Application of Local Time Dependent Ion Composition to Observations, Modeling, and Effects of Electromagnetic Ion Cyclotron Waves

Abstract:

Numerous global magnetospheric studies on electromagnetic ion cyclotron (EMIC) waves have revealed the typical wave properties observed throughout the Earth’s magnetosphere. The observed trends in the wave properties at various geocentric distances and local time sectors, although in general agreement, elude satisfactory explanation without further details on the ambient plasma properties, the low-energy (few to ~100 eV) ions in particular. Recent studies also described techniques to deduce the presence and properties of low-energy ions and the application of such a technique to THEMIS (Time History of Events and Macroscale Interactions during Substorms) data has revealed the typical low-energy ion compositional properties throughout the Earth’s magnetosphere. Motivated by the recent work on EMIC waves and low-energy ion composition, we analyze typical wave cases observed at each local time sector by the THEMIS satellites and apply the composition techniques or the statistical low-energy ion composition data to constrain the low-energy components in modeling of each wave case in the context of linear hot plasma theory. We find that the observed waves are modeled well with hot plasma theory and both are fully consistent with the composition of the ambient plasma. Our results suggest that combined ion composition and wave measurements are critical for further assessment of the effects of the waves on energetic particles. In the cases we report on here, we find the waves could resonantly interact with electrons at energies in excess of 2 MeV and therefore do not have an effect on the dominant trapped electron population.