Reconstruction of the fluence of extreme solar particle events registered in cosmogenic proxies

Extreme solar particle events (ESPEs) are infrequent yet highly potent manifestations of solar activity. These events result in the production of significant amounts of cosmogenic isotopes(CIs): 10Be, 36Cl, and 14C, which are subsequently deposited in natural stratified archives. Analyzing CI measurements from these archives allows us to assess the particle fluxes during ESPEs. In this study, we introduce a novel approach to reconstruct ESPE fluence (integral flux) by using recent modelling advancements. This method enables the integration of diverse CI data within a single comprehensive model. Within the new approach, ESPE fluence is represented as an ensemble of scaled fluence reconstructions for ground-level enhancement (GLE) events, detected by the neutron monitor network since 1956 and coupled with satellite and ionospheric measurements. The reconstructed ESPE fluences exhibit a softer spectral shape compared to previous estimates, leading to significantly higher estimates of the low-energy (E <100 MeV) fluence. Consequently, ESPEs pose an even greater risk to modern technological systems than previously believed. To facilitate broader applications, the reconstructed ESPE fluences are fitted using a modified Band function which simplifies the utilization of the obtained results in various practical contexts.