Resonant Wave Excitations of Suprathermal Populations in the Solar Wind and Terrestrial Magnetosphere

Abstract

It is believed that the suprathermal populations of electrons and protons in the solar wind and terrestrial magnetosphere (with energies exceeding those of the bulk population up to several keV) can offer key answers to many major problems, such as the origin of energetic solar particles from interplanetary shocks, particle acceleration by the energy dissipation of the small-scale wave fluctuations, but also a certain level of kinetic turbulence which can explain the non-equilibrium quasi-stable states of space plasmas. Due to their low density and relatively high energy, these populations are collisionless, which means that their dynamics is governed by wave-particle interactions, especially resonant Landau or cyclotron interactions. We present here a series of recent results that demonstrate that the suprathermal populations, whether in the form of a less-drifting halo or the field-aligned beams/strahls, are mainly responsible for the resonant excitation of kinetic wave instabilities. The in-situ observations confirm both the electromagnetic fluctuations triggered by temperature anisotropy and the predominantly electrostatic excitations induced for instance by electron beams.