  The morphology of spectral line polarization is the most valuable observable
to investigate the magnetic and dynamic solar atmosphere. However, in order to
develop solar diagnosis, it is fundamental to understand the different kinds of
anomalous solar signals that have been routinely found in linear and circular
polarization (LP,CP). The goal of this paper has been to explain and
characterize the morphology of solar CP signals by understanding the combined
effect of magnetic fields, velocity gradients, and atomic orientation in
general NLTE regime. To that aim, an analytical two-layer model of the
polarized radiative transfer equation is developed and used to solve the NLTE
problem with atomic polarization in a semi-parametric way. The formation of
polarization is thus insightfully described with certain precision without
resorting in MHD models or sacrifying key physical ingredients. The potential
of the model for reproducing solar anomalous CP is shown with detailed
calculations. The essential physical behavior of dichroism and atomic
orientation is described, introducing the concepts of dichroic inversion,
neutral and reinforcing medium, critic intensity spectrum, and critic source
function. It is shown that the zero-crossings of the CP spectrum are useful to
classify its morphology and understand its formation. This led to identify and
explain the morphology of the seven most characteristics CP signals that a
single (depth-resolved) scattering layer can produce. Futhermore, it is found
that a minimal number of two magnetic layers along the LOS is required to fully
explain anomalous solar CP signals, and that the morphology and polarity of
Stokes V depends on magnetic, radiative and atomic polarities. Some
implications of these results are presented through a preliminar modeling of
anomalous CP signals in the Na I D and Fe I 1564.8 nm lines.
