A Physical Model of Branching in Upward Leaders
P. Lalande (Onera), V. Mazur (National Severe Storms Laboratory)
The physical processes leading to branching and physical factors affecting branching features are poorly understood. We are applying the tested physical model of axisymmetrical leader development following the streamer-leader transition to a 3-dimensional propagation of the leader with branching. The propagation of the leader is driven by the potential drop at the leader tip. The branching occurs when the drop potential at the leader tip reaches a threshold. The space charge around the leaders self regulates the total number of active branches by reducing the available potential for the propagation. The model has been applied to simulate the time evolution of an upward leader started from a tall ground structure and developing in an electric field produced by a mature thunderstorm. We are satisfied with the fact that the results of computer simulation of branching leader closely resemble branching of upward positive leaders triggered by tall structures depicted in high-speed video images.