NUMERICAL COMPARISON OF 2 SCHEMES FOR THE GENERATION OF ELF AND VLF WAVES IN THE VHF HEATER-MODULATED POLAR ELECTROJET

Generation of ELF and VLF waves in the HF heater modulated polar elect rojet is numerically studied. Illuminated by an amplitude modulated HF heater, the electron temperature of the electrojet is modulated accor dingly. This, in turn, causes the modulation of the conductivity and t hus the current of the electrojet. Emissions are then produced at the modulation frequency and its harmonics. The present work extends the p revious one on a thermal instability to its nonlinear saturation regim e. Two heater modulation schemes are considered. One modulates the hea ter by a rectangular periodic pulse. The other one uses two overlappin g heater waves (beat wave scheme) having a frequency difference equal to the desired modulation frequency. It is essentially equivalent to a sinusoidal amplitude modulation. The nonlinear evolutions of the gene rated ELF and 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 emission at the fundamental modulation frequency is found to increase with the mod ulation frequency, consistent with the Tromso observations.