Generation of Pi2 pulsations by bursty bulk flows

Abstract

We present the first observations directly relating bursty bulk flows (BBFs) to Pi2 pulsations. At ISEE 2, a large earthward flow was observed. The Institute of Geological Sciences (IGS) magnetometer chain located at the same local time as ISEE 2 recorded Pi2 pulsations, slightly delayed relative to flow onset, consisting of a long-period (7-8 mHz) component associated with oscillations of the substorm current wedge. We demonstrate that the ionospheric current began to increase 90 s before the arrival of these Pi2 pulsations. We argue that this precursor was generated by earthward convection of plasma sheet plasma. Phase skips at midlatitudes on the nightside are associated with new flow bursts at ISEE 2. The Air Force Geophysics Laboratory (AFGL) magnetometer chain, which was located on the dusk flank, measured Pi2 pulsations that started ∼90 s after the flow bursts. We demonstrate that there is a one-to-one correlation between impulsive flow onset in the tail and Pi2 pulsations. We also show that oscillations at AFGL are directly related to temporal variations of the flow. Thus we suggest that the characteristic frequencies of low-latitude Pi2 pulsations are established by the temporal structure of processes in the near-Earth magnetotail. Copyright 1999 by the American Geophysical Union.