Fukuoka, Japan has an island like a floating sea. Do you know how a mirage is formed?

There is a low-quality mirage in Fukuoka, Japan, and Xuanjie Island is like a floating island. ?

The principle of phantom formation

Formation condition

A mirage in the desert is a refraction phenomenon when sunlight meets air with different densities. In the desert, the sand is baked by the sun during the day, and the temperature on the surface of the sand layer rises rapidly. Due to the poor heat transfer performance of air, when there is no wind, the vertical temperature difference over the desert is very significant, with high air density in the upper layer and low air density in the lower layer. When sunlight enters the low-density air layer from the high-density air layer, the speed of light changes, and after the refraction of light, the oasis in the distance appears in front of people. On the sea or river, this kind of "mirage" phenomenon happens from time to time.

A mirage is an optical illusion, a virtual image formed by the refraction of light reflected by objects on the earth through the atmosphere. Phantom is a mirage for short. According to the principle of physics, a mirage is because different air layers have different densities, and the refractive index of light in air with different densities is different. That is, because the density between the cold air on the sea surface and the warm air at high altitude is different, the light is refracted.

kind

Mirage is an abnormal refraction phenomenon, which is the result of light propagation and refraction in the atmosphere with different vertical densities. It is often divided into upward, downward and sideways mirage.

Any image or illusion that seems to reflect from the air layer in the sky is called a mirage. Mirages in the world often appear at sea and in places covered with snow and ice in the north. This is because the surface consumes heat when seawater evaporates, and the temperature of seawater rises slowly. In areas covered with snow and ice, because the snow and ice can reflect most of the sunlight and consume a lot of heat, the temperature in the lower layer becomes very low, so these places are most prone to strong inversion. If there is a strong inversion in the near-surface layer, the air density will decrease rapidly with the height, and light will spread in the air layer where the temperature increases with the height, so that the air density will decrease sharply with the height and bend downward. The light emitted by buildings on the distant horizon will enter the eyes of observers after refraction, and a mirage will appear.

Any image or illusion that looks like an object reflected from the ground is called a mirage. The next mirage will appear in the desert in hot season or in the sea area with warm ocean currents in winter. On a sunny day, it is partly cloudy and windy. When the sun shines on the dry sand, the specific heat of the sand is small and the soil temperature rises rapidly. There is almost no water evaporation here, and the heat transfer of soil molecules is extremely slow, and the heat is concentrated in the surface layer, so the air temperature near the soil layer also rises rapidly, but the upper air is still very cold. When the near-surface layer is a strong cooling layer, the temperature decreases rapidly with height, and the air density increases rapidly with height. However, when light propagates in the gas layer whose temperature decreases with height, it will bend upward. The light from the distant horizon will be refracted and directly enter the observer's eyes, and a mirage will appear.

When the atmospheric density in the horizontal direction is so different that the atmospheric refractive index in the horizontal direction is so different, a horizontal mirage may appear.

In a word, mirage is a very interesting phenomenon of refraction and reflection.