Short-term Evolution of Coronal Hole Boundaries

Abstract

The interaction of open and closed field lines at coronal hole (CH) 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 CH boundary displacements on short timescales. The boundary displacements were found to be isotropic and to have typical expansion/contraction speeds of <=2 km s^-1, which indicate magnetic reconnection rates of <=3 × 10^-3. The observed displacements were used in conjunction with the interchange reconnection model to derive typical diffusion coefficients of <=3 × 10¹³ cm² s^-1. These results are consistent with an interchange reconnection process in the low corona driven by the random granular motions of open and closed fields in the photosphere.