Sunspot Group Decay

Hathaway, David H.; Choudhary, Debi Prasad

doi:10.1007/s11207-008-9226-4

Cited by 73 publications

(88 citation statements)

References 22 publications

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“…• Photometric decay rates observed in the satellite sunspot are in good agreement with other studies (Bumba 1963;Moreno-Insertis & Vazquez 1988;Martínez Pillet et al 1993;Hathaway & Choudhary 2008). …”

Section: Discussionsupporting

confidence: 90%

Horizontal flow fields observed in Hinode G-band images

Verma

Denker

2012

A&A

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Context. Emergence of magnetic flux plays an important role in the initiation of flares. However, the role of submerging magnetic flux in prompting flares is more ambiguous, not the least because of the scarcity of observations. Aims. The flare-prolific active region NOAA 10930 offered both a developing δ-spot and a decaying satellite sunspot of opposite polarity. The objective of this study is to characterize the photometric decay of the satellite sunspot as well as the evolution of photospheric and chromospheric horizontal proper motions in its surroundings. Methods. We apply the local correlation tracking technique to a 16-h time-series of Hinode G-band and Ca ii H images and study the horizontal proper motions in the vicinity of the satellite sunspot on 2006 December 7. Decorrelation times were computed to measure the lifetime of solar features in intensity and flow maps. Results. We observed shear flows in the dominant umbral cores of the satellite sunspot. These flows vanished once the penumbra had disappeared. This slow penumbral decay had an average rate of 152 Mm 2 day −1 over an 11-h period. Typical lifetimes of intensity features derived from an autocorrelation analysis are 3-5 min for granulation, 25-35 min for G-band bright points, and up to 200−235 min for penumbrae, umbrae, and pores. Long-lived intensity features (i.e., the dominant umbral cores) are not related to long-lived flow features in the northern part of the sunspot, where flux removal, slowly decaying penumbrae, and persistent horizontal flows of up to 1 km s −1 contribute to the erosion of the sunspot. Finally, the restructuring of magnetic field topology was responsible for a homologous M2.0 flare, which shared many characteristics with an X6.5 flare on the previous day. Conclusions. Notwithstanding the prominent role of δ-spots in flaring, we conclude based on the decomposition of the satellite sunspot, the evolution of the surrounding flow fields, and the timing of the M2.0 flare that the vanishing magnetic flux in the decaying satellite sunspot played an instrumental role in triggering the homologous M2.0 flare and the eruption of a small Hα filament. The strong magnetic field gradients of the neighboring δ-spot merely provided the vehicle for the strongest flare emission about 10 min after the onset of the flare.

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Section: Discussionsupporting

confidence: 90%

Horizontal flow fields observed in Hinode G-band images

Verma

Denker

2012

A&A

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“…There is a notable asymmetry in the time spent by an active region in emergence and decay: emergence lasts for hours to days (≤ 5 days; Harvey, 1993), while the decay of spots may last from days to several weeks (e.g., Hathaway and Choudhary, 2008) and even in some cases months (van Driel-Gesztelyi et al, 1999a). Once all the magnetic flux has emerged, or possibly even before that (McIntosh, 1981;, active regions start to decay.…”

Section: Lifetime Of Sunspotsmentioning

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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“…They were measured from 1874 to 1976 (Baumann & Solanki 2005) and from 1977 to 2007 (Hathaway & Choudhary 2008). These sizes follow a log-normal distribution up 3000 MSH, but there are a few larger groups.…”

Section: Excluding Unobserved Regions In the Parameter Spacementioning

confidence: 99%

The standard flare model in three dimensions

Aulanier

Démoulin

Schrijver

et al. 2012

A&A

202

144

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Context. Solar flares strongly affect the Sun's atmosphere as well as the Earth's environment. Quantifying the maximum possible energy of solar flares of the present-day Sun, if any, is thus a key question in heliophysics. Aims. The largest solar flares observed over the past few decades have reached energies of a few times 10 32 erg, possibly up to 10 33 erg. Flares in active Sun-like stars reach up to about 10 36 erg. In the absence of direct observations of solar flares within this range, complementary methods of investigation are needed to assess the probability of solar flares beyond those in the observational record. Methods. Using historical reports for sunspot and solar active region properties in the photosphere, we scaled to observed solar values a realistic dimensionless 3D MHD simulation for eruptive flares, which originate from a highly sheared bipole. This enabled us to calculate the magnetic fluxes and flare energies in the model in a wide paramater space. Results. Firstly, commonly observed solar conditions lead to modeled magnetic fluxes and flare energies that are comparable to those estimated from observations. Secondly, we evaluate from observations that 30% of the area of sunspot groups are typically involved in flares. This is related to the strong fragmentation of these groups, which naturally results from sub-photospheric convection. When the model is scaled to 30% of the area of the largest sunspot group ever reported, with its peak magnetic field being set to the strongest value ever measured in a sunspot, it produces a flare with a maximum energy of ∼6 × 10 33 erg. Conclusions. The results of the model suggest that the Sun is able to produce flares up to about six times as energetic in total solar irradiance fluence as the strongest directly observed flare of Nov. 4, 2003. Sunspot groups larger than historically reported would yield superflares for spot pairs that would exceed tens of degrees in extent. We thus conjecture that superflare-productive Sun-like stars should have a much stronger dynamo than in the Sun.

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Sunspot Group Decay

Cited by 73 publications

References 22 publications

Horizontal flow fields observed in Hinode G-band images

Horizontal flow fields observed in Hinode G-band images

Evolution of Active Regions

The standard flare model in three dimensions

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