The three-dimensional structure of sunspots

Balthasar, H.; Muglach, K.

doi:10.1051/0004-6361/200912978

Cited by 18 publications

(17 citation statements)

References 34 publications

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“…Sobotka & Roudier (2007) determined that the moat radius is independent of the spot size. However, Balthasar & Muglach (2010) found that the moat flow terminates at a distance of four times the spot radius -in contrast to three times the spot radius in the present study. Extended statistical studies will help us to clarify this issue.…”

Section: Horizontal Proper Motionscontrasting

confidence: 99%

Horizontal flow fields observed in Hinode G-band images

Verma

Balthasar

Deng

et al. 2012

A&A

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Context. Generation and dissipation of magnetic fields is a fundamental physical process on the Sun. In comparison to flux emergence and the initial stages of sunspot formation, the demise of sunspots still lacks a comprehensive description. Aims. The evolution of sunspots is most commonly discussed in terms of their intensity and magnetic field. Here, we present additional information about the three-dimensional flow field in the vicinity of sunspots towards the end of their existence. Methods. We present a subset of multi-wavelengths observations obtained with the Japanese Hinode mission, the Solar Dynamics Observatory (SDO), and the Vacuum Tower Telescope (VTT) at Observatorio del Teide, Tenerife, Spain during the time period 2010 November 18−23. Horizontal proper motions were derived from G-band and Ca ii H images, whereas line-of-sight velocities were extracted from VTT echelle Hα λ656.28 nm spectra and Fe i λ630.25 nm spectral data of the Hinode/Spectro-Polarimeter, which also provided three-dimensional magnetic field information. The Helioseismic and Magnetic Imager on board SDO provided continuum images and line-of-sight magnetograms, in addition to the high-resolution observations for the entire disk passage of the active region. Results. We perform a quantitative study of photospheric and chromospheric flow fields in and around decaying sunspots. In one of the trailing sunspots of active region NOAA 11126, we observe moat flow and moving magnetic features (MMFs), even after its penumbra had decayed. We also detect a superpenumbral structure around this pore. We find that MMFs follow well-defined, radial paths from the spot all the way to the border of a supergranular cell surrounding the spot. In contrast, flux emergence near the other sunspot prevents the establishment of similar well ordered flow patterns, which could be discerned around a tiny pore of merely 2 Mm diameter. After the disappearance of the sunspots/pores, a coherent patch of abnormal granulation remained at their location, which was characterized by more uniform horizontal proper motions, low divergence values, and smaller photospheric Doppler velocities. This region, thus, differs significantly from granulation and other areas covered by G-band bright points. We conclude that this peculiar flow pattern is a signature of sunspot decay and the dispersal of magnetic flux.

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Section: Horizontal Proper Motionscontrasting

confidence: 99%

Horizontal flow fields observed in Hinode G-band images

Verma

Balthasar

Deng

et al. 2012

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“…However, an unusual case was reported by Zuccarello et al (2009) when several moving bipolar magnetic elements were observed moving away from a sunspot without penumbra. Also, observations show that the moving magnetic elements are not passively transported by the moat flow of plasma, and they can move faster than the plasma (Balthasar and Muglach, 2010). This is consistent with the sea-serpent behavior of the magnetic-field lines in the penumbra, which also produces moving bipolar elements, as was originally suggested by Harvey and Harvey (1973).…”

Section: Figuresupporting

confidence: 84%

Local Helioseismology of Sunspots: Current Status and Perspectives

Kosovichev

2012

Sol Phys

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Mechanisms of the formation and stability of sunspots are among the longeststanding and intriguing puzzles of solar physics and astrophysics. Sunspots are controlled by subsurface dynamics hidden from direct observations. Recently, substantial progress in our understanding of the physics of the turbulent magnetized plasma in strong-field regions has been made by using numerical simulations and local helioseismology. Both the simulations and helioseismic measurements are extremely challenging, but it becomes clear that the key to understanding the enigma of sunspots is a synergy between models and observations. Recent observations and radiative MHD numerical models have provided a convincing explanation to the Evershed flows in sunspot penumbrae. Also, they lead to the understanding of sunspots as self-organized magnetic structures in the turbulent plasma of the upper convection zone, which are maintained by a large-scale dynamics. Local helioseismic diagnostics of sunspots still have many uncertainties, some of which are discussed in this review. However, there have been significant achievements in resolving these uncertainties, verifying the basic results by new high-resolution observations, testing the helioseismic techniques by numerical simulations, and comparing results obtained by different methods. For instance, a recent analysis of helioseismology data from the Hinode space mission has successfully resolved several uncertainties and concerns (such as the inclined-field and phase-speed filtering effects) that might affect the inferences of the subsurface wave-speed structure of sunspots and the flow pattern. It becomes clear that for the understanding of the phenomenon of sunspots it is important to further improve the helioseismology methods and investigate the whole life cycle of active regions, from magnetic-flux emergence to dissipation. The Solar Dynamics Observatory mission has started to provide data for such investigations.

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“…In the two-hour averaged LCT flow maps, the overall impression of flow vectors for G-band and Ca ii H images is indistinguishable. The flow patterns around the satellite sunspot are different from regular sunspots (e.g., Balthasar & Muglach 2010) because of its nonradial penumbra and location within a complex active region. The most intriguing feature in the G-band flow maps is the anticlockwise spiral motion around the dominant umbral core N3.…”

Section: Flow Fields In Photosphere and Chromospherementioning

confidence: 94%

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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The three-dimensional structure of sunspots

Cited by 18 publications

References 34 publications

Horizontal flow fields observed in Hinode G-band images

Horizontal flow fields observed in Hinode G-band images

Local Helioseismology of Sunspots: Current Status and Perspectives

Horizontal flow fields observed in Hinode G-band images

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