Inversion of Stokes Profiles

Frutiger, C.; Solanki, S. K.; Fligge, M.; Bruls, J. H. M. J.

doi:10.1007/978-94-015-9329-8_22

Cited by 165 publications

(208 citation statements)

References 4 publications

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“…Stokes I, Q, U and V profiles of AR 10953 observed by the SOT/SP aboard Hinode were analysed using the SPINOR inversion code (Frutiger et al 2000), extended by van Noort (2012), to perform a spatially coupled 2D inversion, which removes the influence of the instrument's PSF in parallel with inverting the data.…”

Section: Discussionmentioning

confidence: 99%

Properties of solar plage from a spatially coupled inversion of Hinode SP data

Buehler

Lagg

Solanki

et al. 2015

A&A

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Aims. The properties of magnetic fields forming an extended plage region in AR 10953 were investigated. Methods. Stokes spectra of the Fe I line pair at 6302 Å recorded by the spectropolarimeter aboard the Hinode satellite were inverted using the SPINOR code. The code performed a 2D spatially coupled inversion on the Stokes spectra, allowing the retrieval of gradients in optical depth within the atmosphere of each pixel, whilst accounting for the effects of the instrument's PSF. Consequently, no magnetic filling factor was needed.Results. The inversion results reveal that plage is composed of magnetic flux concentrations (MFCs) with typical field strengths of 1520 G at log(τ) = −0.9 and inclinations of 10 • −15 • . The MFCs expand by forming magnetic canopies composed of weaker and more inclined magnetic fields. The expansion and average temperature stratification of isolated MFCs can be approximated well with an empirical plage thin flux tube model. The highest temperatures of MFCs are located at their edges in all log(τ) layers. Whilst the plasma inside MFCs is nearly at rest, each is surrounded by a ring of downflows of on average 2.4 km s −1 at log(τ) = 0 and peak velocities of up to 10 km s −1 , which are supersonic. The downflow ring of an MFC weakens and shifts outwards with height, tracing the MFC's expansion. Such downflow rings often harbour magnetic patches of opposite polarity to that of the main MFC with typical field strengths below 300 G at log(τ) = 0. These opposite polarity patches are situated beneath the canopy of their main MFC. We found evidence of a strong broadening of the Stokes profiles in MFCs and particularly in the downflow rings surrounding MFCs (expressed by a microturbulence in the inversion). This indicates the presence of strong unresolved velocities. Larger magnetic structures such as sunspots cause the field of nearby MFCs to be more inclined.

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Section: Discussionmentioning

confidence: 99%

Properties of solar plage from a spatially coupled inversion of Hinode SP data

Buehler

Lagg

Solanki

et al. 2015

A&A

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“…The data were inverted using the SPINOR inversion code (Frutiger 2000;Frutiger et al 2000), based on the STOPRO routines (Solanki 1987), in the spatially coupled mode described in A24, page 2 of 14 paper I. This technique takes the telescope diffraction directly into account in the inversion process.…”

Section: Inversionsmentioning

confidence: 99%

Peripheral downflows in sunspot penumbrae

Noort

Lagg

Tiwari

et al. 2013

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Context. Sunspot penumbrae show high-velocity patches along the periphery. Aims. The high-velocity downflow patches are believed to be the return channels of the Evershed flow. We aim to investigate their structure in detail using Hinode SOT/SP observations. Methods. We employ Fourier interpolation in combination with spatially coupled height dependent LTE inversions of Stokes profiles to produce high-resolution, height-dependent maps of atmospheric parameters of these downflows and investigate their properties. Results. High-speed downflows are observed over a wide range of viewing angles. They have supersonic line-of-sight velocities, some in excess of 20 km s −1 , and very high magnetic field strengths, reaching values of over 7 kG. A relation between the downflow velocities and the magnetic field strength is found, in good agreement with MHD simulations. Conclusions. The coupled inversion at high resolution allows for the accurate determination of small-scale structures. The recovered atmospheric structure indicates that regions with very high downflow velocities contain some of the strongest magnetic fields that have ever been measured on the Sun.

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“…For each resolution element of the simulation, the radiative transfer equation for polarized light was integrated along a vertical line of sight (corresponding to disk-center observations) with the SPINOR code (e.g., Frutiger et al 2000), using oscillator strengths taken from the VALD database (Piskunov et al 1995) and log ε = 7.46 for the iron abundance (Asplund 2000).…”

Section: Synthetic Observationsmentioning

confidence: 99%

On the relation between continuum brightness and magnetic field in solar active regions

Danilović

Röhrbein

Cameron

et al. 2013

A&A

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Context. Variations of solar irradiance are mainly determined by the changing coverage of the visible solar disk with magnetic flux concentrations. The relationship between brightness and field strength is an important ingredient for models and reconstructions of irradiance variations. Aims. We assess the effect of limited observational resolution on the relationship between brightness and magnetic field by comparing comprehensive MHD simulations with observational results. Methods. Simulations of magnetoconvection representing the near-surface layers of a plage region were used to determine maps of the continuum brightness and Stokes profiles for the Fe  line at 630.22 nm. After convolving with instrumental profiles, synthetic observations of the magnetic field were generated by applying a Stokes inversion code. We compare the resulting relation between brightness and apparent vertical magnetic field to the corresponding outcome derived from real observations of a plage region with the Hinode satellite. Results. Consideration of the image smearing effects due to the limited resolution of the observations transform the largely monotonic relation between brightness and field strength at the original resolution of the simulations into a profile with a maximum at intermediate field strength, which is in good agreement with the observations. Conclusions. Considering the effect of limited observational resolution renders the relation between brightness and magnetic field from comprehensive MHD simulations consistent with observational results. This is a necessary prerequisite for the utilization of simulations for models and reconstruction of solar irradiance variations.

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Inversion of Stokes Profiles

Cited by 165 publications

References 4 publications

Properties of solar plage from a spatially coupled inversion of Hinode SP data

Properties of solar plage from a spatially coupled inversion of Hinode SP data

Peripheral downflows in sunspot penumbrae

On the relation between continuum brightness and magnetic field in solar active regions

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