Formation of a 3-D Oscillatory Current System Associated With Global High-Correlation Pi 2 Event: A Case Study

We present a typical example of the formation of a three-dimensional (3-D) oscillatory current system associated with a global high-correlation Pi 2 event. The time variation of the field-aligned current (FAC) density in the magnetosphere is estimated using multisatellite magnetic field data in the near-Earth plasma sheet (~10 R_E, ~23 MLT). Pi 2 pulsations, which were accompanied with the development of the upward and downward FACs in the substorm current wedge, were observed at mid-latitude stations in the pre-midnight sector (20.6 and 22.6 MLT), and the periodicity of the FAC fluctuations was correlated with the estimated current-density fluctuations in the near-Earth plasma sheet. Compressional signals of the Pi 2 pulsation were observed by an equatorial ground station and a geosynchronous satellite located in the midnight sector (0.1 and 0.4 MLT). A detailed comparison of the Pi 2 waveforms, which were simultaneously observed on the ground and in the near-Earth magnetosphere, revealed high correlations between the fluctuations of the FACs and compressional pulses. These observations strongly suggest the formation of a 3-D oscillatory current system associated with the global high-correlation Pi 2 event. The sources of the oscillatory current system and compressional pulses were confirmed to be closely coupled with one another.