ELF waves generated by modulated HF heating of the auroral electrojet and observed at a ground distance of ∼4400 km

[1] We present calibrated measurements of ELF waves generated by modulated HF heating of the auroral electrojet by the High frequency Active Auroral Research Program ( HAARP) HF transmitter in Gakona, Alaska, and detected after propagating more than 4400 km in the Earth-ionosphere waveguide to Midway Atoll. The magnitude of the 2125 Hz wave received at Midway Atoll is consistent with the radiation from a horizontal dipole located at the altitude of the maximum Hall conductivity variation (created by modulated HF heating) and radiating similar to 4-32 W. The HF-ELF conversion efficiency at HAARP is thus estimated to be similar to 0.0004-0.0032% for the 2125 Hz wave generated using sinusoidal amplitude modulation.