Links between magnetic fields and plasma flows in a coronal hole
We compare the small-scale features visible in the Ne VIII Doppler-shift map of an equatorial coronal hole as observed by SUMER with the small-scale structures of the magnetic field as constructed from a simultaneous photospheric magnetogram by a potential magnetic-field extrapolation. The left figure shows closed magnetic loops (yellow)and the right figure open field lines (red-brown). The black line outlines the boundary of the coronal hole and the red box marks the field of view of SUMER. We find that long closed loops are absent in the coronal hole, but present just outside (close to the upper right edge) in the quiet Sun.
See original letter by Wiegelmann, Xia and Marsch in A&A for additional information.
We project the extrapolated magnetic field lines (closed in yellow, open in red-brown) onto a map of the Doppler shift of the Ne VIII (77 nm) emission line. A blue shift corresponds to and outflow of the plasma and red shift to inflow. In white patches the plasma is at rest. We find that the coronal magnetic field is a key player in constraining plasma flow and guiding the nascent solar wind outflow. We find the largest blue shifts (outflow) with speeds up to 20 km/s (darkest blue patches) are associated with those regions where intense open fields of uniform polarity are concentrated. In contrast, the plasma confined in small loops in the coronal hole does not reveal any significant flow.