Inward Propagation of Flow-Generated Pi2 Waves From the Plasma Sheet to the Inner Magnetosphere

To understand the inward propagation of the Pi2 waves generated by bursty bulk flows (BBFs) from the plasma sheet to the inner magnetosphere, we statistically investigate 137 midnight conjunction events with one satellite of the Time History of Events and Macroscale Interactions during Substorms (THEMIS) in the plasma sheet and one satellite of Geostationary Operational Environmental Satellite (GOES) in the inner magnetosphere. All events have Pi2 wave enhancements associated with BBFs at THEMIS. In response, larger Pi2 wave enhancements at GOES are correlated with larger dipolarization associated with each BBF at THEMIS but not with stronger waves and flows at THEMIS. The larger wave enhancements at GOES occur preferentially under stronger solar wind driving. We discuss an explanation considering that BBFs are an earthward moving plasma sheet bubble having relatively lower flux tube entropy compared to that of the background plasma and that Pi2 waves are generated by the slowing down of the bubble. The stronger dipolarization of BBFs suggests a bubble of smaller entropy, while the stronger solar wind driving leads to higher background entropy in the inner magnetosphere, both favorable for a bubble to penetrate deeper, and thus, Pi2 waves generated by the bubble are more likely to propagate to the GOES location with less damping to result in larger wave enhancements. In addition, our analyses using empirical density and magnetic field models suggest that the strong Pi2 wave enhancements at GOES are less likely to be a cavity resonance driven inside the plasmasphere.