Tracing of high‐latitude magnetic field lines by solar particles

Abstract

Recent measurements of solar particles in the energy interval between hundreds of keV and a few MeV have shown that a direct connection exists between a portion of the high‐latitude geomagnetic field and the interplanetary magnetic field. The access window for 300‐keV solar protons that reach the center of the polar cap may be as near as 150 R E in the downstream magnetotail. Solar protons that precipitate into the atmosphere at latitudes near the geomagnetic cutoff enter through the flanks of the magnetosphere and the nearby neutral sheet, possibly within 30 R E of the earth. Comparison of the patterns of auroral particle precipitation with the zones of access of energetic solar electrons and protons indicates that a substantial fraction of the aurora originates on field lines connected to the interplanetary field.