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Astron. Astrophys. 350, 1018-1034 (1999)

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Two-dimensional simulation of solar granulation: description of technique and comparison with observations

A.S. Gadun 1, S.K. Solanki 2,3 and A. Johannesson 4

1 Main Astronomical Observatory of Ukrainian NAS, Goloseevo, 252650 Kiev-22, Ukraine
2 Institute of Astronomy, ETH, 8092 Zürich, Switzerland
3 Max-Planck-Institute of Aeronomy, Max-Planck-Strasse 2, 37191 Katlenburg-Lindau, Germany
4 Big Bear Solar Observatory, 264-33 Caltech, Pasadena CA 91125, USA

Received 22 September 1997 / Accepted 22 July 1999


The physical properties of the solar granulation are analyzed on the basis of 2-D fully compressible, radiation-hydrodynamic simulations and the synthetic spectra they produce. The basic physical and numerical treatment of the problem as well as tests of this treatment are described. The simulations are compared with spatially averaged spectral observations made near disk centre and high resolution spectra recorded near the solar limb. The present simulations reproduce a significant number of observed features, both at the centre of the solar disc and near the solar limb. Reproduced observables include the magnitude of continuum and line-core intensity fluctuations, line bisectors and correlations between different line parameters. Spatially averaged line shifts near disc centre, however, are not so well reproduced, as are individual correlations between line parameters near the solar limb. Possible causes of these discrepancies are discussed.

The present models predict the existence of two photospheric layers at which the temperature fluctuations change sign. We point out a diagnostic of the hitherto undetected upper sign reversal based on high spatial resolution spectral observations of a sample of lines formed over a wide range of heights in the photosphere.

Key words: hydrodynamics – line: formation – Sun: granulation – Sun: photosphere

Send offprint requests to: S.K. Solanki (solanki@astro.phys.ethz.ch)

© European Southern Observatory (ESO) 1999

Online publication: October 14, 1999