The First Observation of N⁺ Electromagnetic Ion Cyclotron Waves

Observations from past space missions report on the significant abundance of N⁺, in addition to those of O⁺, outflowing from the terrestrial ionosphere and populating the near-Earth region. However, instruments on board current space missions lack the mass resolution to distinguish between the two, and often the role of N⁺ in regulating the magnetosphere dynamics, is lumped together with that of O⁺ ions. For instance, our understanding regarding the role of electromagnetic ion cyclotron (EMIC) waves in controlling the loss and acceleration of radiation belt electrons and ring current ions has been based on the contribution of He⁺ and O⁺ ions only. We report the first observations by Van Allen Probes of linearly polarized N⁺ EMIC waves, which confirm the presence of N⁺ in the terrestrial magnetosphere, and open up new avenues to particle energization, loss, and transport mechanisms, based on the altered magnetospheric plasma composition.