Inversion of Stokes vector profiles in terms of a 3-component model

Bernasconi, P. N.; Solanki, S. K.

doi:10.1007/bf00146640

Cited by 9 publications

(6 citation statements)

References 11 publications

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“…7. It is possible to extend the Stokes fitting technique to encompass two magnetic components (Bernasconi &: Solanki, 1995) and thus model the effect of the canopy directly during the inversion. This may be a promising approach for the future.…”

Section: Discussionmentioning

confidence: 99%

The influence of sunspot canopies on magnetic inclination measurements in solar plages

1996

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Sunspots are known to have large, low-lying magnetic canopies, i.e. horizontal magnetic fields overlying a field-free medium, that cover substantial fractions of active region plage. In this paper we consider the influence of such canopies on the inclination of plage magnetic fields. We find that for observations in spectral lines like 5250.2/~ the neglect of a sunspot canopy when determining magnetic inclination angles of plage fields can introduce errors exceeding 5-10 ~ . This is particularly true if the observations do not have high spatial resolution. Thus this effect may explain some of the measurements of substantially inclined fields in solar plages. Furthermore we find that the Fe I 15648 line is far superior in giving correct flux-tube inclinations in the presence of a sunspot magnetic canopy. Finally, the inversion of full Stokes profiles is shown to produce more reliable results than results obtained by considering only ratios of individual Stokes profile parameters.Key words: Magnetic fields -active regions -plage -sunspots -flux tubes * Primed quantities, inclination angle V I and azimuth X/, refer to local solar coordinates, unprimed ones to inclinations and azimuths relative to the line of sight.

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Section: Discussionmentioning

confidence: 99%

The influence of sunspot canopies on magnetic inclination measurements in solar plages

1996

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“…These complex profiles have been ascribed to the presence of gradients along the LOS in the magnetic and thermodynamic parameters of the atmosphere (e.g., Solanki & Pahlke 1988;Sigwarth et al 1999;Khomenko et al 2003;Franz & Schlichenmaier 2013) or to the presence of several atmospheric components in a single spatial resolution element (e.g., Martínez Pillet et al 1997;Bernasconi & Solanki 1996;Fischer et al 2012).…”

Section: Model Selection and Inversionmentioning

confidence: 99%

Signatures of the impact of flare-ejected plasma on the photosphere of a sunspot light bridge

Felipe

Collados

Khomenko

et al. 2017

A&A

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Aims. We investigate the properties of a sunspot light-bridge, focusing on the changes produced by the impact of a plasma blob ejected from a C-class flare. Methods. We observed a sunspot in active region NOAA 12544 using spectropolarimetric raster maps of the four Fe i lines around 15655 Å with the GREGOR Infrared Spectrograph (GRIS), narrow-band intensity images sampling the Fe i 6173 Å line with the GREGOR Fabry-Pérot Interferometer (GFPI), and intensity broad band images in G-band and Ca ii H band with the High-resolution Fast Imager (HiFI). All these instruments are located at the GREGOR telescope at the Observatorio del Teide, Tenerife, Spain. The data cover the time before, during, and after the flare event. The analysis is complemented with Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI) data from the Solar Dynamics Observatory (SDO). The physical parameters of the atmosphere at differents heights were inferred using spectral-line inversion techniques. Results. We identify photospheric and chromospheric brightenings, heating events, and changes in the Stokes profiles associated to the flare eruption and the subsequent arrival of the plasma blob to the light bridge, after traveling along an active region loop. Conclusions. The measurements suggest that these phenomena are the result of reconnection events driven by the interaction of the plasma blob with the magnetic field topology of the light bridge.

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“…It is well established that these effects play a negligible role in the formation of the spectral features we are interested in Shchukina & Trujillo Bueno (2001). We did not consider, either, models with more than two components (e.g., Bernasconi & Solanki 1996;Beck et al 2007;Beck & Rezaei 2009) or statistical models in which the thermodynamic and/or magnetic properties of the atmosphere are given statistically (e.g., Sánchez Almeida et al 1996;Sánchez Almeida 1997;Carroll & Kopf 2007). These models have been introduced to explain some of the most complex observed features which are difficult or impossible to explain with the models considered here.…”

Section: Atmospheric Modelsmentioning

confidence: 99%

Model Selection for Spectropolarimetric Inversions

Ramos

Sainz

González

et al. 2012

ApJ

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Inferring magnetic and thermodynamic information from spectropolarimetric observations relies on the assumption of a parameterized model atmosphere whose parameters are tuned by comparison with observations. Often, the choice of the underlying atmospheric model is based on subjective reasons. In other cases, complex models are chosen based on objective reasons (for instance, the necessity to explain asymmetries in the Stokes profiles) but it is not clear what degree of complexity is needed. The lack of an objective way of comparing models has, sometimes, led to opposing views of the solar magnetism because the inferred physical scenarios are essentially different. We present the first quantitative model comparison based on the computation of the Bayesian evidence ratios for spectropolarimetric observations. Our results show that there is not a single model appropriate for all profiles simultaneously. Data with moderate signal-to-noise ratios (S/Ns) favor models without gradients along the line of sight. If the observations show clear circular and linear polarization signals above the noise level, models with gradients along the line are preferred. As a general rule, observations with large S/Ns favor more complex models. We demonstrate that the evidence ratios correlate well with simple proxies. Therefore, we propose to calculate these proxies when carrying out standard least-squares inversions to allow for model comparison in the future.

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Inversion of Stokes vector profiles in terms of a 3-component model

Cited by 9 publications

References 11 publications

The influence of sunspot canopies on magnetic inclination measurements in solar plages

The influence of sunspot canopies on magnetic inclination measurements in solar plages

Signatures of the impact of flare-ejected plasma on the photosphere of a sunspot light bridge

Model Selection for Spectropolarimetric Inversions

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