Alkali emissions

Article By:

Swider, William, Jr. Space Physics Division, Air Force Geophysics Laboratory, Hanscom Air Force Base, Bedford, Massachusetts.

Last reviewed:October 2019

DOI:https://doi.org/10.1036/1097-8542.022800

Light emissions in the upper atmosphere from elemental lithium, potassium, and especially sodium. These alkali metals are present in the upper atmosphere at altitudes from about 50 to 62 mi (80 to 100 km) and are very efficient in resonant scattering of sunlight. The vertical column contents (number of atoms per square meter) of the alkali atoms are easily deduced from their respective emission intensities. First detected with ground-based spectrographs, the emissions were observed mainly at twilight since they tend to be overwhelmed by intense scattered sunlight present in the daytime. A chemiluminescent process gives rise to nightglow emissions at the same wavelengths. The development of lidars (laser radars) that are tuned to the resonance lines have enabled accurate resolution of the concentrations of these elements versus altitude for any time of the day. See also: Aeronomy; Chemiluminescence

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