Solar cycle variation of sunspot intensity

Albregtsen, Fritz; Maltby, P.

doi:10.1007/bf00167551

Cited by 53 publications

(35 citation statements)

References 20 publications

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“…Deinzer, 1965;Yun, 1970) typically obtain lower temperatures for stronger magnetic fields. However, observations by Rossbach and Schröter (1970) and Albregtsen and Maltby (1981) indicated no dependence of umbral intensity on umbral size for umbral diameters greater than about 8 . On the other hand, the observations of Kopp and Rabin (1992) showed a nearly linear decrease in umbral brightness with umbral radius for six sunspots.…”

Section: Sunspot Thermodynamics In the Photospherementioning

confidence: 85%

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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: Sunspot Thermodynamics In the Photospherementioning

confidence: 85%

“…• Avrett (1981): Provided a combined model of the umbral photosphere, chromosphere, and transition zone, by combining the low photospheric model of Albregtsen and Maltby (1981) with the upper photospheric and chromospheric parts of the Lites and Skumanich (1982) model and the transition-region model of Nicolas et al (1981).…”

Section: Umbral Modelsmentioning

confidence: 99%

Modeling the Subsurface Structure of Sunspots

et al. 2010

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“…To define the umbra and penumbra, we produced at first an umbral mask using a variable threshold in continuum intensity. Using a fixed threshold did not produce satisfactory results because the umbral contrast varies with wavelength (e.g., Mattig 1971;Albregtsen & Maltby 1981;Chapman & Meyer 1981;Maltby et al 1986;Tritschler & Schmidt 2002). Using those (initial) masks, we constructed contours for the umbra and penumbra manually.…”

Section: Discussionmentioning

confidence: 99%

“…It was already known half a century ago that larger umbrae are darker and show higher magnetic field strength. Albregtsen & Maltby (1978) first reported a systematic variation in the umbral intensity in the infrared as a function of the solar cycle, with darker umbrae appearing in the early phase of the cycle (see also Albregtsen & Maltby 1981). Adjabshirzadeh & Koutchmy (1983) attributed this variation to the change in the number of umbral dots within the solar cycle.…”

Section: Introductionmentioning

confidence: 99%

Variation in sunspot properties between 1999 and 2011 as observed with the Tenerife Infrared Polarimeter

Rezaei

Beck

Schmidt

2012

A&A

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“…Therefore the umbral brightness of small spots and its wavelength dependence is almost unknown (Albregtsen & Maltby 1981b). Existing results refer to large sunspots (r u > 5 arcsec) and reveal no significant dependence between umbral core brightness and sunspot size (Zwaan 1965;Rossbach & Schröter 1970;Mykland 1973;Albregtsen & Maltby 1981a;Albregtsen et al 1984).…”

Section: Spectral Distribution Of Sunspot Intensitiesmentioning

confidence: 99%

Sunspot photometry with phase diversity

Tritschler

Schmidt

2002

A&A

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Abstract. The global brightness structure of a small sunspot is investigated. Seeing and instrumental effects are compensated by application of the phase-diversity technique and a conventional deconvolution method. We calculate brightness temperatures for the reconstructed data in three simultaneously observed continuum bands of the solar spectrum (402.1 nm, 569.5 nm, 709.1 nm). The darkest umbral regions are on average 0.17I , 0.27I and 0.32I bright. The corresponding temperatures lie in the range around 4790 K, 4600 K and 4460 K. The spatially averaged penumbral brightness amounts to 0.72I , 0.81I and 0.85I , which corresponds to 5910 K, 5750 K and 5640 K, respectively. Although the spectral distribution of the umbral and penumbral intensities is consistent with former measurements, the derived values support the idea that there exist a real difference in the thermal properties between the umbrae of small and large sunspots.

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Solar cycle variation of sunspot intensity

Cited by 53 publications

References 20 publications

Modeling the Subsurface Structure of Sunspots

Modeling the Subsurface Structure of Sunspots

Variation in sunspot properties between 1999 and 2011 as observed with the Tenerife Infrared Polarimeter

Sunspot photometry with phase diversity

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