Proton energy distributions from 0.060 to 3.3 Mev at 6.6 Earth radii

Proton differential fluxes are reported for 12 energies from 0.060 to 3.3 Mev at 6.6 earth radii for the time period of October 2 to 13, 1968. The proton energies were measured with a surface barrier semiconductor detector and a stacked discriminator pulse height analyzer on the Air Force Office of Aerospace Research Satellite OV2-5 (1968-81A). The typical quiettime fluxes decreased by 8 orders of magnitude over the measured energy interval. During this time the energy spectrum varied from E−3.5 to E−6.0. Below 200 kev the energy distributions flatten but never peak above the energy of the lowest channel, 68 kev. Energy spectra associated with the two magnetic storms on October 2 and 12 are presented. After the storms the fluxes were higher than before; this is particularly true at the lower energies measured. Quiettime pitch angle distributions near the local noon-midnight meridian clearly show the east-west effect caused by the radial gradient in the fluxes. The pitch angle distributions at local midnight show the ‘drift loss cone’ predicted by Roederer. This experiment provides the first confirmation of the Roederer [1967] model of shell splitting in the earth's magnetic field by measured proton angular distributions.