Comparison of two schemes for the generation of ELF/VLF waves in the HF heater-modulated polar electrojet

摘要

Abstract only given as follows. Two schemes for the generation of ELF/VLF waves in the HF heater-modulated polar electrojet have been studied. Under the illumination of an amplitude-modulated HF heater wave, the electron temperature of the electrojet is modulated accordingly. This, in turn, causes the modulation of the conductivity and, thus, the current intensity of the electrojet. Emissions are then produced at the modulation frequency and its harmonics. In one scheme, the HF heater is modulated by a rectangular periodic pulse. The other is the beat-wave scheme, namely, two overlapping heater waves have a frequency difference equal to the selected modulation frequency that is essentially equivalent to a sinusoidal amplitude modulation. The nonlinear evolutions of the generated ELF/VLF waves are determined numerically. Their spectra are also evaluated. The results show that the signal quality of the second (beat-wave) scheme is better. The field intensity of the emissions at the fundamental modulation frequency is found to increase with the modulation frequency in agreement with the Tromso experiments.