Evidence of Sub‐MeV EMIC‐Driven Trapped Electron Flux Dropouts from GPS Observations

For many years, it was believed that resonant interactions between electromagnetic ion cyclotron (EMIC) waves and radiation belt electrons were restricted to electron energies >1-2 MeV. In recent years, however, a growing body of experimental evidence has shown that EMIC waves can cause the scattering loss of electrons down to sub-MeV energies. Using measurements of trapped electron flux from the Global Positioning System satellite constellation, we investigate the ability of EMIC waves to cause significant depletions of radiation belt electron populations between 4 <= L* <= 5. For the first time, we present statistical evidence demonstrating global decreases in sub-MeV trapped electron flux in response to EMIC wave activity. Although we find that electron losses extend down to sub-MeV energies, we also show strong statistical support for the ability of EMIC waves to preferentially cause substantial depletions of ultra-relativistic electrons in the radiation belts. Plain Language Summary Electromagnetic ion cyclotron (EMIC) waves are a type of extremely low frequency electromagnetic wave commonly found within the Earth's radiation belts. Although it has long been known that these waves are capable of driving energetic electrons out of the belts and into the Earth's atmosphere, the energy limits of this interaction are still a matter of considerable debate. In this study, we combine many years of data from electron detectors carried by multiple Global Positioning System satellites to statistically investigate the effects of EMIC waves on radiation belt electron populations. We show that these waves are capable of causing significant decreases in electron populations at energies much lower than that has previously been considered possible. This result has important ramifications not only for our models of how radiation belt electron populations change over time, but also for our understanding of how EMIC waves are linked to chemical changes in the Earth's atmosphere. Key Points Electromagnetic ion cyclotron waves can cause measurable depletion of sub-MeV trapped radiation belt electrons Primarily sub-MeV loss observations and primarily relativistic trapped-flux depletions are not in direct contradiction We present statistical evidence of ultra-relativistic trapped electron flux depletions, confirming existing published case study results