Summary: April 22, 2010
Coronal hole boundaries evolution at small scales: II. XRT view
Can small-scale outflows at CHBs be a source of the slow solar wind?
S. Subramanian, M. S. Madjarska and J. G. Doyle
Armagh Observatory, College Hill, Armagh BT61 9DG, N. Ireland
Received date, accepted date
Aims. We aim to further explore the small-scale evolution of coronal hole boundaries using X-ray high-resolution and high-cadence
images. We intend to determine the fine structure and dynamics of the events causing the changes of the coronal hole boundaries and
to explore the possibility that these events are the source of the slow solar wind.
Methods. We developed an automated procedure for the identification of transient brightenings in images from the X-ray telescope
on-board Hinode taken with an Al Poly filter in the equatorial coronal holes, polar coronal holes, and the quiet Sun with and without
transient coronal holes.
Results. We found that in comparison to the quiet Sun, the boundaries of coronal holes are abundant with brightening events including
areas inside the coronal holes where closed magnetic field structures are present. The visual analysis of these brightenings revealed
that around 70% of them in equatorial, polar and transient coronal holes and their boundaries show expanding loop structures and/or
collimated outflows. In the quiet Sun only 30% of the brightenings show flows with most of them appearing to be contained in the
solar corona by closed magnetic field lines. This strongly suggests that magnetic reconnection of co-spatial open and closed magnetic
field lines creates the necessary conditions for plasma outflows to large distances. The ejected plasma always originates from pre-
existing or newly emerging (at X-ray temperatures) bright points.