On presentation of lightning flash in thundercloud as collective   spontaneous radiation (superradiation) pulse
  In this paper we conjecture that some specific properties of an electroactive region of thunderclouds play the major role in an initiation of a lightning flash. The electroactive region is modeled here as a quantum two-level system of oxygen molecules which are assumed to have two (ground and excited) states, where transitions from ground to excited states come as a result of micro-discharges between ice particles. In this case lightning flash corresponds to the pulse of collective spontaneous radiation caused by the deexcitations of excited oxygen molecules from metastable state into ground state. 
M.D.Scherbin