Spatial and temporal relations between Pi bursts and IPDP micropulsation events

Temporal and spatial relationships are found between impulsive Pi bursts occurring near local midnight and IPDP events occurring in the afternoon-evening side. The Pi burst occurring at the onset of a polar substorm is followed immediately by the IPDP event in the late evening sector. The IPDP is registered most clearly equatorward and westward of the center of the Pi burst event. This morphology is consistent with the IPDP’s generation by protons drifting westward from the midnight precipitation region. The IPDP’s appear most clearly at sites in the 60°–65° geomagnetic latitude range, whereas the Pi bursts are usually more prominent at 70°. Unstructured Pc 1–2 activity often precedes IPDP's and is most prominent near 70° latitude. If the midnight precipitation region spans both open and closed field lines, the westward drift of quasi-trapped protons on the innermost L shells may account for the IPDP events.