Observations of ions with nuclear charge Z ≧9 in the inner magnetosphere

Abstract

Ions heavier than protons, such as helium ions and CNO ions, are known to exhibit substantially enhanced trapped fluxes at MeV energies in the interior of the earth's radiation belts associated with some, but not all, magnetic storms. In this report we extend the Explorer 45 heavy ion data analysis to ions heavier than fluorine, i.e., ions with nuclear charge Z ≳9 during and following a major magnetic storm on August 4, 1972. Our heavy ion detector telescope does not permit a precise identification of these ions; but if they are magnesium ions (say), then an equatorially mirroring peak trapped flux of 0.02 ions/(cm² s sr keV) is derived on L shells just below L =3 at energies 12.8–51.2 MeV per ion (533–2133 keV per nucleon). Other possible ion contributions include silicon and iron. The fluxes of these ions are found to decay on time scales typically several tens of days; this is substantially faster than that of helium ions and somewhat faster than that of oxygen ions in the lower MeV range. We infer that the pitch angle distributions of the Z ≳9 ions were quite anisotropic over a range of L shells with the exponent m in the relation jLOC=jEQ sinm αEQ having a value of at least 10; this value is arrived at from two independent techniques.