Free access article

A&A 421, 741-754 (2004)
DOI: 10.1051/0004-6361:20047043

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

A. Vögler¹, J. H. M. J. Bruls² and M. Schüssler<sup>1

1</sup>  Max-Planck-Institut für Sonnensystemforschung (Formerly: Max-Planck-Institut für Aeronomie.) , Max-Planck-Strasse 2, 37191 Katlenburg-Lindau, Germany
²  Kiepenheuer-Institut für Sonnenphysik, Schöneckstrasse 6, 79104 Freiburg, Germany

(Received 9 January 2004 / Accepted 24 March 2004 )

Abstract
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.

Key words: Sun: photosphere -- radiative transfer -- methods: numerical

Offprint request: A. Vögler, avoegler@linmpi.mpg.de

© ESO 2004

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

• If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
• You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
• You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.