Orientation of the HAARP ELF ionospheric dipole and the auroral electrojet

Abstract

The HF heating facility of the High Frequency Active Auroral Research Program (HAARP), located near Gakona, Alaska, generates ELF (300 Hz ‐ 3 kHz) waves via modulated HF (2.7–10 MHz) heating of the auroral electrojet. Using two ELF/VLF receivers at ∼700 km from HAARP, the orientation of the equivalent ELF radiating ionospheric dipole is inferred from the relative strength and Earth‐ionosphere waveguide modal content of signals received. In several cases analyzed the effective HAARP electric dipole orientation is generally along magnetic east‐west direction. A new metric is introduced to evaluate the validity of the determination of source characteristics with medium and long‐range ELF/VLF measurements. Results are put into context of the auroral electrojet, indicating the possibility of studying small‐scale electrojet structure not observable with magnetometers.