Study of ELF/VLF wave generation by HF heater-modulated electrojet

Summary form only given. The generation of ELF/VLF waves by the modulation of the electrojet by a powerful HF heater is of current interest. It is done by applying an amplitude modulated HF heater to modify the electron temperature of the electrojet in time. This in turn causes the modulation of the conductivity and thus, the electrojet current. Emissions are then produced at the modulation frequency and its harmonics. The present work extends the work of Kuo and Lee (1993) and Kuo (1993) of thermal instability to the nonlinear saturation regime. Two heater-modulation schemes are considered. One, corresponding to the one adopted in the Tromsq heating experiments (Stabbe et al., 1981), modulated the heater by a rectangular periodic pulse. The other one needs two overlapping heater waves (beat wave) having a frequency difference equal to sinusoidal amplitude modulation and is the approach adopted in the Arecibo heating experiments. 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 beat wave scheme is better. The field intensity of the emission at the fundamental modulation frequency is found to increase with the modulation frequency, consistent with the Tromsq results.