Ion Heating by Resonant Absorption of Electromagnetic Waves in Multi-Ionic Plasmas: A Process for the Formation of Ion Conics

Conical distribution of both light and heavy ions are commonly observed in the magnetospheric plasma at various altitudes above the auroral regions and in the cusp/cleft region. The occurrence of these “conics” is shown to be well correlated with the presence of low frequency magnetosonic waves having frequencies close to the gyrofrequency of the heated ions.Dynamical spectra recorded onboard the AUREOL 3 satellite during the simultaneous occurrence of these waves and the generation of H⁺ conics have shown that, in such a case, resonant wave absorption at the gyrofrequency of the protons is likely to occur. These phenomena are due to the propagation, reflection and subsequent conversion of the magnetosonic waves throughout the inhomogeneous magnetospheric plasma. Theory allows to determine the energy budget of the resonant absorption and to describe some features of the observed spectra.Following similar ideas it is also possible to build up a theoretical scenario aiming at explaining the transverse heating of O⁺ ions and the formation of oxygen conics. As described in the experimental literature, this likely occurs far above the topside ionosphere and thus at higher altitudes than covered by the AUREOL 3 spacecraft.