  A potential field solution is widely used to extrapolate the coronal magnetic
field above the Sun's surface to a certain height. This model applies the
current-free approximation and assumes that the magnetic field is entirely
radial beyond the source surface height, which is defined as the radial
distance from the center of the Sun. Even though the source surface is commonly
specified at 2.5 Rs (solar radii), previous studies have suggested that this
value is not optimal in all cases. In this study, we propose a novel approach
to specify the source surface height, by comparing the areas of the open
magnetic field regions from the potential field solution with predictions made
by a magnetohydrodynamics model, in our case the Alfven Wave Solar atmosphere
Model. We find that the adjusted source surface height is significantly less
than 2.5 Rs near solar minimum, and slightly larger than 2.5 Rs near solar
maximum. We also report that the adjusted source surface height can provide a
better open flux agreement with the observations near the solar minimum, while
the comparison near the solar maximum is slightly worse.
