FLUX-TUBE MODEL ATMOSPHERES AND STOKES V ZERO-CROSSING WAVELENGTHS

First results of the inversion of Stokes I and V profiles from plage r egions near disk center are presented. Both low and high spatial resol ution spectra of Fe I 6301.5 and Fe I 6302.5 Angstrom obtained with th e Advanced Stokes Polarimeter (ASP) have been considered for analysis. The thin flux-tube approximation, implemented in an LTE inversion cod e based on response functions, is used to describe unresolved magnetic elements. The code allows the simultaneous and consistent inference o f all atmospheric quantities determining the radiative transfer with t he sole assumption of hydrostatic equilibrium. By considering velocity gradients within the tubes, we are able to match the full ASP Stokes profiles. The magnetic atmospheres derived from the inversion are char acterized by the absence of significant motions in high layers and str ong velocity gradients in deeper layers. These are essential to reprod uce the asymmetries of the observed profiles. Our scenario predicts a shift of the Stokes V zero-crossing wavelengths, which is indeed prese nt in observations made with the Fourier Transform Spectrometer.