Loss and replenishment of electrons in the inner radiation zone during 1965-1967

Abstract

The loss and replenishment of electrons (E>0.3 Mev and E>0.5 Mev) in the inner zone were studied during 1965, 1966, and 1967 by electron spectrometers on the Pegasus A and B spacecrafts. Several featuers were apparent from the data: (a) The magnitude of the trapped flux and its decay time are related to the state of solar activity. (b) Large increases in flux follow large magnetic storms. The fractional increase is largest at high L values (L=2.0) and is observable below L=1.25. (c) The rise time of the flux increase is shortest at high L, and the decay times after storms are complex. (d) The increased flux is accompanied by a softening of the electron spectrum between 300 and 500 kev. (e) The increase in the flux of trapped electrons at L=1.8–2.2 is accompanied by a large flux of precipitating electrons observed within the loss cone. (f) The precipitating flux decreases with decreasing L; it is also highly variable, usually ranging within one day from background to 106 electrons/cm2 sec. (g) The precipitated flux e-folding energy is 41±3 kev, roughly similar to the e-folding energy of the trapped flux at L=1.8–2.2. (h) The precipitation period and maximum precipitated flux depend not only on the magnitude of magnetic activity index, Ap, but also on the length of time the activity continues. We conclude that the exponential decay time of the inner radiation zone is a variable, dependent on the interval of time over which the decay is measured. We suggest that the source of the precipitated electrons at L=2 and of the increased electron flux observed at L=1.25 is the same. The evidence for this suggestion is the similarity in behavior of the trapped and precipitated flux with magnetic activity, the similarity of the e-folding energy between the trapped and precipitated flux at L=2, and the softening of the spectrum associated with the observed flux increases at the low L values.