Magnetic Structure of Sunspots

Borrero, J. M.; Ichimoto, Kiyoshi

doi:10.12942/lrsp-2011-4

Cited by 213 publications

(236 citation statements)

References 229 publications

(401 reference statements)

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“…Indeed, the umbra of sunspots do require some level of convection to maintain their temperature of ∼ 4000 K and sub-structure in the form of umbral dots -bright spots -indicates small patches of enhanced temperature plasma where convection is thought to be occurring. For a more detailed discussion on the physical drivers of umbral dots see the Living Review by Borrero and Ichimoto (2011).…”

Section: Fragmentation Of Sunspots and The Re-establishment Of Convecmentioning

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: Fragmentation Of Sunspots and The Re-establishment Of Convecmentioning

confidence: 99%

Evolution of Active Regions

Driel-Gesztelyi

Green

2015

Living Rev. Sol. Phys.

265

131

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“…1). The latter is a filamentary structure of weaker, more horizontal magnetic field which surrounds the more vertically oriented stronger umbral magnetic field (Solanki 2003;Borrero and Ichimoto 2011, for reviews see). Typically, magnetic field strengths of about 1 kG are found in penumbrae while the maximum umbral field strengths usually range between 2 and 4 kG (Title et al 1993;Lites et al 1993;Schad 2013).…”

Section: Temporal Evolution Of the Magnetic Fieldmentioning

confidence: 99%

The magnetic field in the solar atmosphere

Wiegelmann

Thalmann

Solanki

2014

Astron Astrophys Rev

182

125

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This publication provides an overview of magnetic fields in the solar atmosphere with the focus lying on the corona. The solar magnetic field couples the solar interior with the visible surface of the Sun and with its atmosphere. It is also responsible for all solar activity in its numerous manifestations. Thus, dynamic phenomena such as coronal mass ejections and flares are magnetically driven. In addition, the field also plays a crucial role in heating the solar chromosphere and corona as well as in accelerating the solar wind. Our main emphasis is the magnetic field in the upper solar atmosphere so that photospheric and chromospheric magnetic structures are mainly discussed where relevant for higher solar layers. Also, the discussion of the solar atmosphere and activity is limited to those topics of direct relevance to the magnetic field. After giving a brief overview about the solar magnetic field in general and its global structure, we discuss in more detail the magnetic field in active regions, the quiet Sun and coronal holes.

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“…This assumption stems from the polarimetric observations of umbrae invariably finding the field inclination to be very close to vertical, at least in its central parts (Solanki 2003;Borrero & Ichimoto 2011). Radiative transfer calculations of vertical simulated model umbra atmospheres, with pre-set fields and a piston (Bard & Carlsson 2010), accurately reproduce the saw toothedlike pattern of alternating blue-and red-shifted emitting features, which are observed in the spectra of Ca ii H umbral flashes (Rouppe van der Voort et al 2003;Tian et al 2014).…”

Section: Introductionmentioning

confidence: 99%

Stable umbral chromospheric structures

Henriques

Scullion

Mathioudakis

et al. 2015

A&A

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Aims. We seek to understand the morphology of the chromosphere in sunspot umbra. We investigate if the horizontal structures observed in the spectral core of the Ca ii H line are ephemeral visuals caused by the shock dynamics of more stable structures, and examine their relationship with observables in the H-alpha line.Methods. Filtergrams in the core of the Ca ii H and H-alpha lines as observed with the Swedish 1-m Solar Telescope are employed.We utilise a technique that creates composite images and tracks the flash propagation horizontally. Results. We find 0. 15 wide horizontal structures, in all of the three target sunspots, for every flash where the seeing is moderate to good. Discrete dark structures are identified that are stable for at least two umbral flashes, as well as systems of structures that live for up to 24 min. We find cases of extremely extended structures with similar stability, with one such structure showing an extent of 5 . Some of these structures have a correspondence in H-alpha, but we were unable to find a one-to-one correspondence for every occurrence. If the dark streaks are formed at the same heights as umbral flashes, there are systems of structures with strong departures from the vertical for all three analysed sunspots.Conclusions. Long-lived Ca ii H filamentary horizontal structures are a common and likely ever-present feature in the umbra of sunspots. If the magnetic field in the chromosphere of the umbra is indeed aligned with the structures, then the present theoretical understanding of the typical umbra needs to be revisited.

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Magnetic Structure of Sunspots

Cited by 213 publications

References 229 publications

Evolution of Active Regions

Evolution of Active Regions

The magnetic field in the solar atmosphere

Stable umbral chromospheric structures

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