Boltek Lightning/2000 - Manual (Page 239)

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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larger values and the lower negative charge becomes
sufficiently large to induce a positive charge on the
ground below the cloud. At this point –CG strokes
will start to occur. If the updraft does not increase in
strength then the storm cell will produce mainly IC
(both +IC and –IC) flashes with –CG lightning. The
ratio of these types (IC to –CG) will be somewhere
between 1 to 1 and 4 to 1. A normal ratio for –CG
and +CG would be around 10 to 1.
2. If the updraft continues to gain strength, then not
only does the IC flash rate increase, but the updraft
starts shifting the area of negative and positive
charges to a higher altitude (elevated dipole). This
has the effect of increasing the distance to the ground
and as a result the –CC lightning rate decreases. At
this point the storm cell is borderline supercell.
3. If there is sufficient vertical shear at high altitudes,
then the top of the storm cell will be offset from the
bottom, as will the updraft. This may cause an
increase in the number of +CG strokes as the
positive charge is not shielded from the ground by
the lower negative charge. The shear also prevents
any accumulation of hail/rain in the area of the top
of the updraft that falls from choking the updraft and
the storm cell. Rotation of the updraft
(mesocyclone) is also a major contributor to the
cell’s stability. This can increase the lifetime of the
cell to hours from the normal 20 to 40 minutes of a
typical thunderstorm. This is a supercell storm.
Using these, one can classify storms into several categories.
1. minimal IC lightning – this is a weak or recently
formed cell
2. minimal IC lightning and a few +CG strokes – this is
possibly a dying storm cell