Kinetic Effects of Cold Plasma on Magnetospheric EMIC Waves

International audienceThe Earth's magnetosphere is populated by particles coming from the Earth's ionosphere and the solar wind. The ionospheric component is often composed by cold (below tens of eV) ions, and it has been shown that these cold ions introduce a shorter length-scale into plasma processes like magnetic reconnection, owing to their smaller gyroradius than hot magnetospheric ions. In addition, Electromagnetic Ion Cyclotron (EMIC) waves do 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 fleet, we investigate the dynamics of these waves when cold ions are present, and compare them to cases without the cold ion component. The short separation between spacecraft plus the high time resolution of MMS allows us to resolve the kinetic properties of these waves with unprecedented detail. When cold ions are present, the wave becomes kinetic to the (hot) ring current ions, whereas the cold ions remain largely magnetized. This results into cold ion trapping that produces density enhancements, which in turn may be linked to the generation of whistlers