The Initial Stage of Cloud Lightning Imaged in High‐Resolution.

With LOFAR we have been able to image the development of lightning flashes with meter‐scale accuracy and unprecedented detail. We discuss the primary steps behind our most recent lightning imaging method. To demonstrate the capabilities of our technique we show and interpret images of the first few milliseconds of two intracloud flashes. In all our flashes, the negative leaders propagate in the charge layer below the main negative charge. Among several interesting features we show that in about 2 ms after initiation the primary initial leader triggers the formation of a multitude (>10) negative leaders in a rather confined area of the atmosphere. From these only one or two continue to propagate after about 30 ms to extend over kilometers horizontally while another may propagate back to the initiation point. We also show that normal negative leaders can transition into an initial leader like state, potentially in the presence of strong electric fields. In addition, we show some initial breakdown pulses that occurred during the primary initial leader, and even during two "secondary" initial leaders that developed out of stepped leaders. Key Points: Our new LOFAR imaging procedure can locate over 200 sources per millisecond of flash with meter‐scale accuracyThe primary initial leader breaks up into many (>10) negative leaders of which only one or two continue after 30 msSome negative leaders propagate from the positive charge layer back to get close to the initiation point [ABSTRACT FROM AUTHOR]