Cold ion dynamics and interaction with EMIC waves near the Earth's magnetopause

The Earth’s magnetosphere is constantly supplied by plasma coming from the solar wind and from the ionosphere. The ionospheric supply is typically cold and contains heavy ions, which can be often found in most parts of the magnetosphere.

Electromagnetic Ion Cyclotron (EMIC) waves occur in the outer magnetosphere, often in association with ionospheric ions, and serve as a coupling mechanism to the ionosphere and inner magnetosphere. Using the MMS spacecraft, we investigate the dynamics of these waves when ionospheric ions are present, and resolve their motion and energy exchange with the electromagnetic fields below the ion scale. We find that ring current ions and ionospheric ions have different dynamics inside an EMIC wave packet near the magnetopause, affecting the dispersion relation of the wave. We compare the observations to linear dispersion theory, and find excellent agreement between both. Cold ions are accelerated and drain energy from the wave packet, and modify the intrinsic properties such as the wave normal angle and the polarization of the wave.