Features of Ground Level Enhancement (GLE #74) Event on 11 May 2024

Abstract

Ground Level Enhancement (GLE #74) occurred on 11 May 2024 following an X5.8 solar flare from active region AR 13668 and the associated halo coronal mass ejection. The event was observed by both ground‐based neutron monitors (NMs) and space‐borne instruments and occurred during a deep Forbush decrease and one of the strongest geomagnetic storms of the current solar cycle, making its analysis particularly challenging. Using de‐trended NM observations and explicitly accounting for storm‐time variations in geomagnetic cutoff rigidity, we reconstructed the temporal evolution of the rigidity spectra and pitch‐angle distributions of solar energetic particles (SEPs). The SEP rigidity spectra were moderately hard during the onset phase and exhibited a pronounced roll‐off that gradually weakened as the event evolved, resulting in progressively softer spectra. The particle angular distribution revealed a significant anti‐Sunward component and was best represented by a double‐Gaussian pitch‐angle distribution, suggesting complex interplanetary transport associated with disturbed magnetic field structures. The reconstructed SEP characteristics were in good overall agreement with GOES observations. These results provide new constraints on the acceleration and transport of high‐energy SEPs during extreme space‐weather events and demonstrate the robustness of NM‐based SEP reconstructions under highly disturbed geomagnetic conditions.