A new mechanism of whistler wave generation by Amplitude modulated HF waves in the polar electrojet

It is shown that a spatially distributed mode current of whistler waves, oscillating at the modulation frequency of the ground-transmitted powerful HF wave, can be induced in the E-region of the high-latitude ionosphere through the coupling between HF wave-modulated electrojet current and induced density irregularities. As shown in Kuo et. al. [1999], these density irregularities generated by the HF wave via a thermal instability vary periodically along the geomagnetic field. This current produces whistler waves directly rather than through an antenna radiation process. This mechanism generates whistler waves in the VLF range (3-30 KHz) with reduced harmonic components. The frequencies of produced whistler waves depend on the polarization, frequency, power, and modulation scheme of the HF wave. It is predicted that whistler waves at frequencies around 25 KHz can be most favorably excited, awaiting the corroboration of future ionospheric heating experiments.