OBSERVATION OF A CORRESPONDENCE BETWEEN POLEWARD MOVING AURORAL FORMSAND STEPPED CUSP ION PRECIPITATION

In a case study, we document for the first time a one-to-one associati on between three amoral forms which are separated in latitude and movi ng poleward and three intervals of almost constant, but different, low -energy cutoffs in the ion precipitation in the cusp region (''stepped cusp'') precipitation. The pound observations are from Ny Alesund at 75 degrees magnetic latitude (MLAT), and the precipitation pattern is observed by the DMSP F13 satellite as it crosses the noon meridian int o the morning sector. The energy cutoffs increase with decreasing lati tude. The auroral forms brighten up at different times but at practica lly the same MLAT (similar to 73 degrees) and start fading 5 min later at similar to 76 degrees MLAT. Interplanetary conditions, monitored b y WIND, show a stable, slow, and cold solar wind with an interplanetar y magnetic field which points south and west (B-y > 0). Staircase ion precipitation signatures such as observed in this example have been su ccessfully interpreted in terms of a sequence of reconnection bursts a t the low-latitude, dayside magnetopause. The time-history of the auro ral activity observed from the ground confirms this interpretation. We exclude the possibility that the auroral forms are triggered by chang es in the interplanetary medium because the latter is very steady. In particular, the (low) dynamic pressure varies little about a mean valu e of 1.6 nPa.