The Earth is a Strong Radio Source even without Man's Tinkering
Radio telescopes, such as the mammoth 1000 ft. diameter receiver at Arecibo Observatory in Puerto Rico, have enabled scientists to detect strong radio waves emanating from such familiar bodies as Jupiter and the Sun, and more elusive distant objects such as pulsars and quasars.
It was therefore somewhat of a surprise when it was found that the earth itself radiated more radio-wavelength energy into outer space than even the mighty planet Jupiter itself. This holds especially true when it is considered that, although scientists can "see" and measure the waves from the extraterrestrial bodies from observatories on the surface of the earth, they are unable to detect the ones (except those artificially produced) that the earth itself propels into space.
We know, of course, that man-made radio and TV signals continually race outward into space, but it was not until 1974 that D.A. Gurnett of the University of Iowa reported, from satellite observations, that intense unidentified radio waves were also being emitted from the earth itself. This radiation carried the enormous power of about one billion watts--ten times that emitted from Jupiter. For comparison, the peak power emitted from the Arecibo antenna or the one at the Chatanika radar site north of Fairbanks is about three million watts, and the powerful radio station KJNP in North Pole emits only fifty thousand watts.
But why doesn't this high-powered radiowave emission disrupt communications on the ground? The simple reason is that it never reaches the ground--only the upper ionosphere. The lower ionosphere (about 100 kilometers altitude) is where most auroras occur.
It is likely that the high-speed electrons emanating from the sun that are responsible for the aurora also produce the radio signals. Fortunately, the wavelength of their vibration is so long (about 1 kilometer, or 0.6 miles) that they cannot penetrate the ionosphere. Therefore they cannot be detected at the surface and are, in effect, bounced back into space.
