Boltek Lightning/2000 - Manual (Page 229)

R E A L - T I M E L I G H T N I N G D E T E C T I O N
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The most common type of lightning that most people are
familiar with is the negative cloud to ground discharge (-
CG). This type of lightning originates in the main negative
layer (in figure #1).
The lightning discharge begins with step leaders, a sequence
of discrete branched steps from below the negative charge in
the cloud to the ground, which ionizes the path. As it
approaches the ground (within 100 meters or more) an
induced positive charge in the ground creates a streamer
which bridges the gap and a return stroke moves up the path
created by the stepped leader. Figure 2 shows a typical –CG
stroke.
Both the stepped leader and the return stroke create
electromagnetic waves (a low frequency radio signal) that can
be heard on an AM radio as static. These signals and others
are picked up by the Boltek hardware and used in plotting the
location of the –CG stroke. It is the vertical section of the –
CG stroke near the ground that generates the signal that
allows the most accurate location of the stroke’s angular
position from the low frequency electromagnetic waves.
In most cases the path created by the stroke allows
subsequent strokes to discharge additional negative charge
from the cloud. Multiple strokes create the flickering ‘flash’
of lightning. The initial and subsequent –CG strokes
comprise a lightning flash.
Another type of more frequently occurring lightning is the
intracloud (IC) stroke. This type of stroke is shown in figure
3. It occurs between the main negative charge and the
overlaying positive charge. The stroke shown is a positive
intracloud stroke (+IC). In this case the main stroke channel
is shown as a vertical path.
In many cases the stroke channel has long horizontal
segments. The horizontal segments of the stroke create
distortions (phase errors) in the signals received and errors in
the location of the angular position can be as much as +/- 10