just if like me i hadn't guessed what cg and ic meant and didn't want to ask
this learned group

Types of Lightning Discharges


THE MOST COMMON TYPES OF LIGHTNING
CG

Cloud-to-ground lightning is the most damaging and dangerous form of
lightning. Although not the most common type, it is the one which is best
understood. Most flashes originate near the lower-negative charge centre and
deliver negative charge to Earth. However, an appreciable minority of
flashes carry positive charge to Earth. These positive flashes often occur
during the dissipating stage of a thunderstorm's life. Positive flashes are
also more common as a percentage of total ground strikes during the winter
months.

IC

Intra-cloud lightning is the most common type of discharge. This occurs
between oppositely charged centres within the same cloud. Usually the
process takes place within the cloud and looks from the outside of the cloud
like a diffuse brightening which flickers. However, the flash may exit the
boundary of the cloud and a bright channel, similar to a cloud-to-ground
flash, can be visible for many miles.

The ratio of cloud-to-ground and intra-cloud lightning can vary
significantly from storm to storm. Storms with the greatest vertical
development may produce intra-cloud lightning almost exclusively. Some
suggest that the variations are latitude-dependent, with a greater
percentage of cloud-to-ground strikes occurring at higher latitudes. Others
suggest that cloud-top height is a more important variable than latitude.

Details of why a discharge stays within a cloud or comes to ground are not
understood. Perhaps a flash propagates toward the Earth when the electric
field gradient in the lower regions of the cloud is stronger in the downward
direction.

Depending upon cloud height above ground and changes in electric field
strength between cloud and Earth, the discharge stays within the cloud or
makes direct contact with the Earth. If the field strength is highest in the
lower regions of the cloud a downward flash may occur from cloud to Earth.

Inter-cloud lightning, as the name implies, occurs between charge centres in
two different clouds with the discharge bridging a gap of clear air between
them.

OTHER TYPES OF LIGHTNING
There are numerous names and descriptions of various types and forms of
lightning. Some identify subcategories, and others may arise from optical
illusions, appearances, or myths. Some popular terms include: ball
lightning, heat lightning, bead lightning, sheet lightning, silent
lightning, black lightning, ribbon lightning, coloured lightning, tubular
lightning, meandering lightning, cloud-to-air lightning, stratospheric
lightning, red sprites, blue jets, and elves.



DESCRIPTION OF LIGHTNING DISCHARGE PROCESSES
With the initial breakdown of the air in a region of strong electric fields,
a streamer may begin to propagate downward toward the Earth. It moves in
discrete steps of about 50 meters each and is called a stepped leader. As it
grows, it creates an ionised path depositing charge along the channel, and
as the stepped leader nears the Earth, a large potential difference is
generated between the end of the leader and the Earth. Typically, a streamer
is launched from the Earth and intercepts the descending stepped leader just
before it reaches the ground. Once a connecting path is achieved, a return
stroke flies up the already ionised path at close to the speed of light.
This return stroke releases tremendous energy, bright light and thunder.
Occasionally, where a thunderstorm grows over a tall Earth grounded object,
such as a radio antenna, an upward leader may propagate from the object
toward the cloud. This "ground-to-cloud" flash generally transfers a net
positive charge to Earth and is characterized by upward pointing branches.



The lower part of a thundercloud is usually negatively charged. The upward
area is usually positively charged. Lightning from the negatively charged
area of the cloud generally carries a negative charge to Earth and is called
a negative flash. A discharge from a positively-charged area to Earth
produces a positive flash.

The initial breakdown and propagation are similar for intra-cloud lightning,
but the discharge generally occurs between regions of opposite charge.
Without the benefit of air conducting Earth, intra-cloud lightning does not
produce a return-stroke-like feature. Rather, it is characterized by slower
propagating "recoil streamers" and "K" changes. Nevertheless, tremendous
energy, bright light, and thunder are still produced by intra-cloud
lightning.


"Graeme" wrote in message
...
Distant lightning observed from Exmouth, could be quite a long way off,
but
is getting brighter. Frequency every 30 s or so.