Streaming Magnetic Features near Sunspots

Vrabec, Dale

doi:10.1007/978-94-010-2103-6_26

Cited by 47 publications

(14 citation statements)

References 38 publications

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“…Despite the inherent difficulties in quantitative studies of MMFs, due to their small spatial scale, short lifetimes (few hours, Vrabec, 1974) and ability to merge, the idea that MMFs transport flux away from the spot at the same rate at which flux in the spot is decreasing has been suggested and accepted by many. However, conclusive evidence that all MMFs are indeed detaching flux from the periphery of the spot at the photospheric or sub-photospheric level has not yet been provided.…”

Section: Moving Magnetic Featuresmentioning

confidence: 99%

Evolution of Active Regions

Driel-Gesztelyi

Green

2015

Living Rev. Sol. Phys.

265

131

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The evolution of active regions (AR) from their emergence through their long decay process is of fundamental importance in solar physics. Since large-scale flux is generated by the deepseated dynamo, the observed characteristics of flux emergence and that of the subsequent decay provide vital clues as well as boundary conditions for dynamo models. Throughout their evolution, ARs are centres of magnetic activity, with the level and type of activity phenomena being dependent on the evolutionary stage of the AR. As new flux emerges into a pre-existing magnetic environment, its evolution leads to re-configuration of small-and large-scale magnetic connectivities. The decay process of ARs spreads the once-concentrated magnetic flux over an ever-increasing area. Though most of the flux disappears through small-scale cancellation processes, it is the remnant of large-scale AR fields that is able to reverse the polarity of the poles and build up new polar fields. In this Living Review the emphasis is put on what we have learned from observations, which is put in the context of modelling and simulation efforts when interpreting them. For another, modelling-focused Living Review on the sub-surface evolution and emergence of magnetic flux see Fan (2009). In this first version we focus on the evolution of dominantly bipolar ARs. Article RevisionsLiving Reviews supports two ways of keeping its articles up-to-date:Fast-track revision. A fast-track revision provides the author with the opportunity to add short notices of current research results, trends and developments, or important publications to the article. A fast-track revision is refereed by the responsible subject editor. If an article has undergone a fast-track revision, a summary of changes will be listed here.Major update. A major update will include substantial changes and additions and is subject to full external refereeing. It is published with a new publication number.For detailed documentation of an article's evolution, please refer to the history document of the article's online version at http://dx

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Section: Moving Magnetic Featuresmentioning

confidence: 99%

Evolution of Active Regions

Driel-Gesztelyi

Green

2015

Living Rev. Sol. Phys.

265

131

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“…When the flux does emerge, it is often in the form of pore structures of the order of a Mm or so in size (Vrabec, 1974;Zwaan, 1978Zwaan, , 1992McIntosh, 1981). Pores have continuum intensities ranging from 80% down to 20% of the normal photospheric intensity, with maximum magnetic-field strengths of 1500 -2000 G. If a growing pore reaches a sufficient size (a diameter of about 3500 km, but sometimes as much as 7000 km) or a sufficient total magnetic flux of order 10 20 Mx (Leka and Skumanich, 1998), and if the magnetic field reaches an inclination from the vertical that is greater than about γ = 35°( Martínez Pillet, 1997), then it forms a penumbra at its periphery and becomes a fullfledged sunspot.…”

Section: Sunspot Formation and Decaymentioning

confidence: 99%

“…The flow usually persists over the duration of the spot's life, while the area and magnetic flux of the sunspot decrease at a roughly constant rate. As the moat flow evolves, it pushes the magnetic flux to its periphery, leaving the moat largely free of magnetic field except for small magnetic features (known as moving magnetic features) that move outward across the moat at speeds of about 1 km s −1 (Sheeley, 1969(Sheeley, , 1972Vrabec, 1971Vrabec, , 1974Harvey and Harvey, 1973;Brickhouse and Labonte, 1988;Wang and Zirin, 1992;Yurchyshyn, Wang, and Goode, 2001;Sainz Dalda and Bellot Rubio, 2008a).…”

Section: Moat Flow and Moving Magnetic Featuresmentioning

confidence: 99%

Modeling the Subsurface Structure of Sunspots

et al. 2010

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While sunspots are easily observed at the solar surface, determining their subsurface structure is not trivial. There are two main hypotheses for the subsurface structure of sunspots: the monolithic model and the cluster model. Local helioseismology is the only means by which we can investigate subphotospheric structure. However, as current linear inversion techniques do not yet allow helioseismology to probe the internal structure with sufficient confidence to distinguish between the monolith and cluster models, the development of physically realistic sunspot models are a priority for helioseismologists. This is because they are not only important indicators of the variety of physical effects that may influence helioseismic inferences in active regions, but they also enable detailed assessments of the validity of helioseismic interpretations through numerical forward modeling. In this article, we provide a critical review of the existing sunspot models and an overview of numerical methods employed to model wave propagation through model sunspots. We then carry out a helioseismic analysis of the sunspot in Active Region 9787 and address the serious inconsistencies uncovered by Gizon et al. (2009aGizon et al. ( , 2009b. We find that this sunspot is most probably associated with a shallow, positive wave-speed perturbation (unlike the traditional two-layer model) and that travel-time measurements are consistent with a horizontal outflow in the surrounding moat.

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“…These culls might constitute a substantial amount of sunspots' flux outflow. As Vrabec [5] has commented, the magnetic flux outflow is a "considerably more complicated process than" fragmentation of sunspots into MMFs. Further investigations using higher resolution data and estimation methods need to be carried out to estimate the flux outflow.…”

Section: Resultsmentioning

confidence: 99%

Tracking moving magnetic features in the photosphere

Büchner

Zhang

2009

Sci. China Ser. G-Phys. Mech. Astron.

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sun, activity, magnetic fields, photosphere, sunspots, moat, moving magnetic features On magnetograms, small-scale Moving Magnetic Features (MMFs) of both the same and opposite to the sunspots' magnetic field are observed to originate near the penumbra boundary and stream almost radially outward within the moat at a speed about 1 km/s and finally disappear in the moat or merge into the surrounding network. This flux outflow plays an intricate role in the mass and magnetic energy flow around sunspots and contributes to the evolution of the sunspots. MMFs can be bipolar or unipolar. Observing MMFs requires consecutive, short time-cadence, and high

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Streaming Magnetic Features near Sunspots

Cited by 47 publications

References 38 publications

Evolution of Active Regions

Evolution of Active Regions

Modeling the Subsurface Structure of Sunspots

Tracking moving magnetic features in the photosphere

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