Observations of the forward scattering Hanle effect in the Ca i 4227   {\AA} line
  Chromospheric magnetic fields are notoriously diffcult to measure. The chromospheric lines are broad, while the fields are producing a minuscule Zeeman-effect polarization. A promising diagnostic alternative is provided by the forward-scattering Hanle effect, which can be recorded in chromospheric lines such as the He i 10830 {\AA} and the Ca i 4227 {\AA} lines. We present a set of spectropolarimetric observations of the full Stokes vector obtained near the center of the solar disk in the Ca i 4227 {\AA} line with the ZIMPOL polarimeter at the IRSOL observatory.We detect a number of interesting forward-scattering Hanle effect signatures, which we model successfully using polarized radiative transfer. Here we focus on the observational aspects, while a separate companion paper deals with the theoretical modeling. 
M. Bianda (1), R. Ramelli (1), L. S. Anusha (3), J. O. Stenflo (1,2),   K. N. Nagendra (3), R. Holzreuter (4,2), M. Sampoorn...
astro-ph.SR