Highlights from Swedish Institute for Space Physics
Studies of Electromagnetic Radiation in Space
“Recently we have demonstrated experimentally that radio waves from modern radio stations are strong enough that the interaction in the reflecting region of the ionosphere is such that the plasma no longer can be thought of as a passive, reflecting mirror. A more accurate description of the ionospheric plasma is that it self-modifies weakly its reflecting properties more or less in synchronism with the radio waves that propagate through and reflect from it. The fact that the "mirror" so to speak takes an active part in the reflection process is due to weak, complicated, but important non-linear (non-proportional) properties which can lead to turbulence and perhaps even chaos in the plasma. We call this phenomenon ionospheric modification and its manifestation shows that the old, simplistic picture, based on linear models of the physical processes in plasma, is no longer adequate. Like all plasmas in nature, the ionosphere is a complex physical system and not just a passive mirror of radio signals. We have only just begun to understand this complexity and much more basic research is needed before we have an adequate knowledge of the true behavior of the ionosphere and other space plasma.”
“From below, the ionosphere is continually being irradiated with thousands of megawatts of radio waves generated by lightning strokes associated with the thunderstorms which occur in the Earth's lower atmosphere at a rate of about one hundred per second. It is also irradiated by the electromagnetic waves from the tens of thousands of broadcast, TV, utility and radar stations that are in use on the surface on the Earth. The radiated powers from the more powerful of these stations range from a few hundred kilowatts to a few megawatts. The handful of research radio facilities that use radio waves for studying the environment use the same type of transmitters with the same powers, but are so few that they contribute negligibly to the total man-made radiation. However, they are absolutely indispensable when it comes to monitoring the atmosphere and space surroundings of our planet, and for developing better tools for such investigations.”
“This dependence of the motion of the plasma particles on the direction of the external magnetic field causes what is called symmetry breaking. As a consequence of this, a magnetised plasma will, when being is subjected to external perturbations such as powerful radio waves, structure itself into long, "cigar shaped" structures orientated along the Earth's magnetic field from which a few percent of the plasma will be "snow-ploughed" away.”
“Our research has demonstrated that not only natural perturbations but also radio waves from modern high-power radio stations can have such a "modifying" effect.”
from 5 earth radii away and from conjugate hemispheres. The signals that bounce off the polar cusp are clearer than those that bounce of the magnetosphere.