Effects of Ion Composition on the Excitation and Propagation of N+ EMIC Waves

Abstract:

The knowledge of heavy ion composition is essential to understand their role in regulating the near-Earth dynamics. However, measuring cold plasma, due to limitations in satellite potential and contamination of relativistic particles, and separating the species of close mass due to low mass resolution, is quite challenging. The instruments on-board current space missions (like MMS and VAPs) lack the mass resolution to distinguish between the N⁺and O⁺, and often the role of N⁺in regulating the magnetospheric dynamics, is lumped together with that of O⁺ ions. The EMIC wave observations provide an excellent opportunity as a promising plasma diagnostictool for estimation of ion composition, due to the fact that EMIC waves are sensitive to heavyions and also the wave instruments are not affected by the particle data limitations. We use the observed characteristic (cutoff, crossover and ion-ion hybrid) frequencies from Van Allen probes to infer for the first time the density of N⁺ions. We note that N⁺ions is a constant companion of O⁺and N⁺/O⁺ratio can vary from 0.1 to ~1. We also show that the presence of N⁺opens up new avenue of EMIC wave excitation and propagation, and scattering of relativistic radiation belt electrons and ring current ions.