Modelling the Longitudinal Asymmetry in Sunspot Emergence: The Role of the Wilson Depression

Watson, Fraser; Fletcher, L.; Dalla, S.; Marshall, Stephen

doi:10.1007/s11207-009-9420-z

Cited by 59 publications

(58 citation statements)

References 17 publications

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“…The latter curve demonstrates the presence of Wilson depression of the order of 100 km in the magnetised region, similar to that observed for sunspots. The Wilson depression in the MBP model is significantly less than that of sunspots (Solanki 1993;Watson et al 2009). The equipartition layer, as is evident from the figure, is located deeper than the continuum formation layer in the region of the strongest magnetic field.…”

Section: Static Bright Point Modelmentioning

confidence: 92%

A photospheric bright point model

Shelyag¹,

Mathioudakis

Keenan

et al. 2010

A&A

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Aims.A magneto-hydrostatic model is constructed with spectropolarimetric properties close to those of solar photospheric magnetic bright points. Methods. Results of solar radiative magneto-convection simulations are used to produce the spatial structure of the vertical component of the magnetic field. The horizontal component of magnetic field is reconstructed using the self-similarity condition, while the magneto-hydrostatic equilibrium condition is applied to the standard photospheric model with the magnetic field embedded. Partial ionisation processes are found to be necessary for reconstructing the correct temperature structure of the model. Results. The structures obtained are in good agreement with observational data. By combining the realistic structure of the magnetic field with the temperature structure of the quiet solar photosphere, the continuum formation level above the equipartition layer can be found. Preliminary results are shown of wave propagation through this magnetic structure. The observational consequences of the oscillations are examined in continuum intensity and in the Fe I 6302 Å magnetically sensitive line.

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Section: Static Bright Point Modelmentioning

confidence: 92%

A photospheric bright point model

Shelyag¹,

Mathioudakis

Keenan

et al. 2010

A&A

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“…In order to analyse the sunspots over solar cycle 23, the STARA (Sunspot Tracking And Recognition Algorithm) code developed by Watson et al (2009) was used, and readers are referred there for information on the method and its testing. This is an automated system for detecting and tracking sunspots through large datasets and also records physical parameters of the sunspots detected.…”

Section: Creating a Catalogue Of Sunspotsmentioning

confidence: 99%

“…It is the purpose of this article to detail some physical properties of sunspots detected in the continuum images from the SOHO/MDI instrument (Scherrer et al 1995) and how they vary throughout solar cycle 23. We have used an image processing algorithm based on mathematical morphology (Watson et al 2009). …”

Section: Introductionmentioning

confidence: 99%

Evolution of sunspot properties during solar cycle 23

Watson

Fletcher²,

Marshall³

2011

A&A

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Context. The long term study of the Sun is necessary if we are to determine the evolution of sunspot properties and thereby inform modeling of the solar dynamo, particularly on scales of a solar cycle. Aims. We aim to determine a number of sunspot properties over cycle 23 using the uniform database provided by the SOHO Michelson Doppler Imager data. We focus in particular on their distribution on the solar disk, maximum magnetic field and umbral/penumbral areas. We investigate whether the secular decrease in sunspot maximum magnetic field reported in Kitt Peak data is present also in MDI data. Methods. We have used the Sunspot Tracking And Recognition Algorithm (STARA) to detect all sunspots present in the SOHO Michelson Doppler Imager continuum data giving us 30 084 separate detections. We record information on the sunspot locations, area and magnetic field properties as well as corresponding information for the umbral areas detected within the sunspots, and track them through their evolution. Results. We find that the total visible umbral area is 20−40% of the total visible sunspot area regardless of the stage of the solar cycle. We also find that the number of sunspots observed follows the Solar Influences Data Centre international sunspot number with some interesting deviations. Finally, we use the magnetic information in our catalogue to study the long term variation of magnetic field strength within sunspot umbrae and find that it increases and decreases along with the sunspot number. However, if we were to assume a secular decrease as was reported in the Kitt Peak data and take into account sunspots throughout the whole solar cycle we would find the maximum umbral magnetic fields to be decreasing by 23.6 ± 3.9 Gauss per year, which is far less than has previously been observed by other studies (although measurements are only available for solar cycle 23). If we only look at the declining phase of cycle 23 we find the decrease in sunspot magnetic fields to be 70 Gauss per year.

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“…They found values of some 100 km in the penumbra and some 400 km in the umbra, with a fairly sharp transition at the umbra -penumbra boundary. In a more recent study, Watson et al (2009) compared observations of sunspot longitude distribution and Monte Carlo simulations of sunspot appearance using different models for spot growth rate, growth time and depth of Wilson depression, deducing a mean depth for the umbral τ = 1 layer of 500 -1500 km.…”

Section: The Wilson Depressionmentioning

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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Modelling the Longitudinal Asymmetry in Sunspot Emergence: The Role of the Wilson Depression

Cited by 59 publications

References 17 publications

A photospheric bright point model

A photospheric bright point model

Evolution of sunspot properties during solar cycle 23

Modeling the Subsurface Structure of Sunspots

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