Searching for a Boundary Layer as a Source of the Slow Solar Wind

Recent investigations in the solar wind plasma and magnetic field characteristics indicate a likely existence of a "boundary layer" where the slow solar wind originates from. Such a boundary layer resides at the coronal hole boundary where the open field lines emanating from it expand super-radially into the corona. We select two adjacent coronal holes that are the sources of two consecutive solar wind streams measured by ACE. One is a low-latitude extension of the north polar coronal hole that past the central meridian on August 18, 2015, and the other is an equatorial coronal hole that past the central meridian on August 20. We use data from SDO/AIA, SDO/HMI and Hinode/EIS in combination with PFSS and 3D MHD models to investigate the evolution of the coronal and magnetic field properties at the boundary of these coronal holes and search for signatures of such a boundary layer.