Solar proton event of February 5, 1965

Solar protons reached the vicinity of the earth after the class 2 solar flare of February 5, 1965, and were measured from satellite 1964-45A. Four hours after the flare the integral fluxes above 10 Mev, 20 Mev, 40 Mev, and 80 Mev were, respectively, 350, 250, 100, and 5 protons/cm2 sec. These fluxes decayed with time constants ranging from 16.8 hours for the lowest energy threshold to 4 hours for the highest energy threshold. Changes in the fluxes by a factor of ≈3 that ocurred within a time of minutes were also observed.