Supplementary material

Supplementary material A: Evolution of geographical maps of ROTI and S4 in the period between 16:00 UT of January 14th, 2022 to 6:00 UT of January 15th, 2022, with a time step of 5 minutes. Blue dots show the LOFAR data from all the international stations and the core station CS002. The blue shade intensity represents the S4 magnitude for the LOFAR selected frequency. If the S4 measured by a station is below the threshold of 0.05, the data is represented with a red 'x'. The yellow/black points, represents the ROTI value from GNSS above 0.2 TECU/min. Values below this threshold are indicated with a small grey dot. The red lines represent the edges of the modelled auroral oval, obtained from the closest (in time) imaging data from the DMSP satellite. Both LOFAR and GNSS data are projected at an IPP of 350 km, if outside the auroral oval, or 120 km, if inside of it. The title of each map reports the time of the ROTI data and the time of the nearest auroral oval position estimation, labelled as “Auroral time”.

Supplementary material B: Evolution of normalised power measured by the LOFAR core stations projected at an IPP of 350 km, in the period between 21:20:00 UT to 21:24:59 UT of January 14th. The grey arrow reports the direction of the velocity of the perturbation reconstructed at the nearest available time, as reported in the title. The trajectory of the entire LOFAR observations (blue line) is shown in the upper left corner, with the position at the specified time indicated by a red dot.

© R. Ghidoni et al., Published by EDP Sciences 2025