A comparison of Pi2 pulsations in the inner magnetosphere and magnetic pulsations at geosynchronous orbit

A mechanism proposed for Pi2 pulsations in the inner (L = 2-5) magnetosphere is fast-mode waves trapped in the plasmasphere. The presence of the trapped waves can be examined using multisatellite observations in the inner and outer magnetosphere. Until now, there were few simultaneous observations of Pi2 pulsations in the different magnetospheric regions. In this study we examine two Pi2 pulsations observed in the inner magnetosphere from the Active Magnetospheric Particle Tracer Explorers/Charge Composition Explorer (AMPTE/CCE) and compare them to magnetic variations observed from the geostationary GOES 5 and 6 satellites. The first and second Pi2s were observed when CCE was located at L ∼ 3.9 and 5.0, respectively, and in the premidnight sector (∼2000-2100 magnetic local time). During both events, CCE observed strongly compressional oscillations. At geosynchronous orbit, pulsations were excited simultaneously at the onset times of the compressional oscillations at CCE. However, the transverse (b_y) component dominated, and its period differed from those of the compressional oscillations at CCE. This suggests that the oscillations at CCE and at geosynchronous orbit are excited by a common broadband source but that their generation mechanisms may be different (i.e., a trapped fast mode for the compressional oscillations at CCE and a field line resonance for the transverse oscillations at geosynchronous orbit).