Generation of metastable oxygen atom O( 1 D) in sprite halos

We propose a nighttime source of metastable oxygen atoms O( 1 D) in the mesosphere. Here O( 1 D) atoms are generated by electron impact dissociation of O 2 molecules in sprite halo events, where electrons are accelerated in strong electric fields associated with lightning discharges. The peak production rate of O( 1 D) in a single sprite halo event is estimated to be as large as 10 4 cm −3 for a duration of 1 ms, which is comparable to, or even larger than, the steady rate by solar‐UV radiation. We also discuss the altitude dependence of O( 1 D) production in sprite halos and the dependence on day and night.