QUASI-PERIODIC POLEWARD MOTIONS OF SUN-ALIGNED AURORAL ARCS IN THE HIGH-LATITUDE MORNING SECTOR - A CASE-STUDY

This is the first payer which reports the characteristics of quasi-per iodic poleward motions of Sun-aligned auroral arcs in the high-latitud e morning sector. The moving arcs are observed from ground-based stati ons at magnetic latitudes (MLAT) of 78 degrees and 84 degrees during m agnetically quiet intervals (interplanetary magnetic field B-z similar to 0 or > 0). The arcs move poleward repeatedly with a period of seve ral minutes and a velocity of similar to 400-500 m/s and disappear at around 85 degrees MLAT. For the event observed at 78 degrees MLAT, the arcs are repeatedly detached from a stable aurora which is located at the equatorward of the arcs. The moving arcs correspond to accelerate d electrons observed by the Exos D satellite. The stable aurora corres ponds to continuous precipitation of high-energy electrons which proba bly originate from the inner part. of the plasma sheet. The ion drift data from the DMSP-F11 satellite show that the poleward moving arcs ar e located around the boundary of the large-scale sunward flowing regio n at lower latitudes and the antisunward flowing region at higher lati tudes. From these results, we conclude that the area are connected to the boundary region between the plasma sheet and the low-latitude boun dary layer in the morningside tail flank. Several mechanisms which can produce the observed motions of the arcs are discussed.