AMPTE CCE observations of Pi 2 pulsations in the inner magnetosphere

Magnetic field data acquired with the AMPTE Charge Composition Explorer satellite in the inner magnetosphere (L = 2–5) often show Pi 2 pulsations whose waveforms match Pi 2 pulsations simultaneously observed on the ground at Kakioka (L = 1.2). From a study of 25 such events, we find that the magnetic pulsations in the equatorial magnetosphere are dominated by poloidal‐mode oscillations. The relative phase between the compressional component at CCE and the horizontal component at Kakioka is either near zero or near 180°, with the ∼180° lag observed only when the satellite is at L > 3. This observation implies that there is a node of a radial standing wave at L > 3. We argue that the nodal structure arises from reflection of MHD fast‐mode waves at some inner boundary of the magnetosphere and discuss the relevance of the nodal structure to cavity‐mode resonances and oscillations in the inner magnetosphere forced by a source wave external to the inner magnetosphere.