Surface Evolution of the Sun's Magnetic Field: A Historical Review of the Flux-Transport Mechanism

Sheeley, N. R.

doi:10.12942/lrsp-2005-5

Cited by 100 publications

(96 citation statements)

References 107 publications

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“…The latest phase of AR evolution is a subject of the flux transport models that have been brilliantly described in an historical context in another Living Review by Sheeley Jr (2005). These processes are crucial for the evolution of the solar cycle.…”

Section: Modelling the Evolution Of Ars From Emergence Through Decaymentioning

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: Modelling the Evolution Of Ars From Emergence Through Decaymentioning

confidence: 99%

Evolution of Active Regions

Driel-Gesztelyi

Green

2015

Living Rev. Sol. Phys.

265

131

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“…The technique described in the latter paper has been used with small modifications in a series of papers (Mackay, Gaizauskas, and van Ballegooijen, 2000;Mackay and van Ballegooijen, 2001, 2005, 2006, and is used again in this study. As carried out in Mackay, Gaizauskas, and van Ballegooijen (2000), the radial magnetic field component in the photosphere is taken as the initial boundary condition, and an initial potential coronal field extrapolated from it.…”

Section: Introductionmentioning

confidence: 99%

Modelling the Global Solar Corona: Filament Chirality Observations and Surface Simulations

2007

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Abstract.The hemispheric pattern of solar filaments is considered in the context of the global magnetic field of the solar corona. In recent work Mackay and van Ballegooijen have shown how, for a pair of interacting magnetic bipoles, the observed chirality pattern could be explained by the dominant range of bipole tilt angles and helicity in each hemisphere. This study aims to test this earlier result through a direct comparison between theory and observations, using newly-developed simulations of the actual surface and 3D coronal magnetic fields over a 6-month period, on a global scale.In this paper we consider two key components of the study; firstly the observations of filament chirality for the sample of 255 filaments, and secondly our new simulations of the large-scale surface magnetic field. Based on a flux-transport model, these will be used as the lower boundary condition for the future 3D coronal simulations. Our technique differs significantly from those of other authors, where the coronal field is either assumed to be purely potential, or has to be reset back to potential every 27 days in order that the photospheric field remain accurate. In our case we ensure accuracy by the insertion of newly-emerging bipolar active regions, based on observed photospheric synoptic magnetograms. The large-scale surface field is shown to remain accurate over the 6-month period, without any resetting. This new technique will enable future simulations to consider the long-term build-up and transport of helicity and shear in the coronal magnetic field, over many months or years.

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“…Nonetheless, the diffusivity in all cases falls short of the ∼600 km 2 s −1 required by semiempirical models to reproduce the migration of magnetic flux towards the poles and the polarity inversion with an 11 year cycle (Sheeley 2005) within the Babcock-Leighton model (Leighton 1964;Babcock 1961). Schrijver et al (1996) argue that there is, indeed, an observational bias towards the strongest magnetized, hence slower, magnetic features.…”

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confidence: 90%

Advection and dispersal of small magnetic elements in the very quiet Sun

Sainz

González

Ramos

2011

A&A

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We track small magnetic structures on very quiet regions (internetwork) of the Sun. We follow the footpoints of small-scale magnetic loops that appear on the photosphere at granular scales using spectropolarimetric and magnetographic data obtained with Hinode. We find two different regimes for their wanderings. Within granules (where they appear), they seem to be passively advected by the plasma -which is justified by their relatively low magnetic flux (∼10 16 Mx), and magnetic field strength (∼200 G). The plasma flow thus traced is roughly laminar with a characteristic mean velocity of 2 km s −1 and very low vorticity. Once the magnetic markers reach intergranular lanes, they remain there and are buffeted by the random flows of neighbouring granules and turbulent intergranules, follow random walks, and disperse across the solar surface with a diffusion constant of 195 km 2 s −1 . While on their intergranular random walking, they may fall close to whirlpools (on scales 400 km) associated with convective downdrafts, similar to the events recently reported in mesogranular and supergranular cell boundaries tracking magnetic bright points, which provides additional evidence that these events are ubiquitous on the solar surface.

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Surface Evolution of the Sun's Magnetic Field: A Historical Review of the Flux-Transport Mechanism

Cited by 100 publications

References 107 publications

Evolution of Active Regions

Evolution of Active Regions

Modelling the Global Solar Corona: Filament Chirality Observations and Surface Simulations

Advection and dispersal of small magnetic elements in the very quiet Sun

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