Study of high-frequency EMIC wave-particle interactions in the radiation belts during the May 2024 storm using data from the PWING ground network and the Arase and POES satellites

The May 2024 storm exhibited a minimum Dst of -406 nT and was recorded as one of the largest geomagnetic storms in recent decades, causing various geomagnetic phenomena, such as the penetration of the enhanced ring current particles into the deep inner magnetosphere, the acceleration and loss of radiation belt electrons, and the generation of various plasma waves, etc. Electromagnetic ion cyclotron (EMIC) waves, also known as Pc1 geomagnetic pulsations on the ground, play an important role in the loss processes of energetic ring current protons and relativistic electrons in the radiation belts through pitch-angle scattering of those particles. In this study, we present observations of EMIC wave activity during the great geomagnetic storm of May 2024 obtained by the PWING ground-based observation network and the POES and Arase satellites. We found that the Arase satellite detected various EMIC waves, which differed depending on the storm phase. High-frequency EMIC waves with frequencies above 5 Hz were predominantly observed at L < 3 during the main and early recovery phase, suggesting that energetic particles had penetrated regions close to the Earth. POES observations revealed significant 30–80 keV proton precipitation events at L ~ 2 during the main phase in support of the ring current penetration to low L-shells. PWING ground-based observations exhibit special types of Pc1 pulsations at sub-auroral and low-latitudinal stations with frequencies higher than those of typical Pc1 waves. The variation in Pc1 wave frequency shows a relationship with the plasmapause locations and inner boundary of 33–78 keV proton fluxes. We investigate the evolution of the ring current protons and their contribution to the generation of EMIC waves during the storm. The observations provide new insights into the generation processes and evolution of EMIC waves and the inner magnetospheric dynamics during intense geomagnetic storms.