Abstract
We report on ultra-slowly propagating discharge events with speeds in
the range 1-13 km/s, much lower than any known lightning process. The
propagation speeds of these discharges are orders of magnitude slower
than leader or streamer speeds, but faster than the ion drift speed. For
one particular event, a lightning leader forms about 40 ms later within
50 m of the discharge, likely within the same high field region. A
second slow event forms 9 ms prior to the initiation, and leads into the
negative leader. Most slow events appear to not be directly involved
with lightning initiation. This suggests that the classic streamer
cascade model of initiation is not always a definitive process. In this
work we describe these discharge events displaying unique behavior,
their relation to common lightning discharges, and their implications
for lightning initiation.