Panel a: time-distance plots demonstrating the apparent plane-of-sky motion of brightening in the 171 Å channel along slice A (top panel) and slice B (bottom panel), which are shown in Fig. 2. The horizontal dotted line denotes the location of the apparent coronal 3D null point, and vertical dashed lines correspond to the three time intervals used to produce the three panels in Fig. 2. Panel b: time-distance plots for the 193 Å channel. Overlaid on both time-distance plots are dash-dotted lines indicating approximate velocities of the flow features from which they are offset. Panel c: NRH brightness temperature, averaged over the area within a 50% contour of each NRH image, for its 7 highest recorded frequencies, smoothed over 6 points, and normalised to clarify local peaks. Panel d: NRH extent, measured as the linear distance between the centroid of the highest and lowest frequency stable sources, which were 432 and 298 MHz, respectively.