Solar energetic particle ion composition of AR 13664 during the May 2024 great solar storm

During mid-May 2024, active region (AR) 13664 produced a series of M- and X-class flares along with several coronal mass ejections (CMEs) which resulted in exceptionally strong aurora at Earth. This study presents in-situ solar energetic particle (SEP) ion composition data from STEREO-A, ACE and Parker Solar Probe (PSP) as their connectivity to AR 13664 varied throughout the great solar storm period.

 

The observational period was between 08 to 20 May, STEREO-A was 12° longitudinally separated from ACE at 0.96 AU and the SEP intensities rose gradually as a result of several CMEs from AR 13664. Notable events for the spacecraft near Earth included a magnetic field strength jump to 88 nT and the appearance of aurora on Earth on 10 May. Additionally, on 13 May an M6 flare was followed by another SEP event with rapid onset and an estimated particle path length of 0.97 +/- 0.16 AU.

 

PSP, set at approximately 95° longitudinal separation from Earth, was at 0.74 AU during the observational period. PSP measured a qualitatively similar gradually rising SEP intensities beginning on 11 May and continuing until the magnetic field strength rapidly increased to 100+ nT on 16 May coincident with a jump in SEP intensity. Finally, on 20 May an X16 flare from AR 13664 produced an Fe-rich SEP event.

 

Throughout the observational period, AR 13664 produced flares and CMEs causing SEP events with Fe/O ratios that varied from <0.01 to 0.8+ at each spacecraft’s location. The difference in composition for STEREO-A and ACE, during the early part of the observational period, suggests longitudinally narrow SEP events or highly varying magnetic connectivity. Yet, on 20 May the X16 flare coincided with Fe/O-rich composition for all three spacecraft despite over 100° of longitudinal separation.