MadSci Network: Physics |
Brad, Radio is transmitted (and received) via electromagnetic waves which travel in straight lines, and can be disturbed by outside influences (other stations, car ignition systems, etc). Another influence is the earths "Ionosphere", a region of charged particals high in the atmosphere which is affected by solar radiation. When the sun is up (say, noon), emissions (and absorption) from the Ionosphere is high, causing radio interference. In the morning or evening, it's correspondingly low. At night, for instance, the Ionosphere tends to reflect radio waves, and guide them around the surface of the earth. This is why ham radio operators can communicate with people all over the planet. This is known as "Skipping" the signal (or "The Skips", for short). Now, the reason radio interference is greater in the evening, is because at morning, the surface of the earth is cool, so the Ionosphere receives energy from only the sun. But in the evening, the earths surface is warm, which radiates infrared energy up into the ionosphere, adding to the energy it's already receiving from the sun, increasing its emissions (and absorption). Hope this helps, Keith Little