LOFAR uniqueness under extreme ionospheric conditions: The May 2024 Mother’s Day superstorm

The May 2024 Mother’s Day superstorm, the strongest since November 2003, triggered significant ionospheric disturbances. Indeed, during the superstorm, the ionosphere above Europe was transformed into a severely depleted, super-high-altitude plasma structure extending beyond 1500 km above Earth’s surface. We highlight the unique contributions of the LOw Frequency ARray (LOFAR) to ionospheric weather research on this extreme event. Originally designed for radio astronomy, LOFAR’s extensive European network of 52 stations and wide-band capabilities enable high-resolution ionospheric monitoring at both local and regional scales. Leveraging LOFAR measurements, we characterise a plethora of ionospheric effects that occurred during the main and early recovery phases of the storm. We did this by observing significant signal fading associated with the equatorward expansion of the auroral oval during the main phase and by capturing high-speed moving ionospheric irregularities (up to ~800 m/s), and quantifying extreme ionospheric uplift (up to 1500 km) under conditions where conventional HF instruments were not usable due to the occurrence of D-layer absorption, ionospheric G-conditions and uplift above ionosonde altitude range. In this investigation, we harness the unique capabilities of LOFAR to direct view into the structure and dynamics of the ionosphere under the most extreme space weather conditions. Our results confirm LOFAR as an insightful instrument for ionospheric research, offering critical capabilities for advancing storm impact assessment, forecasting, and mitigation strategies.