The phenomenon of mirages is usually portrayed in deserts, but there is, even if it is rare, the formation of these images in cold places like Alaska.
Generally, when portrayed in movies or series, mirages happen in deserts or very hot places. In places where the temperature is very high, the phenomenon of inferior mirage occurs, in which the image of an object is formed in a position lower than the real position.
The occurrence of an inferior mirage, which happens in hot places. The closer to the ground, the higher the temperatures of the air layers and, consequently, the lower the density of the air .
The decrease in density causes a consequent decrease in the refractive index of the air, thus, the light coming from the object will undergo successive refractions, always from a higher to a lower refractive index. At a given moment, the angles of incidence of light rays between the layers of air become greater than the critical angles , which provides for total light reflection . In this way, the light rays make an upward curve, resulting in an image of the object in a position lower than the real position.
Mirages in Alaska
Superior mirages are produced in a reverse process to the occurrence of inferior mirages. In very cold places, such as Alaska, the layers of air close to the ground have lower temperatures compared to the layers of air immediately above.
In this way, light undergoes successive refractions as it moves to increasingly higher positions, where temperatures are higher, which provides a lower refractive index. The images generated by this rare phenomenon are formed above the real position of the object and, therefore, provoked many legends about possible flying ghost ships.
The position in which the Sun and other stars are seen in the sky is also not real. The light coming from these celestial bodies undergoes successive refractions as it passes from the less dense layers of atmosphere to the denser ones, close to the ground. Thus, the position of the observed star is always superior to its real position. This optical phenomenon is similar to the superior mirage that occurs in cold places and explains why, even after setting, the Sun can still be seen.