Evolution of the LOS magnetic field underlying the coronal hole at a cadence of 14 h. A subregion is highlighted to show the motion of a long-lived unipolar magnetic element (blue contour). The coronal hole boundary derived from EUV observations is shown in red. The green contour in panel a gives the location of a coronal bright point within the coronal hole (which can be seen in 193 Å), which no longer exists 14 h later.