Auroral structure at the cusp equatorward boundary: Relationship with the electron edge of low-latitude boundary layer precipitation

We document the correspondence between different categories of auroral forms/ activities and particle precipitation/plasma convection regimes in the 1100-1300 MLT/ 70°-77° MLAT sector during strongly negative interplanetary magnetic field B y (-7 nT) and smaller (2 to -4 nT) B z conditions. Ground observations of the aurora are combined with data from two overflights by the spacecraft DMSP F 11 and F 12 on 8 January 1999. We describe the dynamics of the aurorae in the midday sector corresponding to the particle precipitation regimes which in the literature are designated (1) the dayside extension of the central plasma sheet, (2) void, (3) the electron edge, (4) the low-latitude boundary layer (LLBL), and (5) the plasma mantle. The aurorae observed in the corresponding latitude regimes are the following: (1) the pulsating, diffuse, green line-dominated plasma sheet aurora (type 3), (2) a ∼100 km wide latitudinal gap in auroral emission, (3) and (4) the type 1 cusp aurora characterized by recurrent (T = 2-3 min) equatorward boundary intensifications (EBIs), and (5) poleward moving auroral forms. Special focus is placed on (1) the association between EBIs and the electron edge/ion cutoff observed at the equatorward boundary of the LLBL precipitation and (2) the gap in the auroral emission profile located on its equatorward side. The latter corresponds to the observed strongly depleted field-aligned electron fluxes (void), which in our view is due to the loss of plasma sheet particles along newly opened field lines. Thus, in this case study we document the auroral fine structure corresponding to the open LLBL, with its electron edge, as well as the signature of the escape of magnetospheric electrons along the adjacent field lines on its equatorward/inward side.