The HAARP Ionospheric Research facility will be a major Arctic facility for conducting upper atmospheric research. The facility will consist of two essential parts:
1) A high power transmitter, and antenna array operating in the High Frequency (HF) range, and
- A complete and extensive set of scientific instruments for observation of both the background auroral ionosphere and of the effects produced during active research using the transmitter system. Output from these instruments will be combined into an integrated data package which will be available world-wide in near real time over the internet.
During active ionospheric research, the signal generated by the transmitter system is delivered to the antenna array, transmitted in an upward direction, and is partially absorbed, at an altitude between 100 to 350 km (depending on operating frequency), in a small volume a few hundred meters thick and a few tens of kilometers in diameter over the site.
One of the research areas for HAARP will be the study of methods and techniques for the generation of extremely low frequencies (ELF) through ionospheric heating.
One of the major areas of interest in active ionospheric research is the generation of frequencies below approximately 5 kHz through interaction with the naturally occurring currents flowing at auroral latitudes.
These currents, which originate in the magnetosphere, flow near the equator side limit of the visible aurora at the altitude of the E layer (approximately 100 km)
The polar electrojet, as this phenomenon is called, carries currents that often exceed a million amperes. The current is distributed within a sheet 100 km or more wide so that the current density in any given region of the layer is low.
The latitude at which the polar electrojet is overhead is dependent on the time of day (since the current flows in a roughly circular arc centered on the magnetic pole which, in turn is offset from the geographic pole).
The equatorward extent of the polar electrojet is also a strong function of solar activity, reaching lower latitudes during active and storm level conditions and receding to the north as the geomagnetic field becomes quiet.
Depending on the time of day, the current may be flowing east-to-west or west-to-east.Active ionospheric techniques are able to temporarily affect a small portion of the layer in which the electrojet flows causing a minute change in the bulk electrical conductivity of that region.
Because electrical current tends to favor higher rather than lower conductivity media, current flowing through the affected volume will decrease slightly relative to the current flowing through surrounding unaffected regions.
When the stimulation is removed, the electrical properties in the volume under study rapidly return to ambient levels and the electrojet currents return to their natural distribution.
The rate at which the conductivity can be increased and decreased is a critical physical parameter because it determines the highest frequency at which variations can be induced onto the current flowing within the study volume.