Ion cyclotron waves in the solar wind: case and statistical studies

Abstract:

Electromagnetic waves near the proton cyclotron frequency are frequently observed in the solar wind at multiple heliocentric distances between 0.3 to 1 AU. These so-called ion cyclotron waves play important roles in transferring energies and mediating the level of temperature anisotropy of ions. For example, the waves can grow from the free energy of ion species with high temperature anisotropy, such as pickup ions, and lead to heating of the background thermal species. The wave-particle interaction in this frequency range is of high interest to solar wind turbulence studies, because the ion kinetic scale lies in the transition from the inertial range to the sub-ion dissipation range. The MMS orbits in “pristine” solar wind provide high-resolution plasma and fields measurements to advance our understanding of the wave properties and the wave-particle interactions at the ion kinetic scale. While combining the plasma and field measurements of MMS is good for case studies on the wave generation and interaction with particles, the abundant wave events detected from STEREO and PSP are suitable for statistical studies on the wave-property characteristics, such as their correlation with IMF geometries. In this paper, we perform case studies and statistical studies with these missions to advance our understanding on the role of ion cyclotron waves in the solar.