Abstract
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 mapping method. To
demonstrate the capabilities of our technique we show and interpret
images of the first few milliseconds of two intra-cloud 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 (more than ten) 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.