The process by which a positive and a negative ion join to form a neutral molecule or other neutral particle. In the literature of atmospheric electricity this term is applied both to the simple case of capture of free electrons by positive atomic or molecular ions, and to the more complex case of neutralization of a positive small ion by a negative small ion or a similar (but much rarer) neutralization of large ions. Recombination is, in general, a process accompanied by emission of radiation. The light emitted from the channel of a lightning stroke is recombination radiation. The much less concentrated recombinations steadily occurring in all parts of the atmosphere where ions are forming and disappearing do not yield observable radiation. The intermediate case of glow discharge may be thought of as the most diffuse case of visibly detectable recombination. The rate at which electrons, small ions, and large ions recombine is a function of their respective mobilities and of their concentrations. The former dependence is expressed in terms of the recombination coefficient of the particular ion type. See also airglow, aurora.