Observation and Modeling of Dart Leader Development in an Altitude‐Triggered Lightning Flash

The dart leader development process of an altitude‐triggered lightning flash with eight return strokes was analyzed. The analysis, based on the high‐speed camera and electric field data, revealed three different processes of dart leaders: (a) normal dart leader process; (b) dart leader process with chasing leader; and (c) dart leader process with bidirectional leader. These dart leaders are very different in terms of the average 2‐D speed and the electric field change. Moreover, in the bidirectional leader process, the 2‐D speed of the upward positive leader is greater than that of the downward negative leader. A piecewise‐speed source‐charge model was used to simulate the electric field change of the normal dart leader. The superposition of downward positive leader was used to simulate the fading and decaying process of the leader tail, which appeared in the chasing leader and bidirectional leader. The bidirectional leader model was used to simulate the bidirectional leader process, and the final simulation results are in good agreement with the measured electric field.