Variations of the trapped particle population and of cutoff and pitch angle distribution of simultaneously observed magnetospheric solar protons during substorm activity

Abstract

The behavior of solar protons (1.5–2.7 MeV) and trapped electrons (>1.5 MeV) observed by a low-altitude polar-orbiting satellite (Azur) during the occurrence of an isolated substorm (March 29–30, 1970) is examined. Onset of the substorm is determined and its development is discussed by using energetic and high-energy particle data from the ATS 5 satellite. The comparison of equatorial and low-altitude electron data shows that the behavior of the trapped electron population is consistent with the adiabatic model given by Lezniak and Winckler (1970). Observation of an isotropic pitch angle distribution of the solar protons leads to the conclusion that there is evidence for strong pitch angle scattering of these particles in the pseudotrapping region. We also observed during the substorm a large change in the slope of the solar particle flux profile at cutoff that occurred simultaneously with a variation of the trapping boundary. It is suggested that this effect might explain the often observed ‘deep entry’ of solar protons into closed drift shells well below the nominal cutoff.