Pi2 pulsations in the inner magnetosphere simultaneously observed by the Active Magnetospheric Particle Tracer Explorers/Charge Composition Explorer and Dynamics Explorer 1 satellites

We statistically studied the spatial characteristics of Pi2 pulsations using magnetic field observations in the magnetosphere at the equatorial‐orbiting Active Magnetospheric Particle Tracer Explorers (AMPTE)/Charge Composition Explorer (CCE) and the polar‐orbiting Dynamics Explorer 1 (DE 1) satellites and on the ground at the low‐latitude station Kakioka (KAK, L = 1.23). We defined Pi2 pulsations from wavelet analysis of KAK data covering August 1984 to January 1989 and obtained 849 nightside (20:00–04:00 LT) events. For each KAK Pi2 event, we evaluated the coherence between the ground H component and the magnetospheric radial ( B ⊥R ), azimuthal ( B ⊥A ), and compressional ( B // ) components at the frequency of the ground Pi2. High‐coherence ground‐satellite Pi2 events were found most often in B // , with many of them evident at both spacecraft when CCE was located near the equator (magnetic latitude <30°) and inside of the plasmapause estimated from an empirical formula while DE 1 was located at high latitude (>30°) and outside of the estimated plasmapause. In these simultaneous CCE and DE 1 events, the B // amplitude was larger at CCE; in addition, the H‐B // cross phase was ∼0° at CCE but was ∼180° at DE 1. We show detailed analysis of one such event as well as two other events that occurred when CCE was outside of the estimated plasmapause and exhibited different coherence and cross‐phase properties at this spacecraft. Overall, the two‐satellite observations provide additional evidence of plasmaspheric virtual resonance, which was previously suggested from studies using single satellites.