  The measurement of solar magnetic fields using the Zeeman effect diagnostics
has a fundamental 180 degree ambiguity in the determination of the azimuth
angle of the transverse field component. There are several methods that are
used in the community and each one has its merits and demerits. Here we present
a disambiguation idea that is based on the assumption that most of the magnetic
field on the sun is predominantly vertical. While the method is not applicable
to penumbra or other features harboring predominantly horizontal fields like
the sheared neutral lines, it is useful for regions where fields are
predominantly vertical like network and plage areas. The method is tested with
the full-disk solar vector magnetograms observed by the VSM/SOLIS instrument.
We find that statistically about 60-85 % of the pixels in a typical full-disk
magnetogram has field inclination in the range of 0-30 degrees with respect to
the local solar normal, and thus can be successfully disambiguated by the
proposed method. Due to its non-iterative nature, the present method is
extremely fast and therefore can be used as a good initial guess for iterative
schemes like nonpotential field computation (NPFC) method. Furthermore, the
method is insensitive to noisy pixels as it does not depend upon the
neighboring pixels or derivatives.
