Outer Zone Protons

Abstract

Charged particle detectors aboard satellites Explorer XII, XIV and XV have provided measurements of the intensity and spectra of 100 keV to 1700 keV protons in the region above two earth radii during 1961 and 1962. These results as well as those of other measurements are summarized.

Additional measurements made on Explorer XXVI in February 1965 are presented and compared with the previous results. They show that: (1) between December 1962 and February 1965 the intensities of protons having energies greater than 500 keV increased by a factor of two or more over most and possibly all of the region from 2.5 to 5 earth radii, and (2) over the same region the 100 keV to 300 keV protons are greatly depleted in 1965.

During a magnetic storm on 18 April 1965 and while Explorer XXVI was near apogee (5 earth radii) with L almost constant, the low energy protons were observed to increase dramatically over a ten minute period. During the same period the 10 keV to 100 keV electrons decreased in intensity and then over the next 30 minutes built back up with higher average energy. Two such events were observed, both coincident with high latitude negative bays. The results indicate that the > 100 keV protons are not directly related to the ring current particles.