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.