Generation of metastable oxygen atom O(1D) in sprite halos -: art. no. L14105

We propose a nighttime source of metastable oxygen atoms O(D-1) in the mesosphere. Here O(D-1) 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(D-1) 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(D-1) production in sprite halos and the dependence on day and night.