Pi2 pulsations observed from the Polar satellite outside the plasmapause

Recently, Lee and Lysak (1999) suggested that Pi2 pulsations in the inner magnetosphere originate from plasmaspheric virtual resonances (PVR). The PVR model predicts that Pi2 pulsations are not strictly localized to the plasmasphere. Until now there have been no spacecraft observations of the PVR mode outside the plasmasphere. Motivated by the theoretical work, we examine Pi2 pulsations simultaneously observed by the Polar satellite outside the plasmapause and at the low‐latitude Kakioka (L = 1.3) station. We identify 14 events to have high coherence (> 0.7) between the compressional component (bz) in space and the horizontal component (H) at Kakioka during a 2‐month period in 1997. The H‐bz cross phase is ∼180° regardless of the satellite's distance from the plasmapause. The amplitude of the Pi2 pulsations tends to decrease with the distance. On the basis of these observations, we conclude that the PVR mode is an appropriate model for our Pi2 events observed outside the plasmasphere.