Three dimensional structure of a regular sunspot from the inversion of IR Stokes profiles

Mathew, Shibu K.; Lagg, A.; Solanki, S. K.; Collados, M.; Borrero, J. M.; Berdyugina, S. V.; Krupp, N.; Woch, J.; Frutiger, C.

doi:10.1051/0004-6361:20031282

Cited by 83 publications

(116 citation statements)

References 42 publications

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“…The total magnetic field strength decreases by about 2.2 G km −1 in the umbra and by 0.5 G km −1 in the penumbra. Our umbral value is smaller than that of Mathew, Lagg, Solanki, et al (1995). Looking at the vertical component B z , we find only a slightly smaller value in the umbra, while B z increases in the outer penumbra.…”

Section: Resultscontrasting

confidence: 79%

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The three-dimensional structure of the magnetic field of a sunspot

Balthasar¹,

Gömöry²

2008

Proc. IAU

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Abstract. Spectro-polarimetric observations in several spectral lines allow to determine the height variation of the magnetic field of a small sunspot throughout the solar photosphere. The full Stokes-vector is measured with high spatial resolution. From these data we derive the magnetic field vector. The magnetic field strength decreases with height everywhere in the spot, even in the outer penumbra where some other authors have reported the opposite. The precise value of this decrease depends on the exact position in the spot. Values vary between 0.5 and 2.2 G km −1 when they are determined from an iron and a silicon line in the near infrared. The magnetic field is less inclined in the higher layers where the silicon line is formed. Once the magnetic vector field is known, it is straight forward to determine current densities and helicities. Current densities exhibit a radial structure in the penumbra, although it is still difficult to correlate this with the structure seen in the intensity continuum. In spite of this, current densities have a potential to serve as diagnostic tools to understand the penumbra, at least with the spatial resolution of the upcoming telescopes. The mean infered helicity is negative, as expected for a spot in the northern hemisphere. Nevertheless, there are locations inside the spot with positive helicity.

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Section: Resultscontrasting

confidence: 79%

“…Looking at the vertical component B z , we find only a slightly smaller value in the umbra, while B z increases in the outer penumbra. The latter is explained by the high inclination to the vertical in the outer penumbra, and this inclination decreases with height, which is in contrast to Mathew, Lagg, Solanki, et al (1995).…”

Section: Resultsmentioning

confidence: 93%

The three-dimensional structure of the magnetic field of a sunspot

Balthasar¹,

Gömöry²

2008

Proc. IAU

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“…Similar models were provided by Mathew et al (2003Mathew et al ( , 2004) from the inversion of infrared Fe I spectral lines at 1.56 μm. Mathew et al (2004) also calculated maps of the Wilson depression and plasma parameter β.…”

Section: Penumbral Models and Spatially Resolved Modelsmentioning

confidence: 59%

“…However, the more recent observations of Mathew et al (2003) indicate that for regular isolated sunspots, the global azimuthal twist of the field does not significantly exceed 20°. Moreover, Yun (1971) and Osherovich and Flaa (1983) have included the effects of an azimuthal field twist in their (self-similar) sunspot models and find that the introduction of a moderately twisted field, compatible with observations, contributes little to the force balance in spots and only slightly changes the main characteristics of their sunspot models (e.g.…”

Section: Field Twistmentioning

confidence: 93%

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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“…The umbrae of the largest sunspots are the coolest structures observed in the solar photosphere, their temperature is some 2000 K lower than that of the quiet-Sun photosphere (Maltby et al 1986;Kopp & Rabin 1992;Balthasar & Schmidt 1993;Martinez Pillet & Vazquez 1993;Collados et al 1994). The orientation of the magnetic field is close to the local vertical in umbrae (Beckers & Schröter 1969;Keppens & Martinez Pillet 1996;Mathew et al 2003;Beck 2008).…”

Section: Introductionmentioning

confidence: 82%

Properties of sunspot umbrae observed in cycle 24

Kiess

Rezaei

Schmidt

2014

A&A

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Aims. There is an ongoing debate whether the solar activity cycle is overlaid with a long-term decline that may lead to another grand minimum in the near future. We used the size, intensity, and magnetic field strength of sunspot umbrae to compare the present cycle 24 with the previous one. Methods. We used data of the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory and selected all sunspots between May 2010 and October 2012, using one image per day. We created two subsets of this dataset with a manual tracking algorithm, both without duplication. One contains each sunspot (910 umbrae within 488 spots) and was used to analyze the distribution of umbral areas, selected with an automated thresholding method. The other subset contains 205 fully evolved sunspots. We estimated their magnetic field and the total magnetic flux and discuss the relations between umbral size, minimum continuum intensity, maximum field strength, and total magnetic flux. Results. We find non-linear relations between umbral minimum intensity and size and between maximum magnetic field strength and size. The field strength scales linearly with the intensity and the umbral size scales roughly linearly with the total magnetic flux, while the size and field strength level off with stronger flux. When separated into hemispheres and averaged temporally, the southern umbrae show a temporal increase in size and the northern umbrae remain constant. We detected no temporal variation in the umbral mean intensity. The probability density function of the umbral area in the ascending phase of the current solar cycle is similar to that of the last solar cycle. Conclusions. From our investigation of umbral area, magnetic field, magnetic flux, and umbral intensity of the sunspots of the rising phase of cycle 24, we do not find a significant difference to the previous cycle, and hence no indication for a long-term decline of solar activity.

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Three dimensional structure of a regular sunspot from the inversion of IR Stokes profiles

Cited by 83 publications

References 42 publications

The three-dimensional structure of the magnetic field of a sunspot

The three-dimensional structure of the magnetic field of a sunspot

Modeling the Subsurface Structure of Sunspots

Properties of sunspot umbrae observed in cycle 24

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