Observations of protons in the magnetosphere and magnetotail with Explorer 33

Protons in the magnetosphere and magnetotail were observed with a silicon detector on Explorer 33. Detectable fluxes of protons Ep > 0.31 Mev were measured to 10.4 RE on the sunward side of the earth and, for the first time with the present experiment, to 80 RE in the magnetotail. The small proton fluxes (≲5/cm² sec ster) measured in the magnetotail were usually anisotropic, with the largest flux apparently flowing down the tail, away from the earth. When proton bursts occurred in the tail, there was usually increased high-latitude magnetic bay activity at the earth. Durably trapped proton fluxes were observed to have intensities and spectra in agreement with previous measurements. A diurnal variation (in the L coordinate system) was observed in the 0.31- to 10-Mev trapped protons for L > 6.6 RE.