Authors: Zhenguang Huang (University of Michigan), Gábor Tóth (University of Michigan), Jia Huang(University of California), Nishtha Sachdeva (University of Michigan), Bart van der Holst (Boston University), and Ward B. Manchester (University of Michigan)

The size of coronal hole greatly depends on the source surface height when a potential field source surface (PFSS) model is applied. A PFSS model applies the current-free approximation, and the source surface height is the surface beyond which the magnetic field is entirely radial. 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 magnetohydrodynamic model, in our case the Alfvén 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 showed that the open field area (corona hole) is comparable to the AWSoM solution when the adjusted source surface is applied. 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.