THE DETERMINATION OF THE SOLAR VECTOR MAGNETIC-FIELD AT THE SURFACE FROM STOKES PROFILES

A simple method is proposed to infer the vector magnetic field at the surface of the Sun from Stokes profiles. This is based on the assumpti on that the variations of thermodynamical and magnetic field parameter s with depth near the surface are so small that the displacements of t he wavelengths at which the Stokes profiles reach their extrema can be ignored. And hence the polarized radiative transfer equations are gre atly reduced to a set of non-linear equations with vector magnetic fie ld parameters (H, gamma, chi) which can be solved by a numerical itera tion method. By fitting the synthetic profiles, it is shown that this proposed method can produce information on the vector field at the sur face. It is also used to revise the observed profiles and it is found that the observed sunspot has the magnetic field structure of the fan model with the lines of magnetic field twisted.