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 observe d 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 m agnetosonic waves having frequencies close to the gyrofrequency of the heated ions. Dynamical spectra recorded onboard the AUREOL 3 satellit e during the simultaneous occurrence of these waves and the generation of H+ conics have shown that, in such a case, resonant wave absorptio n at the gyrofrequency of the protons is likely to occur. These phenom ena are due to the propagation, reflection and subsequent conversion o f the magnetosonic waves throughout the inhomogeneous magnetospheric p lasma. Theory allows to determine the energy budget of the resonant ab sorption and to describe some features of the observed spectra. Follow ing similar ideas it is also possible to build up a theoretical scenar io aiming at explaining the transverse heating of O+ ions and the form ation of oxygen conics. As described in the experimental literature, t his likely occurs far above the topside ionosphere and thus at higher altitudes than covered by the AUREOL 3 spacecraft.