High‐Resolution Proper Motions in a Sunspot Penumbra

Márquez, I.; Alméida, J. Sánchez; Bonet, J. A.

doi:10.1086/498668

Cited by 21 publications

(25 citation statements)

References 49 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…3, we observe apparent motions of penumbral grains toward the umbra both in forming and stable penumbrae. This behaviour is well known for developed penumbrae and the typical amplitude of these motions is around 0.4 km s −1 , which is in agreement with previous studies (Wang & Zirin 1992;Sobotka et al 1999;Márquez et al 2006;Jurčák et al 2014b).…”

Section: The Forming Up Boundary Vs the Stable Up Boundarysupporting

confidence: 92%

A distinct magnetic property of the inner penumbral boundary

Jurčák

González

Schlichenmaier

et al. 2015

A&A

View full text Add to dashboard Cite

Context. A sunspot emanates from a growing pore or protospot. In order to trigger the formation of a penumbra, large inclinations at the outskirts of the protospot are necessary. The penumbra develops and establishes by colonising both umbral areas and granulation. Evidence for a unique stable boundary value for the vertical component of the magnetic field strength, B stable ver , was found along the umbra-penumbra boundary of developed sunspots. Aims. We study the changing value of B ver as the penumbra forms and as it reaches a stable state. We compare this with the corresponding value in fully developed penumbrae. Methods. We use broadband G-band images and spectropolarimetric GFPI/VTT data to study the evolution of and the vertical component of the magnetic field on a forming umbra-penumbra boundary. For comparison with stable sunspots, we also analyse the two maps observed by Hinode/SP on the same spot after the penumbra formed. Results. The vertical component of the magnetic field, B ver , at the umbra-penumbra boundary increases during penumbra formation owing to the incursion of the penumbra into umbral areas. After 2.5 h, the penumbra reaches a stable state as shown by the GFPI data. At this stable stage, the simultaneous Hinode/SP observations show a B ver value comparable to that of umbra-penumbra boundaries of fully fledged sunspots. Conclusions. We confirm that the umbra-penumbra boundary, traditionally defined by an intensity threshold, is also characterised by a distinct canonical magnetic property, namely by B stable ver . During the penumbra formation process, the inner penumbra extends into regions where the umbra previously prevailed. Hence, in areas where B ver < B stable ver , the magneto-convection mode operating in the umbra turns into a penumbral mode. Eventually, the inner penumbra boundary settles at B stable ver , which hints toward the role of B stable ver as inhibitor of the penumbral mode of magneto-convection.

show abstract

Section: The Forming Up Boundary Vs the Stable Up Boundarysupporting

confidence: 92%

A distinct magnetic property of the inner penumbral boundary

Jurčák

González

Schlichenmaier

et al. 2015

A&A

View full text Add to dashboard Cite

show abstract

“…12b, we show the apparent flows found from the G-band filtergrams. The motion pattern in the regular penumbra confirms previous studies: in the inner penumbra, there are motions towards the sunspot umbra, while one observes outward motions in the outer penumbra (see Wang & Zirin 1992;Sobotka et al 1999;Márquez et al 2006). Hereafter, motions opposite to the Evershed flow are referred to as inflows (inward motions) and flows in the direction of the Evershed flow as outflows (outward motions).…”

Section: Brightness and Apparent Motionssupporting

confidence: 88%

“…The histogram peaks around 0.2 km s −1 with maximum values reaching 1.5 km s −1 . The mean value of |U LCT | in the regular penumbra is 0.41 km s −1 , which is about 0.1 km s −1 lower than the values obtained by Márquez et al (2006) and Wang & Zirin (1992). The distribution of apparent motions of all pixels in the orphan penumbra is shown by dashed grey line in Fig.…”

Section: Brightness and Apparent Motionsmentioning

confidence: 57%

Orphan penumbrae: Submerging horizontal fields

Jurčák

Rubio

Sobotka

2014

A&A

View full text Add to dashboard Cite

Aims. We investigate the properties of orphan penumbrae, which are photospheric filamentary structures observed in active regions near polarity inversion lines that resemble the penumbra of regular sunspots but are not connected to any umbra. Methods. We use Hinode data from the Solar Optical Telescope to determine the properties of orphan penumbrae. Spectropolarimetric data are employed to obtain the vector magnetic field and line-of-sight velocities in the photosphere. Magnetograms are used to study the overall evolution of these structures, and G-band and Ca ii H filtergrams are to investigate their brightness and apparent horizontal motions.Results. Orphan penumbrae form between regions of opposite polarity in places with horizontal magnetic fields. Their magnetic configuration is that of Ω-shaped flux ropes. In the two cases studied here, the opposite-polarity regions approach each other with time and the whole structure submerges as the penumbral filaments disappear. Orphan penumbrae are very similar to regular penumbrae, including the existence of strong gas flows. Therefore, they could have a similar origin. The main difference between them is the absence of a "background" magnetic field in orphan penumbrae. This could explain most of the observed differences. Conclusions. The fast flows we detect in orphan penumbrae may be caused by the siphon flow mechanism. Based on the similarities between orphan and regular penumbrae, we propose that the Evershed flow is also a manifestation of siphon flows.

show abstract

“…We find it convenient to adopt as this boundary the line separating inward-and outward-moving grains in bright filaments, at about 60% of the radial distance from the inner to the outer edge of the penumbra (Sobotka et al 1999;Sobotka & Sütterlin 2001;Márquez et al 2006); this line divides the penumbra into two parts with roughly equal areas. The boundary between the umbra and the inner penumbra corresponds to a transition from isolated convective plumes (in the umbra) to elongated roll-like structures in the penumbra; such a transition arises naturally as a consequence of increasing inclination of the 9), for the three cases we have considered.…”

Section: Inner and Outer Penumbramentioning

confidence: 99%

“…Weiss et al 1990), with only a modest difference in field inclination between bright and dark filaments (apart from the dark cores). Márquez et al (2006) have exploited the technique of local correlation tracking in order to determine proper motions within the penumbra. They find apparent motions that converge on dark filaments in the inner penumbra and then move inward along them.…”

Section: Inner and Outer Penumbramentioning

confidence: 99%

Flux Pumping and Magnetic Fields in the Outer Penumbra of a Sunspot

Brummell

Tobias

Thomas

et al. 2008

Astrophysical Journal

View full text Add to dashboard Cite

The filamentary structure of a sunspot penumbra is believed to be magnetoconvective in origin. In the outer penumbra there is a difference in inclination of up to 30 Y40 between the magnetic fields associated with bright and dark filaments, and the latter fields plunge downward below the surface toward the edge of the spot. We have proposed that these fields are dragged downward by magnetic pumping caused by the external granular convection. In this paper we model this process in a more elaborate idealized configuration that includes the curvature force exerted by an arched magnetic field in addition to magnetic buoyancy, and demonstrate that magnetic pumping remains an efficient mechanism for holding flux submerged. We discuss the implications of these results for the magnetic structure of the outer penumbra. Subject headingg s: MHD -Sun: magnetic fields -Sun: photosphere -sunspots

show abstract

High‐Resolution Proper Motions in a Sunspot Penumbra

Cited by 21 publications

References 49 publications

A distinct magnetic property of the inner penumbral boundary

A distinct magnetic property of the inner penumbral boundary

Orphan penumbrae: Submerging horizontal fields

Flux Pumping and Magnetic Fields in the Outer Penumbra of a Sunspot

Contact Info

Product

Resources

About