Studying the relationship between substorm-onset related Pi1Bs and IPDP-type EMIC waves

The relationship between Pi1B and IPDP-type EMIC waves was first discussed in 1971 by R. R. Heacock, who found that Pi1B and IPDPs occur near-simultaneously in ground observations, though they are spatially separated; IPDPs appear at lower geomagnetic latitudes (60-65 degrees) than PiBs, which are more prominent at ~70 degrees. It is well understood that Pi1B waves are correlated with substorm onset, but it is often overlooked that IPDP-type EMIC waves can be as well; they are thought to be associated with increased fluxes of 40-60 keV substorm-injected protons, which was first modeled in 1980 by F. Sorass. Others have postulated that IPDP waves are excited by protons that undergo gradient-curvature drifting and eventually interact with the cold plasmapause population, but oft-neglected is the important role that drift-shell splitting plays in the process. Our research attempts to understand the different pathways that Pi1B and IPDPs take from their shared origin in substorm onset to their distinct observations on the ground, including the effects of drift-shell splitting en route. We present two case studies showcasing data from an array of four ground-based Antarctic magnetometers that cover the evening sector, as well as in-situ magnetometer data, proton fluxes, and proton pitch angles from the Van Allen Probes. Our observations corroborate the separation in MLAT between Pi1B and IPDPs and additionally pinpoint a separation in MLT, with IPDPs occurring roughly two hours earlier than Pi1B observations. Building from our observations we model the drift-shell splitting which injected particles undergo post-onset, with the expectation that this work will provide an improved model for the process. Finally, we have begun a statistical study of substorm-related IPDP observations that encompasses a full year of data. Preliminary results covering three months of data shows that of 41 IPDP occurrences, 36 were observed in conjunction with an enhanced AE index-- a roughly 88 percent correlation.