The Carrington event: Possible solar proton intensity–time profile

A possible >30 MeV solar proton intensity–time profile associated with the Carrington solar flare event of 1 September 1859 is constructed. The derived profile is consistent with a >30 MeV proton omni-directional fluence of 1.9 × 1010 cm−2 found by the analysis of solar proton generated NOy radicals that are deposited in polar ice. The intensity–time profile of the solar particle flux is constructed by assuming that the Carrington solar event is part of the class of interplanetary shock-dominated events where the maximum particle flux is observed as the shock passes the Earth. This assumption is based on the knowledge that the very large solar proton fluence events (those with >30 MeV omni-directional fluence exceeding 1.0 × 109 cm−2) associated with central meridian solar activity during the last 50 years belong to this class of event. The absence of a statistically significant increase in the observed concentration of the cosmogenic nuclide 10Be for 1859 indicates that the solar cosmic radiation produced in the Carrington event had a soft spectrum, similar to other interplanetary shock-dominated events.