Mirage: The Atmospheric Illusion

4. The Role of Atmospheric Conditions in Mirage Formation

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Mostly incorporating temperature gradients and air density fluctuations, the development of mirues is closely related to particular atmospheric circumstances. Not only does knowledge of these disorders help to understand mirages, but it also helps one to forecast their possible occurrence. The ideal setting for these optical illusions to show is produced by the interaction of temperature, air pressure, and humidity. Among the most important elements influencing mirage development is temperature inversion. Under normal circumstances, air temperature falls as one climbs height. A temperature inversion, then, can arise in some circumstances when a layer of warm air sits atop a layer of cooler air. < Superior mirages—where items seem to be hovering above their true position—have their main origin in this inversion. Common over huge bodies of water, in polar regions, and in places with notable temperature swings between day and night are temperature inversions. In inferior mirages, the reverse condition is required. A temperature gradient, or fast rise in temperature close to the earth, bends light beams upward. This is the reason inferior mirages are widespread on hot, dry locations like deserts or on heated road surfaces. The ideal conditions for light to bend and produce the illusion of water or other reflecting surfaces are created by the warm air near the ground being less dens than the colder air above. Particularly in coastal regions, humidity also influences mirage creation. Complex refractive circumstances resulting from the combination of warm, dry air from land and cool, moist air from the sea can produce detailed mirages such as the Fata Morgana. The density and, hence, the refractive index of various strata of air change with their variable moisture content. Another element influencing mirage development is atmospheric pressure. Variations in pressure can influence air density, which in turn influences atmospheric light travelability. This is especially important in explaining mirages in fast changing weather or at great altitudes. The likelihood and kind of mirages seen can be much influenced by the time of day. Many mirages are more likely during sunrise or sunset when temperature gradients are most noticeable. The sun's angle also determines how light passes through the atmosphere, so impacting the appearance and strength of mirages. The proper conditions for mirages are created in great part by geographical factors. Large flat landscapes such as deserts, calm oceans, or frozen tundra offer perfect conditions for continuous formation of temperature gradients. Coastal cliffs or mountain ranges can produce localised air conditions fit for particular forms of mirage. Knowing these atmospheric factors has uses outside only mirage explanation. Knowing temperature inversions and gradients helps meteorologists forecast air quality and weather. Pilots and sailors have to know how these factors could compromise navigation and sight. In telecommunications as well, maximising signal transmission and reception depends on knowing atmospheric refraction.