Modeling the Subsurface Structure of Sunspots

Moradi, Hamed; Baldner, Charles; Birch, A. C.; Braun, D. C.; Cameron, R. H.; Duvall, T. L.; Gizon, Laurent; Haber, D. A.; Hanasoge, Shravan M.; Hindman, Bradley W.; Jackiewicz, Jason; Khomenko, E.; Komm, R.; Rajaguru, S. P.; Rempel, Matthias; Roth, M.; Schlichenmaier, R.; Schunker, Hannah; Spruit, H. C.; Strassmeier, K. G.; Thompson, M. J.; Zharkov, S.

doi:10.1007/s11207-010-9630-4

Cited by 105 publications

(100 citation statements)

References 257 publications

(408 reference statements)

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“…Without such investigation it is premature to conclude that this inconsistency shows a failure of the local helioseismology inversions, as this was suggested by Gizon et al (2009). Based on these results, Moradi et al (2010) suggested that the sunspot in AR 9787 is most probably associated with a shallow, positive wave-speed perturbation (unlike the traditional two-layer model).…”

Section: Comparison Of Local Helioseismology Resultsmentioning

confidence: 94%

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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Section: Comparison Of Local Helioseismology Resultsmentioning

confidence: 94%

Local Helioseismology of Sunspots: Current Status and Perspectives

Kosovichev

2012

Sol Phys

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“…Numerical and theoretical modelling of acoustic-wave packet propagation through a magnetised plasma (Cally, 2000;Schunker and Cally, 2006;Shelyag, Zharkov, Fedun et al, 2009;Moradi, Baldner, Birch et al, 2010;Felipe, Khomenko, and Collados, 2010, for example) shows that acoustic waves when passing through magnetic-flux tube transform into different types of magneto-acoustic waves, which we then expect to find in sunspots. Mode conversion between various magneto-acoustic waves takes place around the region where the ambient sound speed [c] equals the Alfven velocity [a] which is situated near the surface in sunspots.…”

Section: Discussionmentioning

confidence: 99%

Properties of the 15 February 2011 Flare Seismic Sources

et al. 2012

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The first near-side X-class flare of the Solar Cycle 24 occurred in February 2011 and produced a very strong seismic response in the photosphere. One sunquake was reported by Kosovichev (2011) followed by the discovery of a second sunquake by Zharkov et al (2011). The flare had a two-ribbon structure and was associated with a flux rope eruption and a halo coronal mass ejection (CME) as reported in the CACTus catalogue. Following the discovery of the second sunquake and the spatial association of both sources with the locations of the feet of the erupting flux rope (Zharkov et al 2011) we present here a more detailed analysis of the observed photospheric changes in and around the seismic sources. These sunquakes are quite unusual, taking place early in the impulsive stage of the flare, with the seismic sources showing little hard X-ray (HXR) emission, and strongest X-ray emission sources located in the flare ribbons. We present a directional time--distance diagram computed for the second source, which clearly shows a ridge corresponding to the travelling acoustic wave packet and find that the quake at the second source happened about 45 seconds to one minute earlier than the first source. Using acoustic holography we report different frequency responses of the two sources. We find strong downflows at both seismic locations and a supersonic horizontal motion at the second site of acoustic wave excitation.Comment: 15 pages, 5 figures, accepted for publication by Solar Physic

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“…Sunspots enable us to trace differential rotation and meridional circulation on the solar surface to extreme precision as well as to measure in detail a surface magnetic field in full three dimensions (e.g., Solanki 2003;Moradi et al 2010). Sunspots are understood as the emergence of magnetic flux tubes originating from a dynamo process in the interior (Babcock 1961;Leighton 1964;Stix 1989), in mean-field terms referred to as the so-called αΩ-dynamo.…”

Section: Introductionmentioning

confidence: 99%

Spot evolution on the red giant star XX Triangulum

Künstler

Carroll

Strassmeier

2015

A&A

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Context. Solar spots appear to decay linearly proportional to their size. The decay rate of solar spots is directly related to magnetic diffusivity, which itself is a key quantity for the length of a magnetic-activity cycle. Is a linear spot decay also seen on other stars, and is this in agreement with the large range of solar and stellar activity cycle lengths? Aims. We investigate the evolution of starspots on the rapidly-rotating (P rot ≈ 24 d) K0 giant XX Tri, using consecutive time-series Doppler images. Our aim is to obtain a well-sampled movie of the stellar surface over many years, and thereby detect and quantify a starspot decay law for further comparison with the Sun. Methods. We obtained continuous high-resolution and phase-resolved spectroscopy with the 1.2-m robotic STELLA telescope on Tenerife over six years, and these observations are ongoing. For each observing season, we obtained between 5 to 7 independent Doppler images, one per stellar rotation, making up a total of 36 maps. All images were reconstructed with our line-profile inversion code iMap. A wavelet analysis was implemented for denoising the line profiles. To quantify starspot area decay and growth, we match the observed images with simplified spot models based on a Monte Carlo approach. Results. It is shown that the surface of XX Tri is covered with large high-latitude and even polar spots and with occasional small equatorial spots. Just over the course of six years, we see a systematically changing spot distribution with various timescales and morphology, such as spot fragmentation and spot merging as well as spot decay and formation. An average linear decay of D = −0.022 ± 0.002 SH/day is inferred. We found evidence of an active longitude in phase toward the (unseen) companion star. Furthermore, we detect a weak solar-like differential rotation with a surface shear of α = 0.016 ± 0.003. From the decay rate, we determine a turbulent diffusivity of η T = (6.3 ± 0.5) × 10 14 cm 2 /s and predict a magnetic activity cycle of ≈26 ± 6 yr. Finally, we present a short movie of the spatially resolved surface of XX Tri.

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Modeling the Subsurface Structure of Sunspots

Cited by 105 publications

References 257 publications

Local Helioseismology of Sunspots: Current Status and Perspectives

Local Helioseismology of Sunspots: Current Status and Perspectives

Properties of the 15 February 2011 Flare Seismic Sources

Spot evolution on the red giant star XX Triangulum

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