NORTHWARD INTERPLANETARY MAGNETIC-FIELD CUSP AURORA AND HIGH-LATITUDEMAGNETOPAUSE RECONNECTION

We present observations of two types of auroral forms located at diffe rent latitudes in the cusp region. Type 1 (south) auroras are located at similar to 71 degrees 75 degrees MLAT and occur during intervals of southward directed interplanetary magnetic field (IMF). Higher-latitu de (77 degrees - 78 degrees) type 2 (north) auroras are associated wit h northward IMF (B-z > 0). Intervals are studied which are characteriz ed by transitions from one auroral form to the other in response to IM F switches from north (clock angle < 50 degrees) to south (clock angle > 90 degrees) and vice versa. These observations are found to be cons istent with the interpretation that type south auroras are a signature of low-latitude magnetopause reconnection and that the type north aur oras are associated with high-latitude reconnection, tailward of the c usp. The latter is supported by satellite (DMSP F11) observations of p article precipitation and ionospheric convection. The simultaneous exi stence of type north and type south auroras is observed during interme diate IMF states (clock angle similar to 60 degrees). Observations of type north auroras may be used to study the relationship between the I MF B-x component and high-latitude reconnection. We find that type nor th auroras occur in the northern hemisphere for both B-x polarities. E nhanced emission intensity of the auroral green line seems to be a fea ture occurring predominantly during negative B-x conditions. The enhan ced green line intensity is considered to be an indication of low-alti tude particle acceleration in regions of strong field-aligned current intensities. Such particle accelerations (green line emission) may occ ur predominantly in regions of upward directed IMF B-y-related current s in association with the type north cusp aurora.