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Creation of visible artificial optical emissions in the aurora by high-power radio waves

Abstract

Generation of artificial light in the sky by means of high-power radio waves interacting with the ionospheric plasma has been envisaged since the early days of radio exploration of the upper atmosphere, with proposed applications ranging from regional night-time street lighting to atmospheric measurements1. Weak optical emissions have been produced for decades in such ionospheric ‘heating’ experiments, where they serve as key indicators of electron acceleration, thermal heating, and other effects of incompletely understood wave–particle interactions in the plasma under conditions difficult to replicate in the laboratory2. The extremely low intensities produced previously have, however, required sensitive instrumentation for detection, preventing applications beyond scientific research. Here we report observations of radio-induced optical emissions bright enough to be seen by the naked eye, and produced not in the quiet mid-latitude ionosphere, but in the midst of a pulsating natural aurora. This may open the door to visual applications of ionospheric heating technology or provide a way to probe the dynamics of the natural aurora and magnetosphere.

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Figure 1: A pair of all-sky images taken 5 s apart showing the dynamic natural background aurora pulsating in long bands over most of the sky.
Figure 2: Images from the HAARP telescope wide field camera showing speckle-like artificial optical emissions superimposed on the background aurora only during frames when the transmitter was on.
Figure 3: Calibrated measurements from the HAARP imager showing the intensities of various auroral emissions including the oxygen green line, which was well above the threshold for detection by the naked eye during the experiment.

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Acknowledgements

HAARP is a Department of Defense programme operated jointly by the US Air Force and US Navy. We thank E. Mishin for his contributions to the experiment planning and P. Ning for operating the all-sky imager.

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Correspondence to Todd. R. Pedersen.

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Pedersen, T., Gerken, E. Creation of visible artificial optical emissions in the aurora by high-power radio waves. Nature 433, 498–500 (2005). https://doi.org/10.1038/nature03243

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