For negative lightning, two very distinguished current
impulses have been characterized: impulses with fast
wavefronts, representing the overwhelming majority of
CN Tower lightning (474 impulses), and impulses with
substantially slower wavefronts and larger current peaks
(30 impulses). These slow negative impulses are found to
be either occurring in single-stroke flashes or representing
first strokes in multiple-stroke flashes.
Cumulative comprehensive statistics of the current
wavefront parameters (maximum derivative, peak and
risetime to peak) were derived for all the recorded 508
current impulses. The statistics indicated that slow
negative current strokes are characterized with
substantially high current peak, very large risetime and
substantially lower rate of rise in comparison with those of