Excitation of periodic magnetic field variations by radiation of amplitude-modulated high-frequency waves into the polar ionosphere

High-power HF radio waves radiated into the ionosphere strongly enhance the electron temperature. This electron heating can cause perturbations in the conductivity tensor via an enhancement of the collision frequency or the electron density depending on the modulation frequency of the HF wave. The periodically altered conductivities result in an ac current that emits electromagnetic waves. An experiment with modulation frequencies between 0.7 and 9 Hz is studied in detail and compared with numerical calculations. It is found that ellipticity and orientation of the polarization ellipse of the measured magnetic field disturbance can be ascribed to the effects of the temperature and density modulation. However, the measured amplitudes are one order of magnitude below the modeled ones, since the additionally excited induction current must be ignored in the model.