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Low to mid frequencies, especially AM broadcasts in the mediumwave and shortwave bands (and to some extent longwave), travel most efficiently this way at night, as they act more like the Earth's natural electrical field than other higher frequencies (which act more like lightLight is electromagnetic radiation with a wavelength that is visible to the eye, or in a more general sense, any electromagnetic radiation in the range from infrared to ultraviolet. The three basic dimensions of light (and of all electromagnetic radiation), or lower ones (which act like magnetismIn physics, magnetism is a phenomenon by which materials exert an attractive or repulsive force on other materials. Some well known materials that exhibit easily detectable magnetic properties are iron, some steels, and the mineral lodestone; however, all). Because the solar windA solar wind is a stream of particles (mostly high-energy protons ~ 500 keV) which are ejected from the upper atmosphere of a star. In the solar system, the composition of this plasma is identical to the Sun's corona, 73% hydrogen and 25% helium with the "blows" the ionosphere toward the earth on the day side, and away from it on the night side, this natural radio " mirrorThis article is about the reflective surfaces. A mirror is a reflective surface that is smooth enough to be able to form an image. The best known example is the plane mirror that most people have at home. In it, a parallel beam of light changes its direct" is much higher above the surface at night – allowing skywave propagation to reflect much further.
During the daytime, mediumwave and shortwave transmissionIn communications, transmission is the act of transmitting electrical messages (and the associated phenonomena of radiant energy that pass through media). In telecommunication, the term transmission has the following meanings: 1. The dispatching, for reces travel mostly by groundwaveGroundwave is the propagation of radio waves close to the surface of the Earth. Lower frequencies, especially AM broadcasts in the mediumwave and longwave bands (and other types of radio even below that), travel most efficiently this way. This is because.