Path of the 154 MHz radio source. (a): Line-of-sight-integrated DEM map. The white-to-blue points show the time evolution of the 154 MHz radio source in 10 s intervals. The velocities of the points in Phase 1 and Phase 2, obtained from 0.25 s data, are indicated by the labelled arrows. (b): Combination of an AIA 193 Å image during the event with a PFSS extrapolation. The radio emission clearly moves around a higher Alfvén speed region, favouring lower magnetic field strength regions.