Parametrization of the cosmic ray ion-pair production rate above 18 km

Cosmic rays are a significant source of ionization in the stratosphere and the lower mesosphere. Because the collision cross section of these energetic particles is small, the ion-pair production rate above 30 km is directly proportional to the atmospheric number density. Between 30 and 18 km increasing numbers of secondary cosmic ray particles cause a rapid increase in the ionization rate which is proportional to a simple power law in number density or pressure. The Earth's magnetic field also modulates the incident flux so that for magnetic latitudes below about 60° the ion-pair production rate is also proportional to a factor of (A+B sin⁴Λ).