The Role of the Dynamic Plasmapause in Outer Radiation Belt Electron Flux Enhancement

The plasmasphere is a highly dynamic toroidal region of cold, dense plasma around Earth. Plasma waves exist both inside and outside this region and can contribute to the loss and acceleration of high energy outer radiation belt electrons. Early observational studies found an apparent correlation on long time scales between the observed inner edge of the outer radiation belt and the modeled innermost plasmapause location. More recent work using high-resolution Van Allen Probes data has found a more complex relationship. For this study, we determine the standoff distance of the location of maximum electron flux of the outer belt MeV electrons from the plasmapause following rapid enhancement events. We find that the location of the outer radiation belt based on maximum electron flux is consistently outside the plasmapause, with a peak radial standoff distance of Delta L similar to 1. We discuss the implications this result has for acceleration mechanisms. Plain Language Summary We present a statistical study of the location of particles, particularly electrons, in currents around the Earth whose intensity is increased, or enhanced, rapidly (within 1 day). We use over 5 years of particle intensity and plasma density data from the Van Allen Probes satellites. We find that these quick enhancement events occur when the particles are outside the edge of the plasmasphere, an ever-changing, often asymmetric donut-shaped region of plasma around the Earth. Specifically, we find that the locations of particles are correlated with the location of plasma waves outside the plasmasphere, which supports models of electron acceleration from interactions with these waves over short periods of time. Understanding these wave-particle interactions will improve our understanding of how the plasmasphere under differing conditions can either shield Earth from or worsen the impacts of geomagnetic activity and space weather.