Estimating ground-level neutron-flux enhancements in the extreme cosmic-ray events of the next 100, 1000 and 10 000 years

• Enhancements in the cosmogenic neutron flux at ground level (GLEs) are considered.
• GLEs are deduced from data collected by nine neutron monitors over 60 years.
• The suitability of a Poisson model for fitting the occurrence of GLEs is discussed.
• The magnitude of GLEs is shown to adhere to an approximate power law.
• The occurrence and magnitude of future extreme GLEs is estimated.

Estimates are proposed of the enhancement in neutron flux which may be experienced at ground level in cosmic-ray events of extreme magnitude over the next century, millennium and ten millennia. The estimates are based on a points-over-threshold analysis of hourly neutron counts measured over the last decades by nine neutron-monitor stations located in Europe, North America and Antarctica. The present results are in good agreement with recent studies of extreme solar events based on the direct observation of flares and the abundance of cosmogenic nuclides in terrestrial and lunar archives.