Dayside auroral dynamics: South Pole - AMPTE/CCE observations

Coordinated observations were made between the South Pole Station 630-nm all-sky imager and the Active Magnetospheric Particle Tracer Explorer (AMPTE) CCE satellite when it was at 9 R-E apogee in the midday sector in an effort to understand the variety of dynamical changes at the magnetopause that map to the dayside aurora. On June 18, 1988, three events were observed. The first, at 1150 MLT, was a local event showing a rotation of the magnetic field and the sudden appearance of low-energy electrons indicating the satellite entering the magnetosheath or low-altitude boundary layer. This event was preceded by a type of poleward expansion of the aurora which had been previously interpreted as a possible signature/footprint of a flux transfer event (FTE), Although the magnetic field signatures at the satellite are not characteristic of an FTE, the event could be a magnetic field change produced by an FTE, which after some delay propagated to the vicinity of the satellite. The foot of the field line containing the satellite was at some distance from the south pole meridian, The second event, starting at 1610 UT (1240 MLT), was a clear case of field erosion during which the satellite entered the magnetosheath characterized by a reduction in energetic electrons, an increase in soft electrons, and a decrease in the magnetic field strength accompanied by an equatorward motion of the aurora. The third event, in the afternoon at about 1900 UT (1530 MLT), showed similar changes in the electron fluxes and similar equatorward motion of the aurora. However, this event was associated with an increase in the magnetic field at the satellite. Such a field increase could be characteristic of a pressure pulse. However, there was a corresponding equatorward motion of the aurora, which suggests that the event was also a flux erosion event in which the fringing fields of the region 1 current system, which normally cause a field depression at the subsolar region, created an increase in the field at the CCE satellite near the late afternoon side. The latitudinal (equatorward) movements of the aurora for all three events were strongly correlated with the global AE index which was dominated by stations in the dawn/dusk sectors.