Energetic proton and electron dispersion signatures in the nightside magnetosheath supporting their leakage out of the magnetopause

Energetic proton and electron dispersion structures are detected at both th e dawn and dusk nightside magnetosheath near the equatorial plane using the Geotail Energetic Particles and Ion Composition instrument data. A common feature of all the exhibited examples is that the vector magnetic field pro gressively scans from northward to southward through all the latitude angle s while remaining almost within a plane intersecting the nightside magnetop ause. For such geometries, at the duskside magnetosheath, peaks in the ener getic electron flux precede those in the proton, whereas the opposite occur s at the dawnside magnetosheath. The peak fluxes of energetic protons (elec trons) are measured at the duskside (dawnside) magnetosheath whenever the v ector magnetic field points toward the central dusk (dawn) low-latitude bou ndary layer (LLBL) region of the magnetosphere. Therefore we infer that the energetic electron (proton) source is essentially spatially limited to the central dawn (dusk) LLBL. We interpret the observed dispersion structures as spatial phenomena: Energetic electrons (protons) leak out from the equat orial dawn (dusk) LLBL and then are channeled along the draped magnetic fie ld lines over the magnetopause toward spacecraft on the duskside (dawnside) . The energetic electrons (protons) are detected in the duskside (dawnside) magnetosheath for a larger range of magnetic field latitude angles. In con clusion, the leakage of energetic particles through the magnetopause seems to be a process of great importance, in parallel with the merging one.