Model description:

The coronal and heliospheric magnetic field model 
(the Horizontal Current, Current Sheet and Source Surface, HCCSSS or CSSS, model)
separates the solar atmosphere into three layers using two spherical surfaces:
one is called the cusp surface and located at r=Rsp~2.5 Rs, near cusp points
of helmet streamers; and the other is called the source surface and located 
at r=Rss~15 Rs, near the Alfven critical point where ALL solar wind do
propagate radially, as defined for the source surface.

In the lowest layer below the cusp surface (r < Rsp), closed field lines 
are expanded using a free parameter $a$ that characterizes the height of
horizontal currents and mimics the effect of the outward propagating 
solar wind on the magnetic field there. The effect is similar to the effect
caused by the source surface of r=2.5 Rs used in the PFSS model. The effect
of the heliospheric current sheet on the magnetic field between Rsp and Rss
are estimated using Schatten's approach (1971). Beyoned the source surface,
the magnetic field can be mapped to 1 AU using the Parker model.   

This model is more relistic in physics than the PFSS model, and the predicted
magnetic field beyond cusp points is better than the PFSS model as follows,
(1) The magnetic field at the cusp surface of Rcp ~ 2.5 Rs are open but not
    radial everywhere, consistent with white light observations of the corona.
(2) The magnetic field beyond the cusp surface, Rcp < r <= Rss, changes from
    non-radial to radial
(3) The field on the source surface of Rss~15 Rs are radial everywhere, 
    consistent with the real solar wind around the Alfven critical point.

This model may be used to model observed non-radial helmet streamers and the
observed radial variation of coronal helmet streamer belts, and to predict the
uniformly distributed radial component of the heliospheric magnetic field
observed by Ulysses. Therefore, the coronal and heliospheric magnetic field
from the solar surface to 1 AU obtained using this model may be used as the 
initial condition for the coronal and heliospheric MHD models of CMEs.

Required input:

The various Carrington synoptic maps as a proxy of the whole surface 
distribution of the observed photospheric magnetic field, and 
the free parameters, $a$, Rsp, Rss and Nmax, the order number of the
spherical harmonic coefficients.

Expected outpot:
The three components of the magnetic field between 1 Rs and 1 AU, and
the field lines in the steady state of the solar corona and solar wind.