Attachment process of two negative first strokes in natural lightning imaged with a high-speed video camera at the Lightning Observatory in Gainesville (LOG), Florida. Shown in (a) is the break-through (final-jump) phase. The faintly luminous formation (FLF) is a common streamer zone with an estimated average electric field of about 0.3-0.4 MV/m. Shown in (b) is most likely an 11-m-long positive UCL with a long streamer zone. In both cases the return stroke occurred in the next frame. About one-third of 50 examined records showed FLFs as seen in (a) and (b). Adapted from a paper published in JGR by M.D. Tran and V.A. Rakov (University of Florida).
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