STRUCTURE AND PROPERTIES OF THE SUBSOLAR MAGNETOPAUSE FOR NORTHWARD INTERPLANETARY MAGNETIC-FIELD - MULTIPLE-INSTRUMENT PARTICLE OBSERVATIONS

The structure and properties of the subsolar magnetopause for northward interplanetary magnetic field (IMF) are studied with measurements from 10 different instruments for three ISEE crossings. Data show that the overall structure and properties are similar for the three crossings, indicating the magnetopause is relatively well determined in the subsolar region for strongly northward IMF. The measurements from different instruments are consistent with each other and complementary based on the current knowledge of space plasma physics. The combined data set suggests that the magnetopause region is best organized by defining a sheath transition layer and steplike boundary layers. The sheath transition layer contains mostly magnetosheath particles. The magnetosheath, magnetospheric, and ionospheric populations are mixed in the interior boundary layers. This result, which is consistent with previous studies, is now supported by observations of a much broader spectrum of measurements including three-dimensional electron, energetic particle, heavy ion and plasma wave. Some new features are also found: even for quiet subsolar magnetopause crossings, transient or small-scale structures still occur sporadically; slight heating may occur in the boundary layers. Some outstanding issues are clarified by this study: the electron flux enhancements in the lowest energies in the boundary layers and magnetosphere are ionospheric electrons and not photoelectrons from the spacecraft; for northward IMF, they are photoelectrons, but for southward IMF they may be secondary electrons; and the density measurements from differential and integral techniques are similar, leaving no room for a significant ''invisible'' population.