Direct Measurements of Cold Plasmaspheric Ions to Investigate Impacts on Dusk-side EMIC Waves

Abstract:

Studies on electromagnetic ion cyclotron (EMIC) waves have shown higher wave power emissions at normalized wave frequencies below the local He⁺ cyclotron frequency along Earth's dusk-side magnetosphere whereas lower wave power emissions above the local He⁺ cyclotron frequency are more often seen along the dawn-side. These broad-scale differences in wave characteristics are qualitatively understood as being a result of plasma properties differing between the magnetospheric locations. Various satellite missions have suggested increased plasma density consistent with cold plasmaspheric plasma presence along Earth's dusk-side magnetosphere as well as the moderately anisotropic hot protons that provide the free energy for wave growth as factors contributing to dusk-side EMIC wave properties. But not as many missions have been capable of directly measuring the plasma properties and wave emissions when cold, dense plasmaspheric ions are also measurable. We will discuss observations made by the NASA Magnetospheric Multiscale mission satellites when bulk plasma flows (convection or ULF waves) accelerated cold plasmaspheric ions sufficiently above the spacecraft potential energy so that cold H⁺, He⁺ and O⁺ were directly measured at the same time as dusk-side EMIC wave emissions were observed. We will demonstrate application of the complex cold and hot plasma composition data to linear wave modeling to show whether the direct plasma measurements were consistent with local wave generation and how cold plasmaspheric ions impact the wave properties. Tests of similar intervals throughout Earth's magnetosphere could be applied alongside single or multi-satellite wave analysis methods to identify a non-local wave source region or even imply non-linear wave phenomena.