Transient auroral events near midday: Relationship with solar wind/magnetosheath plasma and magnetic field conditions

Ground-based observations of auroral/geomagnetic transient events near magnetic midday and magnetosheath magnetic field and plasma observations from spacecraft IMP 8 are presented. One category of event is characterized by a sequence of discrete auroral arc fragments moving westward along the poleward boundary of the persistent cusp arc, accompanied by an isolated magnetic pulse at latitudes close to the auroral event. This phenomenon occurs mainly during intervals of southward directed magnetosheath/interplanetary magnetic field. The auroral display in the second category of event is separated in two components, possibly associated with the cusp and the cleft/low-latitude boundary layer. Intensification of the cleft aurora and magnetic perturbations over a wide latitudinal range were observed after a sharp northward magnetosheath magnetic field transition and a large variation in plasma density. It is suggested that these different events are ionospheric footprints of different time-dependent coupling processes near/in the magnetopause boundary layer. However, the specific mechanism involved (e.g., flux transfer events or pressure pulses/boundary waves) may not be uniquely inferred from these observations