Atmospheric duct by the ionosphere. The reduced refractive index due to lower densities at the higher altitudes in the Earth's atmosphere bends the signals back toward the Earth. Signals in a higher refractive index layer, "i.e.," duct, tend to remain in that layer because of the reflection and refraction encountered at the boundary with a lower refractive index material. In some weather conditions, such as inversion layers, density changes so rapidly that waves are guided around the curvature of the earth at constant altitude. Phenomena of atmospheric optics related to atmospheric ducting include the green flash, Fata Morgana, superior mirage, mock mirage
Atmospheric model Atmospheric model An atmospheric model is a mathematical model constructed around the full set of primitive dynamical equations which govern atmospheric motions. It can supplement these equations with parameterizations for turbulent diffusion, radiation, moist processes (clouds and precipitation), heat exchange, soil, vegetation, surface water, the kinematic effects of terrain, and convection. Most atmospheric models are numerical, i.e. they discretize equations of motion. They can predict microscale phenomena such as tornadoes and boundary layer eddies, sub-microscale turbulent flow over buildings, as well as synoptic and global flows. The horizontal domain of a model is either "global", covering the entire Earth, or