Speaker
Description
The May 2024 Mother’s Day superstorm, classified as a G5-level geomagnetic event, was the strongest since November 2003. While the ionospheric response to such extreme space weather is typically monitored by conventional tools like Global Navigation Satellite System (GNSS), ionosondes, and ground-based magnetometers, this study underscores the unique and pivotal contributions that LOFAR can provide to space weather investigation.
LOFAR’s dense core stations enable detection of fine-scale ionospheric disturbances (~100 meters), while its international stations can provide a broader, mid-latitude European perspective. Moreover, the system’s dual-antenna design, comprising Low Band (LBA) and High Band (HBA) antennas, supports multi-frequency observations, offering unprecedented resolution in probing ionospheric dynamics.
During the storm’s main phase, LOFAR LBA observations revealed pronounced signal fading and absorption, correlating with the dramatic equatorward expansion of the auroral oval into mid-latitude Europe. This phenomenon, indicative of enhanced ionization and D-layer absorption at lower frequencies, was simultaneously confirmed by Total Electron Content (TEC) maps from GNSS and with observed changes in ionosonde parameters such intense and blanketing E-Region echoes, primarily occurring at virtual heights between approximately 100 and 200 km, alongside substantial deflections in local geomagnetic field components registered by magnetometers.
As the storm progressed into its recovery phase, LOFAR HBA measurements captured intense scintillation events, directly attributable to the presence of fast-moving (approaching 800 m/s), small-scale ionospheric irregularities.
The application of two different techniques for velocity reconstruction, using cross-correlation of signals from different stations and Fresnel’s frequency from single stations, enabled us to pinpoint an effective altitude of these scintillating structures, revealing the presence of uplifted ionospheric features extending beyond 1500 km. Such high-altitude phenomena were undetectable by conventional high-frequency (HF) ionosondes due to severe D-layer absorption, pervasive G-conditions, or simply altitude ranges constraints.
In addition to ionospheric disturbances, LOFAR also captured a class X 3.9 solar flare and an associated solar radio burst on the morning of May 10th. Notably, post-storm ionospheric conditions on May 12, 2024, were ideal for high-quality LOFAR observations of the redshifted H-alpha spectral line, suggesting that geomagnetic activity may help predict windows of enhanced observational quality.
In conclusion, this research represents a pioneering effort in employing LOFAR's unique observational capabilities for a comprehensive investigation of the multi-scale ionospheric response during an extreme geomagnetic superstorm. By meticulously integrating LOFAR data with established space weather datasets, we not only validate LOFAR's efficacy as a powerful instrument for ionospheric research but also highlight its distinctive advantage in resolving previously unobservable storm-time ionospheric features.
