Long‐Lasting Ground‐Satellite High Coherence of Compressional Dayside Pc3–Pc4 Pulsations

Abstract

AbstractWe present observations of broadband (∼10–50 mHz) Pc3–Pc4 waves on 4 January 2014. The waves were detected on the dayside simultaneously in a compressional component (δBz) at the Radiation Belt Storm Probes A (RBSP‐A) in the inner magnetosphere and in the north‐south component (δH) on the ground at a low‐latitude Bohyun (BOH) station (L = 1.3) during an interval of small interplanetary magnetic field cone angle, suggesting that upstream ultralow frequency (ULF) waves were the source of the magnetospheric Pc3–Pc4 waves. We observed the ground‐satellite high coherence between RBSP‐A δBz and BOH δH for a prolonged time interval lasting 6.5 hr, which has not been reported previously, during which RBSP‐A was on the inbound and outbound legs moving from L = ∼3.3 to ∼6.3. In order to understand the spatial mode structure of the compressional waves, we examined the ground‐satellite cross phase for the high‐coherence interval and found that the waves observed in and out of the plasmasphere propagated earthward at the average fast‐mode speed of ∼700–1,000 km/s. We also observed cross‐phase values smoothly changing with the radial distance of the spacecraft across the plasmapause. This indicates that the presence of the plasmapause has little effect on our fast‐mode waves propagating into the inner magnetosphere and to the ground low‐latitude station.