Quiet time mass composition at near‐geosynchronous altitudes

Abstract

Mass composition data acquired from the near‐geosynchronous SCATHA spacecraft during magnetically quiet times are analyzed. The time intervals over which data were included in the study span some 4 months in the spring and summer of 1979. This allows a reasonable coverage in both L shell and magnetic local time. At the higher L shells, L > 6.5, the mass composition data are consistent with sunward convection of plasma sheet particles. Protons and alpha particle fluxes peak near 90° pitch angle. There is evidence that the alpha particle spatial distribution has a sharp inner edge near L = 6.5. At lower L values, the proton characteristics change. The density of protons above 1 keV decreases, while the lower‐energy protons show an increase in density. The oxygen ions show a similar change, in that there is a large increase in the lower‐energy oxygen ions from high L to low L, especially in the dusk and midnight local time sectors. This suggests that the ionosphere may be continuously supplying plasma to the inner magnetosphere even during magnetically quiet times.