What caused the formation of the sea city?

Mirage phenomenon is due to the change of refractive index of air with the change of upper and lower temperature.

Mirage phenomenon is simply that people often see the nearby oasis in the desert, but in fact the oasis is still far away, which is only caused by the distant oasis refracting into people's eyes through the air in the desert. Haicheng phenomenon is the illusion that people see the city by the sea. This city is not an illusion, but a distant city refracted into the eyes of people by the sea through the air.

Further explanation of mirage: under the irradiation of sunlight, if the air is just air, the temperature should be similar. But because the specific heat of sand is relatively small (sand is relatively hot), the air temperature near sand is relatively hot. Imagine that the temperature of air decreases from one layer to another, and the closer it is to the ground, the hotter the air is. And because the hotter and thinner the air is, the smaller the refractive index will be. The difference of refractive index will cause the refraction of light in the process of air propagation. The simple diagram is as follows: (The lighter the color, the higher the air temperature, assuming that the uneven distribution of air flow is very obvious, and the light refraction angle is exaggerated. )

Shi Hai: If the air is just the air in the sun, the temperature should be about the same. However, because the specific heat of seawater is relatively large, the air temperature near seawater is relatively cold. Imagine that the temperature of the air is increasing from layer to layer, and the air closer to the ground is colder. And because the colder the air, the greater the density and the smaller the refractive index. The difference of refractive index will cause the refraction of light in the process of air propagation.