HAARP is located in Gakona, Alaska. This location was chosen for a variety of reasons.
Alaska is located in the auroral zone, which makes the atmosphere above it unique.
The Earth's magnetic field lines connect to the solar wind in this region, which increases
the flow of solar wind particles into the ionosphere. These particles, which are
responsible for the aurora borealis, transfer energy to the ionosphere. Research on the ionosphere
in this zone provides understanding not only of the Earth's atmosphere, but also of the solar
wind and magnetosphere.
The other advantage to Gakona was its size and location on a major highway. Gakona is not densely populated, so there is less electrical and optical noise to interfere with HAARP's instruments (and vice versa: fewer chances of potential interference of HAARP's radio antennas with AM/FM radio stations and ham operators).
Image courtesy TravelAlaska.com