Abstract
Coronal holes (CH) are dark areas in EUV images that are generally
associated with open magnetic field regions on the Sun. They can be used
to estimate the open magnetic flux in the heliosphere by overlaying them
on magnetic field measurements. Accurately measuring the CH boundaries
over the whole Sun remains challenging due to many factors, including
limited instrument coverage, obstruction by nearby bright structures,
and the assumptions of a given detection algorithm. Here we explore the
effects of CH obscuration using a global thermodynamic MHD model of the
corona. We generate synthetic EUV images for several sets of observer
locations, and combine them into maps using current and new
obscuration-mitigating strategies. CH maps are generated from each
resulting EUV map (using an established CH detection algorithm) and used
to estimate the open flux. The importance of synchronizing the effective
EUV image height to the height of the magnetic field values is
demonstrated. Comparisons of the CH contours and open flux results with
the known open field in the simulation gives insight into how much CH
obscuration might influence observationally detected CH maps and open
flux estimates. Application of obscuration-mitigating mapping techniques
to observations is also discussed.