Artificial auroras can be created using an array of high-frequency transmitters. Researchers have previously done this by pumping a 3.6-megawatt beam of radio waves into the ionosphere, a region of the atmosphere a few hundred kilometres above Earth's surface. The beam was powerful enough to break electrons free of their parent atoms, creating an artificial aurora similar to that of the Northern Lights.
Now Todd Pedersen of the US Air Force Research Laboratory at Hanscom Air Force Base in Massachusetts and his co-workers have used the same transmitters in Alaska to create a glowing artificial ionospheric layer that was dense enough to move down to about 150 kilometres above Earth's surface. At this altitude, the layer could potentially be useful for long-range communications or new kinds of radar.