Structure of the polar electrojet antenna

Abstract

Field experiments were performed in Gakona, Alaska in August and November 2002. The ionospheric conductivity was periodically perturbed using amplitude-modulated radiation from the HAARP HF transmitter (1 MW power, 14 dB gain, 3.3-5.8 MHz carrier, 0.1-40 kHz modulation). The conductivity perturbations lead to perturbations to the natural flow of electrojet current in the lower ionosphere, resulting in ELF/VLF radiation at the modulation frequency. Measurements of the radiation, along with analytic and numerical models, suggest that a vertical loop with a scale size of 10 km is the dominant current structure excited during the experiments.