J. H. M. J. Bruls

Approximations for non-grey radiative transfer in numerical simulations of the solar photosphere

Realistic simulations of solar (magneto-)convection require an accurate treatment of the non-grey character of the radiative energy transport. Owing to the large number of spectral lines in the solar atmosphere, statistical representations of the line opacities have to be used in order to keep the problem numerically tractable. We consider two statistical approaches, the opacity distribution function (ODF) concept and the multigroup (or opacity binning) method and provide a quantitative assessment of the errors that arise from the application of these methods in the context of 2D/3D simulations. In a first step, the ODF- and multigroup methods are applied to a 1D model-atmosphere and the resulting radiative heating rates are compared. A number of 4−6 frequency bins is found to warrant a satisfactory modeling of the radiative energy exchange. Further tests in 2D model-atmospheres show the applicability of the multigroup method in realistic situations and underline the importance of a non-grey treatment. Furthermore, we address the question of an appropriate opacity average in multigroup calculations and discuss the significance of velocity gradients for the radiative heating rates.

Relation between photospheric magnetic field and chromospheric emission

Aims. We investigate the relationship between the photospheric magnetic field and the emission of the mid chromosphere of the Sun. Methods. We simultaneously observed the Stokes parameters of the photospheric iron line pair at 630.2 nm and the intensity profile of the chromospheric

Carbon monoxide in the solar atmosphere - I. Numerical method and two-dimensional models

\ion{Ca}{ii}

Photospheric ne structure: An observational challenge An analysis of radiative transfer eects on the visibility of small-scale structures

 H line at 396.8 nm in a quiet Sun region at a heliocentric angle of 53°. Various line parameters have been deduced from the

Inversion of Stokes Profiles

\ion{Ca}{ii}

Apparent solar radius variations - The influence of magnetic network and plage

 H line profile. The photospheric magnetic field vector has been reconstructed from an inversion of the measured Stokes profiles. After alignment of the Ca and Fe maps, a common mask has been created to define network and inter-network regions. We perform a statistical analysis of network and inter-network properties. The H -index is the integrated emission in a 0.1 nm band around the Ca core. We separate a non-magnetically,

Calculation of Spectral Darkening and Visibility Functions for Solar Oscillations

H_{{\rm non}}

The Upper Photosphere and Lower Chromosphere of Small-Scale Magnetic Features

, and a magnetically,

Simulation of Solar Radiative Magneto-Convection

H_{{\rm mag}}

The Granulation Sensitivity Of Neutral Metal Lines

, heated component from a non-heated component,