Dayside optical and magnetic correlation events

Sudden, short-lived dayside auroral activity is often observed equatorward of the quiescent auroral oval. Several cases from the 1996 South Pole and U nited States Automatic Geophysical Observatory data were examined. In all c ases the optical events were accompanied by well-correlated magnetic impuls ive events. Most optical auroral activity was primarily in 630-nm emission (soft electron precipitation presumably of plasma sheet or magnetosheath or igin). Most optical events also show the presence of much shorter lived 427 .8-nm emission (harder electron precipitation with associated electron acce leration). In almost all events the keograms showed repeated poleward propa gation, indicating that the event started at lower latitudes and propagated to higher latitudes. The optical emissions showed distinct periodicities, which usually correlated well with the magnetic signature. All the events b egan equatorward of the preexisting quiescent aurora, indicating that they initiated in the region of closed field lines. The interplanetary magnetic field B-z, component prior to the events was either small or positive in mo st cases. The majority of the observed events were consistent with being tr iggered by interplanetary B-z or solar wind pressure change. For some event s, no specific trigger was found.