Short-term evolution of coronal hole boundaries

The interaction of open and closed field lines at coronal hole boundaries is widely accepted to be due to interchange magnetic reconnection. To date, it is unclear how the boundaries vary on short timescales and at what velocity this occurs. Here, we describe an automated boundary tracking method used to determine coronal hole boundary displacements on short timescales. The bound- ary displacements were found to be isotropic and to have typical expansion/contraction speeds of \leq2 km s^-1, which indicate magnetic reconnection rates of \leq 3 \times 10^-3. The observed displacements were used in conjunction with the interchange reconnection model to derive typical diffusion coeffi- cients of \leq 3 \times 10^13 cm^2 s^-1. These results are consistent with an interchange reconnection process in the low corona driven by the random granular motion of open and closed fields in the photosphere.