) also found an outward decrease in flow velocity of MMFs from 0.6 km s −1 to 0.35 km s −1 . Sainz Dalda & Martínez Pillet (2005) and Ravindra (2006) found that MMFs originate in the outer penumbra.…”

Section: Introductionmentioning

confidence: 75%

The three-dimensional structure of sunspots

Balthasar¹,

Muglach²

2010

A&A

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Aims. Many sunspots are surrounded by a radial outflow called the moat flow. We investigate the moat flow at two different heights of the solar atmosphere for a sunspot whose magnetic properties were reported in the first paper of this series. Methods. We use two simultaneous time series taken with the Transition Region And Coronal Explorer (TRACE) in white light and in the UV at 170 nm. The field-of-view is centered on the small sunspot NOAA 10886 located near disk center. Horizontal velocities are derived by applying two different local correlation tracking techniques. Results. Outflows are found everywhere in the moat. In the inner moat, the velocities from the UV series are larger than those from white light, whereas in the outer part of the moat we find the converse result. Conclusions. The results imply that the white light velocities represent a general outflow of the quiet sun plasma in the moat, while UV velocities are dominated by small bright points that move faster than the general plasma flow.

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Section: Introductionmentioning

confidence: 75%

The three-dimensional structure of sunspots

Balthasar¹,

Muglach²

2010

A&A

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“…This supports the ''sea serpent'' concept for MMFs, whereby the horizontal penumbral fields undulate into and out of the solar surface ( Harvey & Harvey 1973;Schlichenmaier 2002). Many authors have proposed that the fluctuating penumbral fields and the subsequent MMFs are produced by Evershed flows (e.g., Ryutova et al 1998;Martínez Pillet 2002;Thomas et al 2002;Schlichenmaier 2002;Zhang et al 2003Zhang et al , 2007bCabrera Solana et al 2006). On the other hand, MMFs located on the lines extrapolated from the penumbral spines have magnetic fields that are more vertical than those of their surroundings (Kubo et al 2007a).…”

Section: Introductionmentioning

confidence: 82%

Disintegration of Magnetic Flux in Decaying Sunspots as Observed with theHinodeSOT

Kubo

Lites

Ichimoto

et al. 2008

ApJ

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Continuous observations of sunspot penumbrae with the Solar Optical Telescope aboard Hinode clearly show that the outer boundary of the penumbra fluctuates around its averaged position. The penumbral outer boundary moves inward when granules appear in the outer penumbra. We discover that such granules appear one after another while moving magnetic features (MMFs) are separating from the penumbral ''spines'' (penumbral features that have fields that are stronger and more vertical than those of their surroundings). These granules that appear in the outer penumbra often merge with bright features inside the penumbra that move with the spines as they elongate toward the moat region. This suggests that convective motions around the penumbral outer boundary are related to the disintegration of magnetic flux in the sunspot. We also find that dark penumbral filaments frequently elongate into the moat region in the vicinity of MMFs that detach from penumbral spines. Such elongating dark penumbral filaments correspond to nearly horizontal fields extending from the penumbra. Pairs of MMFs with positive and negative polarities are sometimes observed along the elongating dark penumbral filaments. This strongly supports the notion that such elongating dark penumbral filaments have magnetic fields with a ''sea serpent''-like structure. Evershed flows, which are associated with the penumbral horizontal fields, may be related to the detachment of the MMFs from the penumbral spines, as well as to the formation of the MMFs along the dark penumbral filaments that elongate into the moat region.

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“…Their magnetic configuration must be that of a -loop, since this is the shape of the field lines in the bipolar structures while they still reside in the penumbra. Zhang et al (2007) and Cabrera have deduced a similar configuration for bipolar MMFs. Our interpretation of the observations is summarized in Fig.…”

Section: Discussionmentioning

confidence: 98%

Detection of sea-serpent field lines in sunspot penumbrae

Dalda

Rubio

2008

A&A

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Aims. We investigate the spatial distribution of magnetic polarities in the penumbra of a spot observed very close to disk center. Methods. High angular and temporal resolution magnetograms taken with the Narrowband Filter Imager aboard Hinode are used in this study. They provide continuous and stable measurements in the photospheric Fe i 630.25 line for long periods of time.Results. Our observations show small-scale, elongated, bipolar magnetic structures that appear in the mid penumbra and move radially outward. They occur in between the more vertical fields of the penumbra, and can be associated with the horizontal fields that harbor the Evershed flow. Many of them cross the outer penumbral boundary, becoming moving magnetic features in the sunspot moat. We determine the properties of these structures, including their sizes, proper motions, footpoint separation, and lifetimes. Conclusions. The bipolar patches can be interpreted as being produced by sea-serpent field lines that originate in the mid penumbra and eventually leave the spot in the form moving magnetic features. The existence of such field lines has been inferred from Stokes inversions of spectropolarimetric measurements at lower angular resolution, but this is the first time they are imaged directly. Our observations add another piece of evidence in favor of the uncombed structure of penumbral magnetic fields.

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The velocity structure of moving magnetic feature pairs around sunspots: support for the U-loop model

Cited by 23 publications

References 36 publications

The three-dimensional structure of sunspots

The three-dimensional structure of sunspots

Disintegration of Magnetic Flux in Decaying Sunspots as Observed with theHinodeSOT

Detection of sea-serpent field lines in sunspot penumbrae

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