Catalogue and statistics of greater than 100 MeV solar proton events during solar cycles 23-25 from SOHO-ERNE observations

Abstract

The SPEARHEAD (specification, analysis, and re-calibration of high-energy particle data) project, funded by the European Union Horizon Europe programme, enhances the accuracy and usability of high-energy particle measurements. It investigates particle acceleration, release, and transport during solar eruptions by refining instrument response functions and cross-calibrating datasets. We present a comprehensive catalogue of greater than 100 MeV proton events identified from May 1996 to August 2024 using SOHO-ERNE penetrating-particle rates, together with associated solar phenomena derived from multi-instrument observations. The SEP events were detected through a systematic scan of ERNE-HED counter data and cross-calibrated with SOHO-EPHIN to derive peak fluxes and fluences. Each event was associated with its likely parent eruption using X-ray (XR) (GOES-XRS, RHESSI, SolO-STIX), radio (Wind-WAVES, STEREO-WAVES, ground-based observatories), and gamma-ray (Fermi-LAT) observations, CMEs (SOHO-LASCO), and ground-level enhancements (GLEs) (neutron monitors). Timings and physical properties were systematically compared to investigate the relationships between SEP onset, flare evolution, CME kinematics, and radio signatures. Statistical analyses reveal that most SEP releases closely follow flare and CME onsets, with moderate SEP-XR-CME correlations, and a strong SEP-GLE fluence link. These results indicate that high-energy SEP events are typically associated with strong solar activity signatures, with the observed intensities and timings strongly modulated by magnetic connectivity and coronal conditions. This catalogue provides the most extensive reference to date for high-energy SEP events over solar cycles 23-25, establishing a unified framework for future investigations of extreme particle acceleration.

Figures (26)

• Figure 1: Temporal distribution of the $>$100 MeV proton events included in the catalogue (histogram). Red dots show the corresponding peak proton intensities ($I_\mathrm{p}$) with uncertainties measured by SOHO/EPHIN, plotted against the secondary (right-hand) axis.
• Figure 2: Distributions of $>$100 MeV proton peak intensities (panel (a)) and fluences (panel (b)) measured by SOHO/EPHIN for 107 and 97 events of the catalogue, respectively.
• Figure 3: Representative example of the solar associations for the 28 October 2021 $>$100 MeV SEP event (No 137) corresponding to GLE73. Panel (a): ERNE proton counts at $>$100 MeV. Panel (b): Soft X-ray flux (1–8 Å, GOES, blue) and high-energy flare emissions, including hard X-rays (Solar Orbiter/STIX, 4–10 keV, purple) and $\gamma$-rays (Fermi/LAT, $>$100 MeV flux, pink). Panel (c): Radio dynamic spectrum (e.g. Wind/WAVES) with over-plotted CME height–time profile from coronagraph observations (SOHO/LASCO). Panel (d): Ground-level neutron monitor data showing relativistic particle increases.
• Figure 4: Statistics of the identified soft X-ray flares associated with $>$100 MeV SEP events (131/172, 76%). From left to right: SXR peak flux, flare longitude in Stonyhurst co-ordinates, rise time (peak minus start time), and total duration.
• Figure 5: Statistics of the identified hard X-ray flaring sources for the $>$100 MeV catalogue (76%, 131/172 events). From left to right: distribution of HXR peak intensity, flare fluence (in counts), rise time (HXR peak -- start), and total duration.