MULTIPLE, DISCRETE ARCS ON SUNWARD CONVECTING FIELD LINES IN THE 14-15 MLT REGION

Ionospheric plasma flow measurements and simultaneous observations of thin (approximately 0.2-degrees invariant latitude (ILAT)), multiple, longitudinally extended auroral arcs of transient nature within 74-degrees-76-degrees ILAT and 1030-1130 UT (approximately 14-15 MLT) on January 12, 1989, are reported. The auroral structures appeared within the luminous belt of strong 630.0-nm emissions located predominantly on sunward convecting field lines equatorward of the convection reversal boundary as identified by the European Incoherent Scatter UHF radar. The events occurred during a period of several hours quasi-steady solar wind speed (approximately 700 km s-1) and a radially orientated interplanetary magnetic field (IMF) with a weak northward tilt (IMF B(Z)>0). These typical dayside auroral features are related to previous studies of auroral activity related to the upward region 1 current in the postnoon sector. The discrete auroral events presented here may result from magnetosheath plasma injections into the low-latitude boundary layer (LLBL) and an associated dynamo mechanism. An alternative explanation invokes kinetic Alfven waves, triggered either by Kelvin-Helmholtz instability at the inner (or outer) edge of the LLBL or by pressure pulse induced magnetopause surface waves.