The High-frequency Active Auroral Research Program (HAARP) located in Gakona, Alaska, is centered around the Ionospheric Research Instrument (IRI), a high-power, high-frequency phased array radio transmitter with 180 antennas used to temporarily excite a portion of the ionosphere. Studies of these disturbances can provide insights into natural ionospheric processes and solar-terrestrial interactions​1​. The IRI operates on frequencies from 2.7 to 10 MHz and can transmit in continuous or pulsed waves, the latter being used as a radar system to measure the decay of ionospheric modifications​1​.

The HAARP facility also includes a fluxgate magnetometer, a digisonde for ionospheric profiling, and an induction magnetometer to measure geomagnetic fields​1​. It was constructed in three phases, with the final phase completed in 2007, allowing the array to theoretically reach a maximum effective radiated power (ERP) of 5.1 gigawatts​1​. Located north of Gakona, near Wrangell-Saint Elias National Park, HAARP was built on the site of a former over-the-horizon radar installation​1​.