Speaker: H. Frisch
Institute: Observatoire de la Cote d'Azur, Nice, France
Date & Time: September 24th, 2009, 10:00 a.m.
Place: A135
Organizer: Huairou Solar Observing Station
Abstract：In spite of great progress in the resolving power of instruments, much of the magnetic structure in the solar atmosphere remains and will always remain unresolved, in particular because of the integration along the line of sight. To overcome this difficulty, it is in general assumed that the magnetic structures are optically thin or optically thick, i.e. that they have dimensions that are either much smaller or much larger than the photon mean-free-paths. In both cases, the mean Stokes parameters averaged over the magnetic field vector Probability Distribution Function (PDF) can be calculated with a polarized transfer equation having deterministic coefficients. To take into account magnetic field structures that have an optical depth around unity, it is necessary to solve polarized radiative transfer equations with random coefficients, a much harder task.
I shall describe some methods that have been developed to calculate the mean Stokes parameters for a random magnetic field modeled by a piece wise constant Markov process with a finite correlation length. The optically thin and optically thick limits are recovered when the correlation length goes to zero or to infinity. I shall show on some examples the sensitivity of the mean Stokes parameters to the magnetic field correlation length and PDF.
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