Polarization of ELF waves generated during "beat-wave" heating experiment near cutoff frequency of the Earth-ionosphere waveguide

High‐frequency heating of the ionosphere is effective for generating extremely low frequencies (ELF, 3–3000 Hz) through modulation of the auroral electrojet current. While the amplitudes of the resulting ELF waves depend on the auroral electrojet current strength, the polarization of their horizontal magnetic field remains relatively stable. In this work, we determined that at the distance of several wavelengths from an ionospheric ELF source created by two HF heating waves separated by an ELF frequency, polarization parameters are influenced by the Earth‐ionosphere waveguide. Previous experiments in the vicinity of the ionospheric ELF source have determined that the right‐hand polarization of the magnetic field measured at the ground typically prevails, whereas in this paper we demonstrate that at the distance of 660 km to the east of the European Incoherent Scatter, a circular left‐hand polarization dominates. We interpret this effect as a result of “trapping” of the left‐hand mode between the upper and lower boundaries of the Earth‐ionosphere waveguide, while the right‐hand or whistler mode leaks into the ionosphere. Key PointsELF waves generated by “beat‐wave” HF heating registered at 660 kmLeft‐handed mode is trapped in Earth‐ionosphere waveguide