Observations of proton bursts in the magnetotail with Explorer 35

Energetic proton bursts (Ep≥0.32 Mev) are observed at 60 RE in the magnetotail by Explorer 35. The intensity is usually anisotropic. The net proton flow as measured in the ecliptic plane is found to be most often, but not always, nearly parallel or antiparallel to the local magnetic field and is sometimes toward and sometimes away from the earth. Companion observations outside the bow shock by Explorer 33 show that the proton bursts are not of solar origin. One observation evidences possible proton flow away from the earth, across the neutral sheet, and back toward the earth parallel to the field in the ecliptic plane. The proton bursts have spectral e-folding energies of 50–110 kev and peak intensities of 14–420 (cm² sec ster)−1, values that are similar to those for protons near the outer-zone trapping boundary.