Chapman shift
The Chapman layer is the theoretical area of the ionosphere at which the maximum ionization occurs if only the absorption of solar radiation is considered. It was named after Sydney Chapman .
Chapman first derived a distribution function for ionization in the ionosphere in 1932, assuming monochromatic ionizing radiation from the sun.
Emergence
If the solar ultraviolet and X-rays penetrate the upper earth atmosphere, the radiation is the most energetic, but only hits a few ionizable gas molecules. The denser the atmosphere, the more energy is given off to the surrounding matter and the greater the ionization there. However, two factors counteract ionization: on the one hand, the amount of energy available for deeper layers decreases due to the energy release, and on the other hand, the increase in atmospheric density reduces the mean free path of individual gas particles, which leads to stronger recombination . The equilibrium of the two opposing processes ionization and recombination determines the degree of ionization for the given place at the given time.
In this regard, two extreme states can be distinguished, each of which is characterized by a lack of ionization: "Maximum radiation energy, minimum number of particles" ( exosphere ) and "Minimum radiation energy, maximum number of particles" ( neutrosphere ). According to the description above, a theoretical zone of maximum electron density, the Chapman layer, forms between these two states.