Ionospheric response to the January 2022 geomagnetic storm using LOFAR and GNSS

We investigate the dynamics of the multi-scale processes involved in the ionospheric response to a geomagnetic storm that occurred on January 14th-15th, 2022. During this storm, the LOw Frequency ARray (LOFAR), a European distributed radio telescope array, provided ionospheric measurements from the radio source Cassiopeia A that we complemented with the ionospheric information provided by the Global Navigation Satellite System (GNSS) receivers covering the European sector. LOFAR operates in the HF/VHF band (between 30 and 250 MHz), while GNSS signals are in the L-band (similar to 1 GHz), translating into the possibility to investigate the ionospheric irregularities formed in response to the storm at different spatial scales. The combined use of data from these two instruments allowed us to observe three distinct phenomena: (i) the increment of direct particle precipitation in the auroral oval, (ii) the steepening of the equator-ward edge of the ionospheric trough, and (iii) the propagation toward lower latitudes of wave-like structures having scale sizes of a few kilometres and a velocity of hundreds of meters per second.