Dynamics of ion energy-dispersed structures near the plasma sheet outer boundary

An analysis of energy-dispersed structures of protons and populations of electrons has been made using the Interball-2 satellite data for the apogee parts of 1579 (September 13, 1997) and 1276 (July 2, 1997) orbits. At each orbit, the satellite crossed the auroral zone twice at altitudes of 13500–19000 km moving first poleward (the first crossing) and then equatorward (the second crossing). A transformation of the types of energy-dispersed structures near the outer boundary of the auroral zone was observed at the first and second crossings: VDIS into TDIS (orbit 1579) and TDIS into VDIS (orbit 1276). The VDIS represent solitary structures of 0.3–10 keV consisting of several small-scale structures 2–5 min long, while the TDIS are repeating injections of 1–14 keV 1–3 min long with the repetition period of 2–4 min. It is shown that the VDIS-to-TDIS and TDIS-to-VDIS transformations are distinctly related to the phase of a substorm. The VDIS were observed under magnetically quiet conditions before a substorm or at the recovery phase of a substorm, while TDIS were observed during the main phase of a substorm.