ELF Waves Generated by Modulated HF Heating of the Auroral Electrojet and Observed at a Ground Distance of Approximately 4400 km

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 approximately 4-32 W. The HF-ELF conversion efficiency at HAARP is thus estimated to be approximately 0.0004-0.0032 for the 2125 Hz wave generated using sinusoidal amplitude modulation.