''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. The intensity of the HF signal in the ionosphere is less than 3 microwatts per cm2, tens of thousands of times less than the Sun's natural electromagnetic radiation reaching the earth and '' '''hundreds of times less than even the normal random variations in intensity of the Sun's natural ultraviolet (UV) energy which creates the ionosphere'''. ''The small effects that are produced, however, can be observed with the sensitive scientific instruments installed at the HAARP facility and these observations can provide new information about the dynamics of plasmas and new insight into the processes of solar-terrestrial interactions.'' | ''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. The intensity of the HF signal in the ionosphere is less than 3 microwatts per cm2, tens of thousands of times less than the Sun's natural electromagnetic radiation reaching the earth and '' '''hundreds of times less than even the normal random variations in intensity of the Sun's natural ultraviolet (UV) energy which creates the ionosphere'''. ''The small effects that are produced, however, can be observed with the sensitive scientific instruments installed at the HAARP facility and these observations can provide new information about the dynamics of plasmas and new insight into the processes of solar-terrestrial interactions.'' |