Spatial distribution of energetic particles in the distant magnetotail

Abstract

The spatial distribution of energetic particles in the distant magnetotail is examined by using identical sets of two complementary energetic particle experiments aboard the IMP 7 and 8 spacecraft. The combined IMP 7 and 8 data set provides nearly 10 years of satellite observation. The quantitative distributions of energetic electrons in two energy ranges (30 keV ≤Ee ≤100 keV, 220 keV ≤Ee ≤2.5 MeV) and energetic protons (50 keV ≤Ep ≤220 keV, 290 keV ≤Ep ≤500 keV) are presented in terms of occurrence frequency and the average particle flux intensity over an 80 RE × 70 RE plane perpendicular to the sun‐earth line. The θ‐shaped particle distribution over the solar magnetospheric YZ plane in the antisolar direction is clearly demonstrated at all energies and for both species. The ‘O’ part of the θ corresponds to the magnetosheath region, and the cross bar is the average plasma sheet configuration. A distinct, species dependent, dawn‐dusk asymmetry in particle distribution is observed in the plasma sheet and to a lesser extent also in the magnetosheath. Energetic electrons are observed most often in the morningside of the plasma sheet and protons in the evening side. The degree of asymmetry differs for electrons and protons and is energy dependent. Geomagnetic activity affects the particle distribution substantially. At high geomagnetic activity, the occurrence frequency increases by about a factor of 2 and the average flux intensity is enhanced by approximately one order of magnitude.