Ion production in the D-region

Ionization processes for the D region are reviewed. Levels of ionization range from the fairly steady rates produced through galactic cosmic rays to the large rates generated during solar flares and associated geomagnetic storms. The normal quiescent daytime D region is ionized by solar UV radiation available because of certain windows and solar X-rays, although this latter source is generally weak. Cosmic rays are important roughly below 65 km. At night, stellar X-ray sources may be important along with precipitating electrons at high latitudes from the magnetosphere. Solar flares can result in ionization rates due to X-rays, electrons or nuclei which are greatly enhanced over quiet conditions. Typical ionization production rates from these various sources are illustrated.