Frequency‐ and Diurnal‐Dependent Controlled Injection and Propagation of Extremely Low Frequency Waves in the Ionosphere: A Simulation Study

During controlled injection of low frequency waves using heating facilities, wave dynamics at several tens of hertz are particularly complex due to large multiple ion composition gradients and proximity to local ion cyclotron frequencies in both the lower and topside ionospheres. Frequency and diurnal‐dependent generation and propagation of shear Alfvén (SA) and fast magnetosonic (MS) waves (10–50 Hz) via an ionospheric current drive mechanism are investigated based on electromagnetic (EM) field spatial distributions and latitude–frequency spectra of wave amplitudes, Poynting vectors, and EM component ratios at selected altitudes obtained from time‐domain grid‐based simulations. We find that lower frequencies and nighttime conditions are more favorable for the generation of SA waves, with a critical frequency above which the generated SA wave energy becomes negligible compared with MS wave (∼30 Hz for nighttime and ∼15 Hz for daytime). The SA wave frequency range reaching the lower boundary of the ionosphere is limited by polarization changes near the crossover frequency, mode coupling facilitated by complex Hall conductivity and strong damping of left‐handedly polarized modes. We also find that MS waves at higher frequencies reflect at higher altitudes in the topside ionosphere, and the latitudinal asymmetry between poleward and equatorward MS wave propagation is more pronounced under daytime conditions. MS waves entering the atmosphere excite a transverse electric mode localized and dominant near the source latitude and a dominant transverse magnetic mode away from the source. Daytime ground wave intensities are generally weaker than nighttime, and this diurnal difference increases with frequency.