  The Hanle effect in strong spectral lines is the physical mechanism that
should be increasingly exploited for quantitative explorations of the magnetism
of the quiet solar chromospheric plasma. Here we show, by means of multilevel
radiative transfer calculations and new spectropolarimetric observations, that
the amplitude and shape of the scattering polarization profiles of the H-alpha
line is very sensitive to the strength and structure of the chromospheric
magnetic field. The interpretation of the observations in terms of
one-dimensional radiative transfer modeling suggests that there is an abrupt
magnetization in the upper chromosphere of the quiet Sun.
