Radiation transfer through a model sunspot

Landman, D. A.; Finn, G. D.

doi:10.1007/bf00174528

Cited by 5 publications

(6 citation statements)

References 2 publications

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“…• Landman and Finn (1979): Imposed an Evershed-type radial velocity distribution in the upper region of the spot atmosphere, in order to get a satisfactory continuum-intensity profile across the sunspot. However, relatively large values of the Evershed flow (i.e., close to 10 km s −1 ) were required to obtain a satisfactory temperature profile.…”

Section: Self-similar Fieldsmentioning

confidence: 99%

Modeling the Subsurface Structure of Sunspots

et al. 2010

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While sunspots are easily observed at the solar surface, determining their subsurface structure is not trivial. There are two main hypotheses for the subsurface structure of sunspots: the monolithic model and the cluster model. Local helioseismology is the only means by which we can investigate subphotospheric structure. However, as current linear inversion techniques do not yet allow helioseismology to probe the internal structure with sufficient confidence to distinguish between the monolith and cluster models, the development of physically realistic sunspot models are a priority for helioseismologists. This is because they are not only important indicators of the variety of physical effects that may influence helioseismic inferences in active regions, but they also enable detailed assessments of the validity of helioseismic interpretations through numerical forward modeling. In this article, we provide a critical review of the existing sunspot models and an overview of numerical methods employed to model wave propagation through model sunspots. We then carry out a helioseismic analysis of the sunspot in Active Region 9787 and address the serious inconsistencies uncovered by Gizon et al. (2009aGizon et al. ( , 2009b. We find that this sunspot is most probably associated with a shallow, positive wave-speed perturbation (unlike the traditional two-layer model) and that travel-time measurements are consistent with a horizontal outflow in the surrounding moat.

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Section: Self-similar Fieldsmentioning

confidence: 99%

Modeling the Subsurface Structure of Sunspots

et al. 2010

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“…Two approaches are promising: (1) Inverting the measured Stokes vector to obtain a model atmosphere (e.g., del Toro Iniesta et al 2001;Westendorp Plaza et al 2001a,b), or (2) comparing specific properties of the measured Stokes vector with synthetic profiles that stem from model atmospheres (e.g., Maltby 1964;Landman & Finn 1979;Skumanich & Lites 1987;Solanki & Montavon 1993;Sanchez Almeida et al 1996;Martínez Pillet 2000;Schlichenmaier & Collados 2001). In this contribution we have chosen the latter method.…”

Section: Introductionmentioning

confidence: 99%

Net circular polarization of sunspot penumbrae

Schlichenmaier¹,

Müller²,

Steiner³

et al. 2002

A&A

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Abstract. The net circular polarization, N, is used as a measure for the asymmetry of Stokes-V profiles: N ≡ V (λ) dλ, integrated over an absorption line. Exemplary for Fe I 630.2 nm and Fe I 1564.8 nm, we synthesize penumbral V -profiles that stem from a model atmosphere in which the Evershed flow is confined to horizontal flux tubes which are embedded in a magnetic field that has the same magnetic field strength as the flow channel, but is less inclined w.r.t. the surface normal. At the two points where a line-of-sight enters and leaves the flow channel, discontinuities in the inclination, γ, the velocity v, and the azimuth, φ, of the magnetic field vector w.r.t. the plane perpendicular to the line-of-sight produce V -asymmetries. Assuming an axially symmetric penumbra, we investigate the azimuthal dependence N(ψ) for a mid-penumbral radius. We find: (1) Without including anomalous dispersion, N(ψ) is symmetric w.r.t. the line that connects disk center to the center of the spot. (2) Including anomalous dispersion, this symmetry is broken. We demonstrate that this is due to the difference in azimuth, φ(ψ), between the flow channel and the background that varies along the penumbral circle. For Fe I 630.2 nm this effect is found to be of minor relevance leading to essentially symmetric N-maps, whereas strong asymmetries are predicted for Fe I 1564.8 nm. Our results provide an explanation for recent observational findings.

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“…In a further development, we may insert a solution, which compares favorably with observation, into Equation (5) to derive implications on the transport of energy that maintains thermodynamic equilibrium. The SchlQter-Temesvary model and the return-flux models are based on specific prescriptions of magnetic fields and they have been compared with observation (Landman and Finn, 1979;Flgt et aL, 1982). In these works, observational input determines the background atmosphere and the plasma conditions along the axis of the idealized sunspot, defining the temperature in terms ofp and p by the ideal gas law.…”

Section: Static Sunspot Modelsmentioning

confidence: 99%

“…A fine tuning of the magnetic field can adjust the ~ = 1 layer so as to remove or create a bright ring around the model sunspot. It follows that Landman and Finn (1979) could have removed their unwanted bright ring without changing their equilibrium in a major way. A relaxation of their self-similar magnetic-field geometry, as Pizzo pointed out, could achieve that result.…”

Section: Static Sunspot Modelsmentioning

confidence: 99%

Some recent developments in the theoretical dynamics of magnetic fields

Low

1985

Sol Phys

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This article describes recent developments in the theoretical investigation of magnetostatic equilibrium in the presence of gravity, nonequilibrium in hydromagnetics, and classical problems in hydromagnetic stability. The construction ofmagnetostatic equilibria has progressed beyond geometrically idealized systems, such as the axisymmetric system, to fully three-dimensional systems capable of modelling realistic solar structures. Nonequilibrium in a magnetic field with an arbitrary interweaving of lines of force due tb random footpoint motion is a novel and subtle property with important implications for the solar atmosphere. Work begun by Parker and subsequent developments are described. To the extent quasi-static solar structures are approximated by stable equilibrium, ideal hydromagnetic stability theory provides a first insight into how stability is achieved in the solar environment. A qualitative physical picture based on recent stability analyses is given. The article places emphasis on understanding basic principles and issues rather than detailed results which can be found in the published literature.

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Radiation transfer through a model sunspot

Cited by 5 publications

References 2 publications

Modeling the Subsurface Structure of Sunspots

Modeling the Subsurface Structure of Sunspots

Net circular polarization of sunspot penumbrae

Some recent developments in the theoretical dynamics of magnetic fields

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