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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 107, NO. A9, 1235, doi:10.1029/2001JA005081, 2002

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

Per Even Sandholt

Department of Physics, University of Oslo, Oslo, Norway


William F. Denig

Space Vehicles Directorate, Air Force Research Laboratory, Hanscom AFB, Massachusetts, USA


Charles J. Farrugia

Space Science Center, University of New Hampshire, Durham, USA


Bjørn Lybekk

Department of Physics, University of Oslo, Oslo, Norway


Espen Trondsen

Department of Physics, University of Oslo, Oslo, Norway


Abstract

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 By (−7 nT) and smaller (2 to −4 nT) Bz conditions. Ground observations of the aurora are combined with data from two overflights by the spacecraft DMSP F11 and F12 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.

Published 12 September 2002.

Index Terms: 2704 Magnetospheric Physics: Auroral phenomena (2407); 2716 Magnetospheric Physics: Energetic particles, precipitating; 2724 Magnetospheric Physics: Magnetopause, cusp, and boundary layers; 2784 Magnetospheric Physics: Solar wind/magnetosphere interactions.

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Citation: Sandholt, P. E., W. F. Denig, C. J. Farrugia, B. Lybekk, and E. Trondsen (2002), Auroral structure at the cusp equatorward boundary: Relationship with the electron edge of low-latitude boundary layer precipitation, J. Geophys. Res., 107(A9), 1235, doi:10.1029/2001JA005081.