Local time asymmetries in the high-latitude boundary of the outer radiation zone for the different electron energies

Abstract

Data obtained from the Alouette II satellite are used to examine various high-latitude boundaries of the outer radiation zone as a function of local magnetic time. Four different boundaries are defined and these are referred to as the 35-keV "background" boundary, the 35-keV "smooth" boundary, the 35-keV "sharp" boundary, and the 3.9-MeV "background" boundary. All of the boundaries show a marked dependence on local magnetic time. The 35-keV "smooth" and the 3.9-MeV "background" boundaries are identified with the stable trapping region and show a 1100–2300-hour asymmetry of about 3°. The 35-keV "background" boundary falls at higher latitudes than the other boundaries at all local times; a noon–midnight asymmetry of about 6° is observed as well as a marked dawn–dusk asymmetry. The 35-keV "background" boundary is tentatively associated with the boundary of closed geomagnetic field lines and it is suggested that there is a dawn–dusk asymmetry in the field configuration. The 35-keV "sharp" boundary is identified with the inner edge of the "cusp" region and its relation to the other boundaries is examined.