Comment on the use of solar proton spectra in solar proton dose calculations

The high energy solar particle event of 29 September 1989 has been used to evaluate the solar proton spectral characteristics throughout the event. The results show that the solar cosmic ray spectrum is extremely hard at low energies with the magnitude of the slope increasing with increasing energy and with time. This spectral evolution, when used for the events of the 19th solar cycle before routine spacecraft measurements were available, results in a decrease in the earlier estimates of radiation dose during these high-energy solar proton events.