Sunspots: An overview

Solanki, S. K.

doi:10.1007/s00159-003-0018-4

Cited by 648 publications

(517 citation statements)

References 6 publications

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“…Furthermore, the evolution of active regions includes two essential topics that have already been covered by other recent reviews: The sub-surface evolution and emergence of magnetic flux by Fan (2009), and the nature and evolution of sunspots by Solanki (2003). Instead of duplicating their work, where relevant, we refer the reader to specific parts of these insightful review articles.…”

Section: Definition Of Active Regionmentioning

confidence: 99%

Evolution of Active Regions

Driel-Gesztelyi

Green

2015

Living Rev. Sol. Phys.

234

127

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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: Definition Of Active Regionmentioning

confidence: 99%

Evolution of Active Regions

Driel-Gesztelyi

Green

2015

Living Rev. Sol. Phys.

234

127

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“…The aim here is to present a very general overview of some of the pertinent issues related to sunspot observations that need to be considered when developing a realistic sunspot model. Comprehensive reviews by Solanki (2003), Thomas and Weiss (2004), Tobias and Weiss (2004), Schlichenmaier (2009), and the books by Weiss (1992, 2008) (and references therein), have excellent extended discussions on both the observational and theoretical aspects of sunspots and active regions.…”

Section: Surface Observational Constraintsmentioning

confidence: 99%

“…A sunspot can span a lifetime of months, but more typically of weeks (Solanki, 2003). However, this life expectancy is considerably shorter than the magnetic diffusion time [t D = l 2 /η where l is the width of the current sheet and η = 1/σ is the magnetic diffusivity] across a solar active region where estimates for t D range from hundreds to thousands of years (e.g.…”

Section: Sunspot Formation and Decaymentioning

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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“…Their diameters, typically, are 5 100 Mm, and magnetic eld strengths are in the range 2 3 kG, sometimes reaching 4 5 kG [1,5,14]. Solar pores (i. e. small sunspots without penumbra) have diameters, typically, 1 3 Mm and magnetic eld of 1.5-2 kG.…”

Section: Introductionmentioning

confidence: 99%

Estimation of the flux tube diameters outside sunspots using Hinode observations. Preliminary results

Botygina

Gordovskyy

Lozitsky

2016

Adv.Astron.Spa.Physics

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Indirect estimations of diameters of the smallest ux tubes outside sunspots are made using SOT/Hinode observations of FeE 6301.5 and 6302.5 lines. These estimations are based on the comparison of measured e ective magnetic eld strength B eff in named lines. It is shown that B eff (6301.5)/B eff (6302.5) ≈ 1.3 in the range B eff = 40 300 G, and B eff (6301.5)/B eff (6302.5) ≈ 1.0 for B eff ≤ 10 20 G. The rst case corresponds to the two-component magnetic eld with kG ux tubes and weak background eld, whereas the second one corresponds to background eld without ux tubes. Assuming that the eld range B eff = 10 40 G corresponds to the case with only one ux tube in each pixel, the ux tube diameters should be 15 30 km. Possible in uence of the brightness contrast and the Zeeman saturation could change this estimation by approximately 20%.

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Sunspots: An overview

Cited by 648 publications

References 6 publications

Evolution of Active Regions

Evolution of Active Regions

Modeling the Subsurface Structure of Sunspots

Estimation of the flux tube diameters outside sunspots using Hinode observations. Preliminary results

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