Quasi-longitudinal whistler propagation in presence of finite ion response

In recent studies, quasi-longitudinal whistlers propagating along the resonance cone were identified to develop a steep density structure as a result of longitudinal resonant excitations in the upper-hybrid regime that are nonlinearly modified. The question of whether the ion response to these resonant whistlers in the lower hybrid regime, shared by them with ion excitations, leads to a stronger resonant coupling of quasi-longitudinal whistlers to electrostatic fluctuations remains unexplored and addressed by incorporating finite ion mobility (i.e., departure from mi→∞ limit) in present coherent quasi-longitudinal whistler simulations. At moderate angles, the ion response shows modification of lower hybrid ion excitations at the stage of evolution where the longitudinal electrostatic field of both modes grows comparable. The ratio of electron density fluctuation associated with whistler and plasma density fluctuation associated with ion response is, however, recovered to be small and confirmed analytically. In propagation along the resonance cone at high density, the ion fluctuations approach lower hybrid resonance without density steepening. Excited at equal wave numbers, they complement the longitudinal electrostatic field of the quasi-longitudinal whistlers. At higher densities, steep sharp electron density fluctuations are found recurrent and in equilibrium with the coherent lower-hybrid ion density structures.