GEOMAGNETICALLY TRAPPED ANOMALOUS COSMIC-RAYS

Since its launch in July 1992, the polar-orbiting satellite SAMPEX has been collecting data on geomagnetically trapped heavy ions, predomina ntly O. N, and Ne, at energies greater than or similar to 15 MeV/nucle on and in a narrow L shell range near L = 2. Their location, elemental composition, energy spectra, pitch angle distribution, and time varia tions all support the theory that these particles originated as singly ionized interplanetary anomalous cosmic rays that were stripped of el ectrons in the Earth's upper atmosphere and subsequently, trapped, The O are observed primarily at pitch angles outside the atmospheric loss cones, consistent with a trapped population, and their distribution t here is nearly isotropic. The abundances relative to O of the N, possi bly Ne, and especially C are lower than the corresponding interplaneta ry values, which may be indicative of the trapping efficiencies. The d istributions of trapped N, O, and Ne in energy and L shell suggest tha t most of the ions observed at the SAMPEX altitude of similar to 600 k m are not fully stripped when initially trapped. A comparison of the t rapped intensity with the much lower interplanetary intensity of anoma lous cosmic rays provides model-dependent estimates of the product of the trapping probability and the average trapped particle lifetime aga inst ionization losse's in the residual atmosphere for particles that mirror near the SAMPEX altitude.