DDTEC screens and temporal profile of LOFAR antenna RS508HBA. The lower four plots show the path-length distortions due to the ionosphere from the perspective of antenna RS508HBA during wild and calm periods. Middle row: inferred DDTEC screen, and the bottom row shows the measured DDTEC screen. The black star indicates the reference direction, hence the DDTEC is always zero in that direction. The top plot shows the DDTEC for a single direction over the course of the observation, and it clearly shows that the temporal behaviour changed around 3.5 h into the observation.