Simultaneous measurement of line-of-sight (LOS) magnetic and velocity fields at the photosphere and chromosphere are presented. Fe I line at λ6569 and H α at λ6563 are used respectively for deriving the physical parameters at photospheric and chromospheric heights. The LOS magnetic field obtained through the centerof-gravity method show a linear relation between photospheric and chromospheric field for field strengths less than 700 G. But in strong field regions, the LOS magnetic field values derived from H α are much weaker than what one gets from the linear relationship and also from those expected from the extrapolation of the photospheric magnetic field. We discuss in detail the properties of magnetic field observed in H α from the point of view of observed velocity gradients. The bisector analysis of H α Stokes I profiles show larger velocity gradients in those places where strong photospheric magnetic fields are observed. These observations may support the view that the stronger fields diverge faster with height compared to weaker fields.

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The polarized radiative transfer equation is solved when angle‐dependent partial redistribution and non‐coherent electron scattering are included as line‐scattering mechanisms. A static atmosphere with plane parallel symmetry is assumed. Test calculations are used to illustrate the effects of the electron‐scattering coefficient, the thermalization parameter and the continuous absorption coefficient on the line polarization. Results of angle‐averaged and angle‐dependent redistribution functions are compared and it is shown that angle‐dependent functions should be used to model the wing polarization of optically thin lines. The lower the continuous absorption compared with the electron scattering, the higher the wing polarization.

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