Analysis of information sources in references of the Wikipedia article "High-frequency Active Auroral Research Program" in English language version.
Using the 3.6-megawatt high-frequency (HF) HAARP transmitter, the plasma clouds, or balls of plasma, are being studied for use as artificial mirrors at altitudes 50 kilometers below the natural ionosphere and are to be used for reflection of HF radar and communications signals. Past attempts to produce electron density enhancements have yielded densities of 4×10⁵ electrons per cubic centimeter (cm3) using HF radio transmissions near the second, third, and fourth harmonics of the electron cyclotron frequency. This frequency near 1.44 MHz is the rate that electrons gyrate around the Earth's magnetic field. The NRL group succeeded in producing artificial plasma clouds with densities exceeding 9×10⁵ electrons cm3 using HAARP transmission at the sixth harmonic of the electron cyclotron frequency.
{{cite web}}: CS1 maint: numeric names: authors list (link)Using the 3.6-megawatt high-frequency (HF) HAARP transmitter, the plasma clouds, or balls of plasma, are being studied for use as artificial mirrors at altitudes 50 kilometers below the natural ionosphere and are to be used for reflection of HF radar and communications signals. Past attempts to produce electron density enhancements have yielded densities of 4×10⁵ electrons per cubic centimeter (cm3) using HF radio transmissions near the second, third, and fourth harmonics of the electron cyclotron frequency. This frequency near 1.44 MHz is the rate that electrons gyrate around the Earth's magnetic field. The NRL group succeeded in producing artificial plasma clouds with densities exceeding 9×10⁵ electrons cm3 using HAARP transmission at the sixth harmonic of the electron cyclotron frequency.