"Thunder is good,
thunder is impressive; but it is lightning that does the work"
Mark Twain
[Image: Rough schematic of
lightning types] There are several types of
lightning that can occur within and around a thunderstorm and each
has their own characteristics. The above schematic demonstrates the seven
most common species of lightning typically seen during thunderstorms, and
are explained in the subtopics below.
These different species of lightning can often occur at the same time, for
example C-Cs have a tendency to occur with an I-C, and P-Fs often occur with
C-As.
Cloud-Ground (C-G) Lightning aka: Forked Lightning
(name from: resembling a fork in the ground)
These well-known “Forked Lightning” strikes are the most dangerous of
lightning types, mainly to objects at surface level and aircraft flying at
low levels. A
C-G is a lightning channel originating from the (traditionally) negative cloud-base
and extending to the positively charged ground. These can
vary in amplitude and have the potential to cause physical and fire damage. They are a typical
for causing forest fires, blowing roof tiles apart, and of course severe
injury to humans or animals that are unfortunate enough to be caught out.
Likely environment:
cloud-base, usually between defined updraught and downdraught boundaries.
Cloud-Cloud (C-C) and Intra-Cloud (I-C) Lightning C-C aka: Spider Lightning / Streaked Lightning (name from: resembling spiders legs / lightning channels streaking across the sky)
I-C aka: Sheet Lightning
(name from: resembling a sheet of light in the sky).
Lightning also occurs within the cloud mass itself, between convergent cells
or between different cells of the storm. These lightning streaks may be
visible to the observer, or hidden from view depending on where you are
positioned around the storm cell. So Cloud-Cloud and Intra-Cloud lightning
come hand in hand and seem to be the most common type of lightning. The
difference is subtle, but C-Cs are often referred to as the streaks you see,
and I-Cs are often the ones you don't and light the cloud up in a sheet of
light. C-Cs
and I-Cs can vary greatly in magnitude depending on the
nature of the environment and cloud structure. Some will spark in
isolated regions of precipitation curtains and cloud bases with low luminosity and
producing a weak crackly thunder (Thunder
Example from T0019 mp3) indicating low-amp nature.
On the other hand some may be interconnected with various other types
throughout the storm cloud and
can sometimes be of high-amp nature with a large current with high luminance
coupled with a well-defined thunder (Thunder
Example from T0011 mp3).Likely environment: widespread, usually between the updraught and downdraught
regions, between top and bottom of a cumulonimbus tower, or between two
opposing cells.
Anvil-Crawler (A-C) Lightning
(name from: the physical appearance of lightning crawling)
This is a form of I-C/C-C of hypnotic
beauty and an eerie silence, usually seen in large thunderstorms with
massive upper-level anvil shear/spread. Occurring along the underside of
these large anvil clouds some 7000-30,000ft above the surface, the thunder from these super-massive
discharges is often unheard or very quiet depending on height. The lightning channel fans out for tens
of miles in a chain reaction as it progressively discharges large areas of charge
and encounters new areas along the way. The discharge is
often so progressive that the observer can witness the lightning literally crawl
across the sky, often with I-C flickering from the main cell. In some
exceptional cases, as observed in the past in night-time storms, there is an
internal I-C crawl within the anvil before the visible C-C crawl underneath.
Due to their complexity, if unseen, they may appear to the observer as an
I-C sheet with multiple seconds worth of return strokes. Likely environment:
widespread underneath dense sheared anvils.
Positive-Flash (P-F) Lightning aka: Anvil Lightning / Bolt from the Blue
(name from: lightning originating from the upper-anvil regions and possibly
reaching around the thunderstorm)
This type of lightning occurs when a C-G originates from a positive region
in cumulonimbus tower, which is usually found in the upper level parts near
the anvil formation. The
C-G then extends all the way to the ground from such heights like
20,000-35,000ft (up to 8-10
times the length of a normal C-G). These usually occur outside the
cumulonimbus tower, however some lightning channels choose to take an
internal path and can appear to the observer as high-amp C-Gs. The give-away is the duration
of the thunder. These illusive P-Fs can also travel great distances
around the storm cloud and appear to the observer on the surface to occur
from thin air. For example, one strike occurred at the Kennedy Space Centre
at Cape Canaveral during the summer months of 1997 which was thought to
originate from a thunderstorm 56 miles away.
Likely environment: out of
newly produced anvil mass, usually observed close to an updraught tower.
Ground-Cloud (G-C) Lightning aka: Up-Flash / Rocket Lightning (name from the apparent
motion of the lightning channel from ground to cloud)
Youtube Video of a G-C credited to Tom A Warner /
www.ztresearch.com These have been seen to sprout from the tops of tall buildings or transmitter towers.
They happen traditionally when a negatively charged region on the ground
connects to a large area of positive charge in the cloud above, usually
under the anvil mass ahead or around a storm cell where P-Fs and A-Cs may be
occurring. The illusive characteristic of these discharges
is that it appears as a progressive upward-moving Anvil-Crawler with reverse
upward-pointing branches, which is
where the slang names
“up-flash” or “rocket lightning” come from. The leader channel often has
long duration due to the progressive nature of the discharge with different
parts of the cloud and can sometimes develop into a classic Anvil Crawler.
Likely environment:
underneath strong positively charged regions (often the underside of a
large anvil) occurring near tall buildings or transmitter towers.
Cloud-Air (C-A) Lightning
This occurs when
lightning channels dissipate into clear air. This usually occurs in the
accompaniment of other lightning discharges such as P-Fs or C-Gs. The example image above shows
several channels of lightning coming from the top of an updraught tower at
the back of storm
PS0001. In the next video frame the left-most channel developed
into a P-F.
C-A strikes are rarely seen unless the thunderhead, especially the
developing parts of it, are clearly visible with no visibility obstructions,
or C-Gs occurring near the edge of the cloud.
Likely environment: around
upper regions of updraught towers.
Heat Lightning (H-L)
Heat lightning is the name given to distant flashes of I-C or “sheet” that
can be seen on the horizon but unheard. It gets its name from old folklore,
when during hot summer
months in temperate climates a thunderstorm is seen
on the horizon lightning up the atmosphere immediately
around it. Likely environment:
along thundery frontal systems or convergence zones lasting into the night.
Ball Lightning (B-L)
Most people have heard of the legendary myth of Ball Lightning, but no one
has ever got any valid evidence of its existence. It is thought to be a
plasma-ball phenomena occurring close to the ground during thunderstorms,
and usually in urban areas.
There are a handful of accounts of ball lightning events, but with no hard evidence or
scientific reasoning to solidify their existence. Some people have claimed to film
or photograph
orbs floating around cumulonimbus towers aloft, but were eventually
identified as aircraft avoiding the thunderstorm by flying around it. Likely environment:
urban areas close to the surface.
SELTZER'S LIGHTNING AMPLITUDE CLASSIFICATION
There is no current general classification of amplitudes
of lightning, so I have devised some simple terminology for describing the magnitude of a
specific lightning discharge:-
High Amp – High current; resulting in high luminance & loud thunder.
Mid Amp – Average current; resulting in medium luminance and substantial
thunder.
Low Amp – Low current; resulting in low luminance & soft thunder.
NB: When talking about the amplitude of a specific lightning discharge, it
is important to state the species of the lightning, as each have their
average strengths. For example, a mid-amp P-F is likely to be on par with a
high-amp C-G.
These terms are devised from making simple observations as follows.
Luminance
Often it is acceptable that the brighter a lightning discharge, the higher
the current. This is a general rule and isn’t always the case - it depends
on the environmental conditions and the size of the lightning channel. But
typically if a streak of lightning appears to be very faint, the current is
lower than average, and similarly if a streak appears to be bright the
current is usually higher than average.
Thunder Amplitude
The sound of the thunder, taking into account the distance in which the
original discharge occurred, can be a good indicator of the type of
lightning channel that has occurred and also the strength.
Excluding C-G for a moment, if the thunder sounds loud and defined with
substantial bangs and booms (like during T0049), this often means it has occurred
from a high-amp lightning channel. If the lightning channel has occurred at
some distance and its thunder still sounds loud, then again this indicates a
high-amp discharge. If the thunder is of a soft nature with soft rumbles or
snapping-crackles, in particular C-C (like during T0019}, then it is likely to have
come from a low-amp lightning channel.
C-Gs tend to have a unique thunder signature. Usually they are very defined
in high frequency bangs at close range due to their occurrence at
surface-pressure (higher air-pressure than in the cloud). Assuming there are
no dense rain curtains in between the lightning channel and the observer,
there is also minimal cloud damping underneath the cloud (see thunder
section) so the thunder can propagate evenly. Therefore C-Gs always appear
to have loud thunder even at a distance. This makes it difficult to
distinguish a high-amp C-G from a low-amp C-G at close range. From a
distance it is more distinguishable, as a high-amp C-G would give a
low-frequency “sonic-boom” thunder, and a low-amp would give a distant
rumble.
Electromagnetic Radiation (EMR) Pulses
Lightning emits a large spectrum of electromagnetic radiation {research
types}, including light and heat (infrared). Notable EM discharges are
usually associated with high-amp C-Gs, C-Cs, P-Fs and sometimes I-Cs. They
can be detected on radio, TV and video camera footage as interference such
as blips or snaps in the video/audio reception. If you are filming a
thunderstorm and hear a loud snap in the audio track at the same time as a
discharge, the discharge is likely to be of a high-amp nature.
