Research Article

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

¹ Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, 00143 Rome, Italy
² Physics and Astronomy Department “Augusto Righi”, University of Bologna, Via Zamboni 33, 40126 Bologna, Italy
³ SpacEarth Technology, Viale dell’Astronomia 18, 00144 Rome, Italy
⁴ Space Environment and Radio Engineering (SERENE) research group, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK
⁵ ASTRON – The Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
⁶ Space Radio-Diagnostics Research Centre, University of Warmia and Mazury, ul. Romana Prawochenskiego 9, 10-719 Olsztyn, Poland
⁷ Center for Solar-Terrestrial Research, New Jersey Institute of Technology, Newark, NJ 07102, USA
⁸ Department of Electronic and Electrical Engineering, University of Bath, Claverton Down, Bath, BA2 7AY, UK
⁹ Centrum Badań Kosmicznych Polskiej Akademii Nauk, Bartycka 18 A, 00-716 Warsaw, Poland
¹⁰ Riga Technical University, 6A Kipsalas Street, Rīga, LV-1048, Latvia
¹¹ Ventspils University of Applied Sciences, Engineering Research Institute “Ventspils International Radio Astronomy Center”, Ventspils, LV-3601, Latvia

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 23 May 2025
Accepted: 18 December 2025

Abstract

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.