QUIET-TIME INTENSIFICATIONS ALONG THE POLEWARD AURORAL BOUNDARY NEAR MIDNIGHT

Radar and optical measurements from Sondrestrom are combined with sate llite and Goose Bay data in a study of the poleward edge of the nights ide auroral oval during a quiet period. The B-y and B-z components of the interplanetary magnetic field were close to zero, and the B-x comp onent was similar to 8 nT for more than 24 hours. On a large scale, th e convection and precipitation patterns remained almost constant durin g this period; on a small scale, however, the conditions were quite dy namic. At 10- to 20-min intervals the are that marked the poleward aur oral boundary intensified, and a new are appeared poleward of it. Abou t once per hour, stronger intensifications were observed. One such eve nt is examined in detail. The auroral arcs first appeared to dim, and then they brightened, with a factor of 10 increase in E region electro n density. At the time of the brightening a new arc formed poleward of all the arcs. The arcs then drifted southward at velocities of simila r to 270 m/s. A plasma drift disturbance, characterized by a doubling of the southward velocity and a reversal in the east-west component, p ropagated westward at 900 m/s through the fields of view of the Sondre strom and Goose Bay radars. A simultaneous satellite overpass close to the radars revealed the presence of an energetic ion event similar to the ''velocity dispersed ion structures'' observed on the Aureol sate llite and presumed to be the signature of fast ion beams within the pl asma sheet boundary layer. The stronger are intensification events obs erved by the Sondrestrom radar are associated with an increase in plas ma flow across the boundary between open and closed magnetic field lin es. We interpret this increased flow as the ionospheric signature of a brupt, localized increases in the reconnection rate in the midnight se ctor.