Transcript LIGHTNING

LIGHTNING
Background Information
• Lightning occurs about 2000 times at any one moment.
• Thunderstorms thrive under certain conditions. The two most basic
elements that cause a thunderstorm to develop are:
– Moisture
– Rapidly rising warm air
• A lightning flash is composed of a series of strokes with an average
of about four. The length and duration of each lightning stroke vary,
but typically average about 30 microseconds. (The average peak
power per stroke is about 1012 watts). Occurs when the air can’t
insulate the charges any longer.
• When the potential becomes great enough, electricity punches its
way through air that normal insulates, and builds a narrow bridge of
electrified gas or plasma.
• The current burrows its way in search of an oppositely charged
region where the imbalance can be relieved. When the two are
joined, current flows freely and ionizes even more air on its path,
thus creating the glowing hydra that we see as a lightning bolt.
• NCAR found that clouds become electrified only after significant
amounts of ice particles and supercooled water form at heights
above the freezing level.
• Negative cloud charge tends to develop in cells or blobs, rather than
the uniform layers previously theorized.
Lightning Bolts
•
Happens in a series of stages. First, a faint step leader emerges from the base of the
cloud, moving towards the ground in steps of 50 meters or so. Branching as it goes
down, which is why so many lightning bolts "fork".
•
As the step leader nears the ground, it attracts "streamers" of positive charge from
the ground. When it finally connects with one of these streamers, a brilliant return
stroke occurs as the charge drains out of the ionized path. The return stroke travels
upwards as the ground charge goes first. This process can be repeated up to 40
times, which is why so many seem to flicker.
Some chemistry about lightning
• When lightning occurs, sometimes you can smell it.
Intense heat & electrical current produce mini-chemical
factory where O2 and N2 are broken down into ions.
Some reform into O2 and N2 but a significant number
form Nitrous oxide compounds.
• O2 + N2
, NOx
electric current + intense heat from lightning
O 2 + N2
NO , NO2
• In the 1983 Global Troposphere Experiment, aircraft sampled the air
inside two cumulonimbus clouds and found that the levels of NO had
risen 50-fold, from 20 to 1000 parts per trillion.
• If this proves to be true
of all thunderclouds, then
lightning especially cloud-to
-cloud flashes closer to the
stratosphere could be a
significant producer of
chemicals that deplete the
Earth's protective ozone
layer.
Theories
• Scientists know that lightning occurs due to a separation of charged
particles, but the mechanism behind acquiring the charges still
remains unknown. There are a variety of theories which have been
put forward.
• The theories are:
– Cosmic particles bombarding the atmosphere from space
– Dust particles rubbing against each other
– Large particle, small particle updraft theory (ICE)
– Electro-release condensation theory
Cosmic Particle Theory
• Some scientists suggest lightning is
the result of cosmic particles coming
from space
• Least respected/documented theory
If this were the case, why don’t we see an
increase in the frequency of lightning at
solar maximum, a decrease at solar
minimum, or just an overall fluctuation in
lightning frequencies?
Dust Particle Theory
Some scientists suggest that dust particles
from volcanic eruptions, forest fires or
human induced pollution create this potential
for lightning, by bumping into each other
then separating the charged particles.
If this were the case we would be able to see
a marked increase in storm intensities when
dust particles interacted with cloud nuclei.
But dust particles do influence the type of
lightning as discussed later concerning
positive cloud to ground strikes.
Ice Theory
•
The most accepted view of how charge separation occurs…but not
necessarily right.
•
Water cycle. Clouds can suspend millions of water/ice particles.
•
Collisions with other particles due to evaporation/condensation.
•
Electrons knocked off rising moisture - Collect at the bottom as positive
moisture particles rise above them by strong updrafts
•
As moisture particles get higher, begin to freeze – giving them negative
charge and then fall back down to earth.
•
The problem with this is that storms that contain no ice still produce
lightning so their must be something else going on which explains why
lightning occurs, although it still has to do with the water cycle.
Electro – Release Condensation
• NASA has shown that there is a correlation between the
volume of rain in a storm and the amount of lightning.
• Although not established fact, it does fit the parameters
for lightning.
• The theory is based on the Mills Law of Electron Transfer
Via Matter State Changes.
Mills Law of Electron Transfer Via Matter
State Changes
• States that when matter changes states, there will be a
corresponding transfer of electrons.
• Predicts condensing areas have negative areas or surplus of
electrons.
• Dissipating parts due to evaporation will have positive charge and
loss of electrons.
• Freezing/thawing.
• Volume + rapidity of condensation determines the amount of
lightning produced.
The Chemistry Of This
• Water molecules in liquid state share electrons
covalently enabling H2O molecules to exist at a lower
energy level, the factor making them behave as a liquid.
• H2Oliq + heat locks up e- in complete outer sub shell.
• Molecule now free to act as a gas & refuses to share
electrons, leaving behind fewer electrons to be shared
by the rest of liquid water.
The Chemistry Continued.
• As the gas H2O lose heat energy, also lose ability to
maintain full outer shell of e-
• Gas molecules forced to condense with each other,
sharing e• Giving up surplus of heat & e- can no longer afford to
hold.
• If condensation occurs quick + sufficient enough, a
lightning storm will ensue.
Evidence For The Theory
• Research by two separate teams, Studwell and Orville (1995) and
Holle and Watson, (1996) discovered a majority of positive flashes,
in areas of freezing rain. As water freezes it becomes negatively
charged. Since freezing rain becomes frozen on contact with the
ground, it imparts a negative charge to the ground on freezing. Any
discharge would be a positive flash!
• Laboratory experiments directed by E J Workman at the New
Mexico Institute of mining and technology back up the freezing rain
theory by showing that when dilute solutions of water are frozen, a
large electric potential develops between the water and the ice. The
experiments show that the ice gains a negative charge while the
water retains a positive charge. Again exactly what the theory of
Electron Transfer Via Matter State Change predicts.
Summary
• Expect more storms on the plains + southern states of
U.S where potential for large amounts of moisture can
rise to great heights and cooled quickly, hot & cool air
collide.
• NW U.S and Canada plenty of moisture but not warm
enough, so condensation has chance to bleed off
resulting in drizzle with few storms.
• Explains all the observable results shown by
experiments
Houston, Lightning Capital of
Texas
• 12 year study by Texas A&M concluded that
lightning strikes Houston more than anywhere
else.
• 4-5 million people in area plus 50% petroleum
refineries in U.S create massive heat island.
• Results in increased cumulous clouds formation
and more intense storms.
• 1.6 million cloud-to-ground flashes with 75%
during summer
Other Facts from Houston
• Air pollution considered a factor relating to lightning
frequency. Affecting the mix of water and ice in a
thunderstorm which affects the charging process.
• Also aerosols from urban areas may increase the flash
density which has been observed in Houston area.
Florida Scientist’s Research
• According to Joseph Dwyer, physics Prof. at Florida tech. conditions
we thought necessary for lightning do not occur in nature.
• For generations we thought that the electric fields must be
enormous to create such a charge.
• Scientists have been searching for these for years but come up
empty handed.
• Not looking hard enough? No just don’t exist.
• New limit in nature, like water in a bucket, stunted by gamma rays
and anti-matter positrons.
Lightning and Tornadoes?
•
When scientists from a dozen universities + instruments took to a corn field
on the Kansas/Colorado border they came up with some surprising results.
•
Most importantly, researchers witnessed several events within storms that
seemed to predict when tornadoes form. They noticed several updraft areas
where lightning would suddenly cease, then seconds later, a tornado would
form.
•
Importance of this is better prediction by weather-forecasters for severe
weather. Use of instruments to collect data on positive strikes - special radar
stations
• Apart from their results on positive cloud to ground strikes which I
will discuss in a minute they found new clues which might explain
strange lights observed in upper atmosphere above clouds called
red sprites, blue jets, trolls and elves.
A Sprite can exceed 10 million meters a second
• Sprites which can be
seen by naked eye are
glowing ribbons which rise high
above blue jets, last for 3-10 milli.
secs. But they only occur over
positive cloud to ground strikes.
Blue Jets
• Blue jets are extremely energetic fields of charged
particles that rise up to 30 miles from the tops of clouds.
After they occur, lightning stops for several seconds.
• These are very rare and not much
is known about them but they can
reach speeds of 100,000 metres
a second.
Positive Cloud to Ground
Strikes
•
In a positive-to-ground lightning strike, positive charges first rush from the
cloud to the ground, creating a lightning channel through which electrons
flow from the ground back up to the cloud. Such lightning strikes tend to
carry more charge, last tens of seconds longer and be less branched than
the more common negative-to-ground lightning.
•
The presence of smoke, dust, or pollution seems to encourage the
development of positive flashes. This is probably because of the particles'
effect on the number and sizes of ice crystals within storms. A study in the
journal Science (10/2/98) examined thunderstorms in the Southern Plains
during the spring of 1998, when smoke from Mexican forest fires was
flowing northward over the region. Up to three times the usual number of
positive flashes were observed in these smoke-altered storms.
Pavel Jungwirth Paper
• Too much info but basically their work was on how different compounds
affect the polarity of lightning strikes.
• Under normal conditions, when sulfates dominate as cloud condensation
nuclei, this ionic mechanism is consistent with the prevailing negative
lightning in thunderstorms. But with the decrease of sulfate anions, the
present mechanism predicts a shift towards positive charging. This fits
well to a large range of observations of enhanced positive lightning,
connected with smoke, rich in chlorides and nitrates, that could not be
previously explained.
• Performed tens of such collision simulations, have always observed
transfer of several to several tens of water molecules, 1-8 ammonium
cations, and 0-3 sulfate dianions from the graupel (snowflake crystals
falling through very moist air) to the ice crystal. In all cases, the number
of transferred ammonium cations was larger than twice the number of
sulfate dianions. Consequently, these collisions led to positive charging of
the ice crystal (and negative charging of the graupel).
Links to Aerosols and Forest Fires
• Under certain atmospheric conditions (biomass burning
or forest fires) a large amount of aerosols containing
other soluble ions, such as potassium cations and
chloride and nitrate anions are released into the
atmosphere.
• The present simulations indicate that replacing the
sulfate dianion with monovalent anions such as chloride
or nitrate leads to an opposite polarity of charging during
graupel-ice crystal collisions, due to the change in the
salt solution covering the graupel.
• The fires in the south of Mexico in 1998 accumulated for a tripling of
positive lightning over the U.S. The median peak current was
increased by over 20 kA. Chemical analysis of the smoke that
reached the USA, showed that the fraction of nitrate and organic
anions was greater than in the ambient aerosols.
• A very clear signal was also obtained from cumulimbus clouds fed
directly from forest fires in the USA and Canada. Latham (1991)
documented that a large prescribed fire in Canada caused a
pyrocumulus storm that had produced exclusively 21 positive cloud to
ground flashes, whereas other thunderclouds in the vicinity that did
not ingest the smoke produced tens of “normal” negative flashes.
• Canadian scientists suggested positive lightning was responsible for
the fires because of their higher energy and they persist longer.
Positive feedback loop.
NASA Discoveries
• Lightning prefers afternoons, believed due to the
land absorbing heat and causing strong
convection.
• Patterns change each year, tremendous
variations outside the tropics. As summer
progresses in N Hemis. Lightning moves further
north.
• Strong updrafts which cause lightning relate to
stronger storms, predictions on type of storm.
• C-C lightning more energetic than C-G more
likely to produce violent storms.
This map depicts the ratio of cloud-to-cloud lightning to cloud-to-ground lightning
over U.S. The red areas show where the ratio is as high as 10 cloud-to-cloud
strikes for every ground strike. Blue areas indicate ratios as low as 1:1. red
predicted to be more energetic/violent
Benefits of Lightning
• This last section is something I found that
links lightning strikes to health, but in a
good way.
• After a storm, the air feels clean and fresh,
filled with negative ions. In a thunderstorm,
positive ions precede a strike, followed by
negative ions after it.
• The air we breathe contains both + & - ions, a lack of or imbalance
of these ions has been proven to affect us and our environment.
• Research shows that most of us who live, work and travel in closed
spaces suffer some degree of negative ion starvation or positive ion
overabundance. This has become extremely evident to NASA in
their space travel program.
• In cities like New York, Los Angeles, Hong Kong, Tokyo and Mexico
City and many densely populated cities, there may be few or no
detectable negative ions at all during heavy traffic and high pollution
periods.
Winds of Depression
• The natural production of ions may result from solar or cosmic
radiation or the more mundane friction between air masses such as
between rapidly moving hot, dry air and the ground. These are the
"Witches Winds" that cause such discomfort periodically to the
population in certain areas of the world.
• In these areas, the seasonal winds have become legendary,
bringing misery and chaos to many of the local people. In these
places it has been known for generations, that the winds bring
feelings of anxiety, stress, depression and sleepless nights.
• Statistics show that when they blow, more road accidents happen
and suicide rates increase.
• So real is the problem that it has been known for judges to take this
into consideration when sentencing, and for hospitals to postpone
some operations until the winds cease!
The Ion Effect
• There are some amazing clues to how an excess of
positive ions and a lack of negative ions can produce
uncomfortable effects, Studied by the Dr. Albert Krueger,
Professor Emeritus of the University of California at
Berkeley.
• Dr. Krueger demonstrated that small air ions are
biologically active and can stimulate the over-production
of the powerful neurotransmitter serotonin. Serotonin is a
very active neurohormone causing profound nerve,
glandular and digestive effects throughout the body.
• Negative ions can provide major benefits for asthma,
chronic fatigue syndrome, hay fever, allergies, sleep &
snoring, depression, sinus, migraines, colds & flu,
nausea, chemical sensitivity, cigarette smoke & other
odors, computers & office pollution.
• The earth's atmosphere is absolutely full of ions. Nature
was making them even before life began.
• Western scientists believe that ionization, in the form of
lightning, was probably instrumental in the formation of
amino acids - essential components for the beginnings of
life!
Conclusions / What I have learnt
• Non sulfate particles affect the amount of
+ive lightning strikes.
• Sprites + Jets
• Links to tornado/weather prediction
• Limitations of electric field size in the
atmosphere.
• Urban heat affect, increases convection of
cool air with warm air.