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

Make that every 10s

"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.

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.

Thanks for a very intresting post about lighting..never new there were
so many types. still a newbie i am

regards,

clive

flybywire wrote:
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

Cloud - Air lightning (c-a) is quite common where the lightning stroke
appears to stop in mid air. Also upward lightning from the cloud top
into the strat (see below).

Sprites, blue jets and elves are not very bright and rarely seen except
by pilots, astronauts and chasers watching from a long way away in
darkness. They are believed to originate from the ionosphere and are
part of the cloud charging process. More commonly associated with +CG
lightning originating from cloud tops. Presumably also stratospheric
lightning.

Ribbon lightning is where each lightning stroke is blown away from the
next one. The same effect is caused by camera shake and can be used for
lightning research (boys - bowen camera).

Bead lightning is when the discharge channel glows at different
intensities along its length.

Black lightning is caused by video (or eyes) overexposing to black when
the electronics or retina can't cope with the intense light. There's one
piece of footage which crops up quite frequently on these severe weather
programmes showing a black lightning discharge.

Heat, sheet and silent lightning are (usually IC) lightning strokes from
a long way away.

Ball lightning is a glowing plasma ball created by the discharge and
undoubtedly exists but unfortunately this phenomenon has been taken up
by those into ufo's, pyramid power, rods, invaders from outer space and
the phases of the moon affecting weather and serious research has been
stifled as a result.

Tube lightning (fulgarites) are cause by the lightning hitting sand and
creating tubes of glass (from memory - may be incorrect?).

Coloured lightning is caused by dust and other impurities in the
atmosphere (usually) giving the lightning stroke a reddish tint.

Les

On Tue, 28 Jun 2005 13:43:00 GMT, flybywire wrote:

lightning, red sprites, blue jets, and elves.

Quite an interesting prog on five(?) "Megalighting" last week covering
sprites and jets. Trying to pin the 2nd space shuttle crash onto
lightening, officially it was wing damage from foam off the external
tank but...

This shuttle stuff formed only a small part of the programme most was
about the discovery of sprites and latterly jets. And the link beteen
sprites and positive cloud to ground lighting. Appears that a sprite
channels energy right from a vast area of the very high atmosphere to
ground in a +ve CG strike. These strikes are tremendously powerful,
much more so than "ordinary" lighting. Stroke durations measured in
100's of mS rather than around 10mS.

--
Cheers
Dave. pam is missing e-mail

I didn't see that one. Is it the one with the stratospheric bolt
allegedly hitting the shuttle and the glider getting hammered?

Ionospheric TS charging has been postulated for a long time as charge
seperation by ice crystals rubbing against each other in an updraught
isn't enough. I had a 1969 "Practical Electronics" which the author, MA
Michaelis, thoerised that the ionosphere had something to do with it, or
at least some of it. Now lost since I moved here, there was a brilliant
electrostatic field meter too if i remember correctly.

This cannot be the only mechanism that produces lightning we've all
encountered the flash - bang - gone single single cells of shallow
vertical extent that gets nowhere nere the trop!

The ionosphere sits at around +225kv positive to ground at midday local
in fair weather and is the basis for terra's electrostatic field
measurements.

This isn't enough for a direct spark to ground else we'd all be getting
fried by superbolts on a regular basis but the cloud is going to modify
the field somewhat.

Stillings had a cracking +CG photograph originating from the anvil of a
ts - and extending miles away from the cloud - on his website and the
BBC had a few up that looked suspiciously like +CG superbolts too (the
broad channel is a giveaway as is the bolt not coming out of the cloud
base).


I'll have to get that cokebottle magnetometer or field mill built.
Plenty very powerful magnets available these days (dead hard disks!) and
using a laser pointer with a mirror and a webcam could give a very
pretty picture (:


Les

Dave Liquorice wrote:
On Tue, 28 Jun 2005 13:43:00 GMT, flybywire wrote:


lightning, red sprites, blue jets, and elves.


Quite an interesting prog on five(?) "Megalighting" last week covering
sprites and jets. Trying to pin the 2nd space shuttle crash onto
lightening, officially it was wing damage from foam off the external
tank but...

This shuttle stuff formed only a small part of the programme most was
about the discovery of sprites and latterly jets. And the link beteen
sprites and positive cloud to ground lighting. Appears that a sprite
channels energy right from a vast area of the very high atmosphere to
ground in a +ve CG strike. These strikes are tremendously powerful,
much more so than "ordinary" lighting. Stroke durations measured in
100's of mS rather than around 10mS.


--
Les Crossan,
Wallsend, Tyne & Wear
54.95N 1.5W
Home of the Wallsend StormCam and the Backup USW FAQ -
www.uksevereweather.org.uk

http://www.lightningstalker.com/weat.../thequest.html
this is a +CG superbolt.

Shows a CA strike too.

Les Crossan wrote:
I didn't see that one. Is it the one with the stratospheric bolt
allegedly hitting the shuttle and the glider getting hammered?

--
Les Crossan,
Wallsend, Tyne & Wear
54.95N 1.5W
Home of the Wallsend StormCam and the Backup USW FAQ -
www.uksevereweather.org.uk

On Tue, 28 Jun 2005 17:56:56 GMT, Les Crossan wrote:

I didn't see that one. Is it the one with the stratospheric bolt
allegedly hitting the shuttle and the glider getting hammered?

Aye.

--
Cheers
Dave. pam is missing e-mail