Birkeland currents and charged particles in the high‐latitude prenoon region: A new interpretation

Abstract

Simultaneous, conjugate measurements of magnetic fields and charged particles at low altitude in the high‐latitude prenoon sector and the magnetosheath were made with the DMSP F7, HILAT, and Active Magnetospheric Particle Tracer Explorers (AMPTE) CCE satellites on November 1, 1984. These data show that the low‐latitude portion of the traditional “cusp” particle signature is coincident with the prenoon region 1 current system in both hemispheres and for both northward and southward interplanetary magnetic fields (IMF). The traditional “cusp” Birkeland currents are associated with the dispersion region of cusp ions when the IMF is directed southward and with electron fluxes that are slightly enhanced over polar rain intensities. Finally, electron spectra measured by AMPTE CCE in the magnetosheath near 1000 MLT are similar in shape and energy to those acquired at low altitude by both DMSP F7 and HILAT. These observations indicate that for both northward and southward IMF, the traditional “cusp particle” signature is coincident with the region 1 Birkeland current system and maps to low altitude along field lines that thread the dayside boundary layer. The traditional “cusp” Birkeland current system flows along field lines that lie poleward of the region of cusp particles and the region 1 current system. These field lines thread the plasma mantle. Thus, we suggest that the traditional “cusp” current system might be appropriately renamed the “mantle” Birkeland current system.