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Lightning | SciByte 9

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This week on SciByte we take a look at lightning, what it is, how it works, the facts about it and see if some lightning myths and rumors are indeed close enough for science. We also take a look at a few of the wilder things lightning can do.

All that and more, on SciByte!

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Show Notes:

Disclaimer
  • Science does NOT currently know what exactly guides a lightning bolts path, or why it strikes in one place and not another. So we won’t be able to give you ALL the answers of lightning, but we do hope to give you a better idea of what’s going on and where it can happen.
People have pondered over lightning though out time
  • The Greeks both marveled and feared lightning as it was hurled by Zeus.
  • The Vikings, lightning was produced by Thor as his hammer struck an anvil while riding his chariot across the clouds.
  • The Aztecs also portrayed Lightning as a supernatural power of the god Tlaloc.
So what is lightning?
  • Lightning is an atmospheric electrostatic discharge (spark) accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions, forest fires, or dust storms if there is sufficient dust in the air to provide a static charge.
Rocket lightning
  • Lightning that has been triggered by launching lightning rockets carrying spools of wire into thunderstorms. The wire unwinds as the rocket ascends, providing a path for lightning. These bolts are typically very straight due to the path created by the wire.
What kind of lightning is there?
  • There is cloud-to-ground, ground-to-cloud, cloud-to-cloud, bead lightning, ribbon lightning, staccato lightning, forked lightning, sheet lightning, heat lightning, dry lightning, rocket lightning, positive lightning, ball lightning, volcanic lightning, lightning in a snow storm, red sprite, Elves, blue jet and even extraterrestrial lightning. [PIC - Types of Lightning]
What are the basics of thunderstorm formation?
  • AKA : electrical storm, lightning storm, thundershower, or simply a storm
  • A form of weather characterized by the presence of lightning and its acoustic effect on the Earth’s atmosphere known as thunder.
  • Thunderstorms result from the rapid upward movement of warm, moist air.
  • As the warm, moist air moves upward, it cools, condenses, and forms cumulonimbus clouds that can reach heights of over 12mi / 20 km. [PIC - Cumulonimbus Cloud
    ]
    [PIC - Cumulonimbus Cloud]
  • As the rising air reaches its dew point, water droplets and ice form and begin falling the long distance through the clouds towards the Earth’s surface.
    • Dew Point : the temperature at which the air can no longer hold all of its water vapor, and some of the water vapor must condense into liquid water
  • The falling droplets create a downdraft of air that spreads out at the Earth’s surface and causes strong winds associated with thunderstorms.
How does lightning initially form?
  • How lightning initially forms is still a matter of debate…
  • We do know that electrical charges build up withing thunderclouds, but there is no single theory that fully describes why.
    • One commonly discussed theory suggests that small cloud particles acquire a positive charge, while other larger particles become negatively charged. These particles eventually separate, and the upper part of the cloud becomes positively charged, while the lower part becomes negatively charged. [VIDEO]
What happens in cloud to ground lightning?
  • The path is first created by a trickle of electricity that rushes outward from a charged region high inside the cloud.
  • It begins as a small spark inside the cloud 5mi / 8km up
  • A spurt of electrons rushes outward travels 328ft / 100 m then stops and pools for a few millionths of a second, then the stream moves off in a different direction, pools again and again.
  • Often the stream branches and splits, this is not a lightning bolt yet it’s called a stepped leader, an intensely charged channel leaping and branching down.[VIDEO]
  • As it gets close, about 33-330ft / 10-100m, its electric field begins to exert a pull on the ground.
  • The ground is now ‘aware’ of a large surplus of negative electricity coming down on a conductor, certain objects on the Earth respond by launching little streamers, weakly luminous plasma filaments which are trying to connect with whats coming down.
  • It’s the positive streamer that makes the connection that gives rise to the return stroke and only exist for a minute fraction of a second.
  • The electrons can now drain to Earth, the part of the channel closest to Earth will drain first, then successively higher parts all the way to the charge in the cloud.
  • The visible lightning bolt flows up as the massive electric currents flow down.
So what IS lightning doing?
  • Lightning causes ionisation in the air through which it travels
    • Ionization is the physical process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or other ions
How much power does a lightning bolt pack?
  • The voltage for any given ‘bolt’ is proportional to the length of the bolt
  • The average single lightning stroke is about 3.9 times the largest man-made voltage
    • Lightning bolt ~ 100 million volts = ~ 100,000,000 V
    • Largest man made voltage ~ 25.5 million volts = 25,500,000 V
  • The average peak power output of a single lightning stroke is about one trillion watts — one 1 terawatt = 1,000,000,000,000 W
    • Power of 1 lightning bolt = 7,142 x Power of Boeing 747 (140MW)
    • Power of 1 lightning bolt = 826 x power required to send a DeLorean traveling at 88 mph from 1955 to 1985 (1.21GW)
    • Power of 15 lightning bolts = average total power consumption of the human world in 2004 (15TW)
    • Power of 44 lightning bolts = average total heat flux from earth’s interior (44TW)
  • All of this happens in about 30 millionths of a second 30 millionths of a sec = 0.00030 sec
Extraterrestrial lightning.
  • Lightning has been observed within the atmospheres of other planets, such as Venus, Jupiter and Saturn.
  • Venus : Lightning on Venus is still a controversial subject after decades of study.
    • During Soviet and U.S. missions ing the 70-80’s, signals suggesting lightning may be present in the upper atmosphere were detected..
    • However, recently the Cassini–Huygens mission fly-by of Venus detected no signs of lightning at all.
    • Despite this, it has been suggested that radio pulses recorded by the spacecraft Venus Express may originate from lightning on Venus
  • Jupiter : The electrical discharges on Jupiter can be up to a thousand times as powerful as lightning on the Earth [PIC - Jupiter Lightning] [PIC - Jupiter Lightning]
  • Saturn : Since early 2005, scientists have been tracking lightning on Saturn. The power of the lightning is approximately 1000 times that of lightning on Earth. [PIC - Saturn lightning]
What temperatures can lightning and/or the air surrounding it get to?
  • It can heat the air immediately surrounding it to about 3.5 times the surface of the Sun
    • Air surrounding lightning heated to about 36,000 F / 20,000 C
    • Sun’s surface temperature ~ 9941 F / 5505 C
  • Lightning itself is over 5 times hotter than the surface of the Sun!
    • Lightning temperature around 54,000 F / 30,000 C
Wait … hotter than the surface of the Sun? … how come we’re not burned up?
  • It isn’t the Sun’s temperature, however, that accounts for the heat we feel on Earth. Rather, it’s the Sun’s size.
  • The Sun has a surface area a 100 million billion times the surface area of a typical lightning bolt. 100 million billion = 100,000,000,000,000,000
  • Earth gets about a 100 million times more energy from the Sun than from a lightning bolt over the same time period.
How Fast does lightning travel?
  • NOTE investigating this we ran across conflicting data. Some of this seems to be due to the km vs miles issue, but also because various steps in the lightning process travel at different rates!
  • Leaders could travel around the equator of the Earth in about 11 min
    • Leader can travels at ~ 136,000 mph / 219,000 km/h
    • Earth equator : 24,901 mi / 40,075 km
    • 136,000 mph * [ 1hr / 60 min ] = 2266.7 mpm
    • 24,901 mi / [ 2266.7 mi / min ] ~= 11min
  • Return Stroke could travel around the equator of the Earth in about 1.4 sec
    • Return Stroke can move at over 62million mph / 100million km/hr
    • Speed of Light : 671 million mph / 1.02 billion km/hr
    • Earth equator : 24,901 mi / 40,075 km
    • 62,000,000 mph * [ 1hr / 3600 sec ] = 17,222 mps
    • 24,901 mi / [ 17,222 mps ] ~= 1.4 sec
How does lightning produce thunder?
  • Thunder is the shockwave radiating away from the strike path.
  • When the air heats up, it expands rapidly, creating a compression wave that propagates through the surrounding air.
  • This compression wave manifests itself in the form of a sound wave.
How can I tell how far away a lightning bolt is?
  • Count the seconds between the flash and the thunder, then take that number and divide by 5 to get the distance in miles, or by 3 to get kilometers. [PIC]
    • [ Seconds between flash and thunder ] / 5 = miles
    • [ Seconds between flash and thunder ] / 3 = kilometers
    • On a standard day at sea level the speed of sound is about ~ 760 mph /1223km/h
    • Light travels at a constant ~ 186,000 mps / 299,337 km/s
Positive lightning
  • Positive lightning makes up less than 5% of all lightning strikes and occurs when a positive charge is carried by the top of the clouds (generally anvil clouds) rather than the ground.
  • This usually causes the leader arc to form in the top of the cumulonimbus cloud and travel horizontally for several miles before turning towards the ground to meet a negatively charges streamer rising from the ground. [VIDEO - Positive Lightning]
  • AKA Ground to Cloud Lightning
Ground to Cloud Lightning
  • AKA Positive Lightning
  • Ground-to-cloud lightning is a lightning discharge between the ground and a cumulonimbus cloud initiated by an upward-moving leader stroke.
Heat lightning
  • Heat lightning is a common name for a lightning flash that appears to produce no thunder because it occurs too far away for the thunder to be heard. The sound waves dissipate before they reach the observer.
Dry lightning
  • A term in Canada and the United States for lightning that occurs with no precipitation at the surface and is the most common natural cause of wildfires.
  • Includes sandstorms [VIDEO - Sandstorm Lightning]
Volcanic lightning
  • AKA : A dirty thunderstorm is a weather phenomenon that occurs when lightning is produced in a volcanic plume. [PIC : Volcanic Lightning] [PIC : Volcanic Lightning]
  • Extremely large volcanic eruptions, which eject gases and material high into the atmosphere, can trigger lightning.[PIC : Volcanic Lightning]
  • An intermediate type which comes from a volcano’s vents, sometimes 1.8 mi / 2.9 km long.
  • Small spark-type lightning about 3 ft / 0.91 m long lasting a few milliseconds.
Ball lightning
  • Ball lightning is a hypothetical atmospheric electrical phenomenon, of which little is known.
  • Usually described as a floating, illuminated ball that occurs during thunderstorms and lasts considerably longer than the split-second flash of a lightning bolt some have been known to pass through windows and even dissipate with a bang.
  • Given inconsistencies and the lack of reliable data, completely contradicting and unpredictable behavior, that that it has rarely, if ever, recorded by meteorologists the true nature of ball lightning is still unknown and was often regarded as a fantasy or a hoax until recently.
  • Several theories have been advanced to describe ball lightning, with none being universally accepted.
  • Ball lightning Theories include :
    • Vaporized silicon hypothesis – Lightning striking Earth’s soil could vaporize the silica contained within it, turning it into pure silicon vapor. As it cools, the silicon could condense into a floating aerosol, bound by its charge, glowing due to the heat of silicon recombining with oxygen.
    • Aerodynamic vortex is cut causing it to shrink into a sphere hypothesis – lightning perpendicular to the ground would couse thunder shock waves that could form a horizontal vortec, would would rotate under pressure
    • Nanobattery hypothesis – composite nano or submicrometre particles, each particle constituting a battery. A surface discharge shorts these batteries, resulting in a current which forms the ball
    • Black hole hypothesis – the passage of microscopic primordial black holes through the Earth’s atmosphere. This theory was inspired by an account of ball lightning in 1868, in Ireland that lasted 20 minutes and left a 19.6ft / 6m square hole, a 295ft / 90m long trench, a second trench 82ft / 25m long
    • Buoyant Plasma Hypothesis – a declassified report concluded that buoyant charged plasma formations similar to ball lightning are formed by novel physical, electrical, and magnetic phenomena. Why they would appear in nature in not fully understood, but one theory includes meteors breaking up in the atmosphere and forming charged plasmas
    • Transcranial magnetic stimulation – hallucinations experienced by patients having epileptic seizures in the occipital lobe are similar to the observed features of ball lightning.
Breaking down a few lightning myths / rumors
  • Do rubber soled shoes or tires protect me? No. Rubber-soled shoes and rubber tires provide no protection from lightning. However, the steel frame of a hard-topped vehicle provides increased protection if you are not touching the cars metal.
    • Although you may still be injured if lightning strikes your car, the metal frame of the care will act kind of like a Faraday cage so you are much safer inside that unprotected outside.
    • Faraday cage : an enclosure formed by conducting material or by a mesh of such material that blocks out external non-static electric fields. [VIDEO - Faraday Cage]
  • Does lightning always hit the tallest object around? No. The tallest objects in a storm don’t always get struck by lightning, while it is true that they have a higher possibility of a strike, strike paths are not currently predictable.
  • I’ve heard that you should avoid taking a shower/doing dishes during a storm… If lightning strikes the ground near you home the electrical discharge can travel up water pipes, so if you want to play it safe it’s a good idea to stay away from water pipes as well.
    • This threat is not as great as it used to be, because PVC (polyvinyl chloride) is often used for indoor plumbing these days. If you are not sure what your pipes are made of or if you live in an older home, really anything built before 1980 would be suspect, wait it out.
  • Does talking on the phone during a storm pose a danger? Talking on a land line poses a danger of injury or death if the lightning strikes the phone line and the electrical discharge travels up the lines to your handset. If you are using a cell phone or cordless phone indoors during a storm you are relatively safe because there is no wire for the discharge to travel down.
  • Do I have to unplug my surge protectors? Surge protectors are there to provide protection for power surges from the power company; they WILL NOT save your electronics if lightning strikes your power line.
  • The storm isn’t overhead I’m safe right? No. Lightning often strikes outside of heavy rain and may occur as far as 10 miles away from any rainfall.
    • The US Federal Emergency Management Agency (FEMA) actually suggests following the 30/30 rule. “Go indoors if, after seeing lightning, you cannot count to 30 before hearing thunder. Stay indoors for 30 minutes after hearing the last clap of thunder.”
Quick Facts
  • 16 million lightning storms in the world every year
    *Some places on Earth get more lightning that others Lightning ‘density’ map
  • It is estimated that somewhere on the Earth there are about 45 lightning flashes per second for a total of 1.4 billion per year only about 1/4 to 1/3 of which are cloud-to-ground. [VIDEO - Lightning from Space]
  • The irrational fear of lightning (and thunder) is astraphobia.
  • Lightning causes ionisation in the air through which it travels, leading to the formation of nitric oxide and ultimately, nitric acid, of benefit to plant life below.
Cloud-to-Cloud Lightning
  • AKA Sheet Lightning
  • Intra-cloud Lightning This occurs between oppositely charged centers 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.
  • Inter-cloud lightning This occurs between charge centers in two different clouds with the discharge bridging a gap of clear air between them.
Sheet lightning
  • AKA Cloud-to-Cloud, intra-cloud, or inter-cloud lightning
  • Sheet lightning is an informally applied name to cloud-to-cloud lightning that exhibits a diffuse brightening of the surface of a cloud caused by the actual discharge path being hidden or when the lightning itself cannot be seen, so that it appears as only a flash, or a sheet of light.
Thundersnow? … so there is lightning in a snow storm too?
  • Thundersnow is a relatively rare kind of thunderstorm with snow falling as the primary precipitation instead of rain; although is it more common with lake effect snow in the Great Lakes area of the United States and Canada, the midwestern U.S., and the Great Salt Lake. [VIDEO - thundersnow]
  • One interesting thing is that the snowfall acts as an acoustic suppressor of the thunder, and can usually only be heard within a two to three mile radius from the lightning.
    • In the United States, March is their peak month of formation, and on average, only 6.3 events are reported per year.
Bead lightning
  • Bead lightning is relatively rare is a type of cloud-to-ground lightning which appears to break up into a string of short, bright sections, which last longer than the usual discharge channel. PIC
    • Theory : the observer sees portions of the lightning channel end on, and that these portions appear especially bright
    • Theory : the width of the lightning channel varies; as the lightning channel cools and fades, the wider sections cool more slowly and remain visible longer, appearing as a string of beads
Ribbon lightning
  • Ribbon lightning occurs in thunderstorms with high cross winds and multiple return strokes. The wind will blow each successive return stroke slightly to one side of the previous return stroke, causing a ribbon effect. [PIC - Ribbon Lightning] [PIC - Ribbon Lightning]
Staccato lightning
  • Staccato lightning is a cloud to ground lightning strike which is a short-duration stroke that appears as a single very bright flash and often has considerable branching. [VIDEO - Staccato]
Forked lightning
  • Forked lightning is a name, not in formal usage, for cloud-to-ground lightning that exhibits branching of its path.
Red sprite
  • Sprites are large-scale electrical discharges that occur high above a thunderstorm cloud, or cumulonimbus, giving rise to a quite varied range of visual shapes. [PIC - Red Sprite] [PIC - Red Sprite]
  • They are triggered by the discharges of positive lightning between the thundercloud and the ground and appear as luminous reddish-orange flashes. They often occur in clusters within the altitude range 30-55 mi / 50–90 km above the Earth’s surface.
  • Sprites are cold plasma phenomena that lack the hot channel temperatures of tropospheric lightning, so they are more akin to fluorescent tube discharges than to lightning discharges.
  • Nobel laureate C. T. R. Wilson had suggested in 1925, on theoretical grounds, that electrical breakdown could occur in the upper atmosphere, and in 1956 witnessed what possibly could have been a sprite.
Elves
  • Emissions of Light and Very low frequency perturbations from Electromagnetic pulse Sources
  • This refers to the process by which the light is generated; the excitation of nitrogen molecules due to electron collisions (the electrons possibly having been energized by the electromagnetic pulse caused by a discharge from the Ionosphere).
  • Elves were first recorded on another shuttle mission, this time recorded off French Guiana on October 7, 1990.
  • Elves often appear as dim, flattened, expanding glows around 250 mi / 400 km in diameter that last for, typically, just one millisecond that occur in the ionosphere 60 mi / 97 km above the ground over thunderstorms.
Blue jet
  • Blue jets differ from sprites in that they project from the top of the cumulonimbus above a thunderstorm, typically in a narrow cone, to the lowest levels of the ionosphere 25-50 mi / 40-80 km above the earth. [PIC - Blue Jet]
  • They were first recorded on October 21, 1989, on a video taken from the space shuttle as it passed over Australia, and subsequently extensively documented in 1994 during aircraft research flights by the University of Alaska.
Gigantic Jet
  • Discovered in 2007 [VIDEO - Gigantic Jet]
  • Similar to Blue Jets and red sprites
  • Although the complete mechanics are unknown it is clear that the jets reduce charge imbalance between different parts of Earth’s atmosphere.
  • Gigantic jet, traversed perhaps 70 km/s
What are some of the crazy things lightning can do … ?
  • Lightning can instantly evaporate tree sap, and can cause the tree to ‘explode’ causing bark and pieces of tree to travel out at lethal speeds. [PIC - Evaporate Tree Sap]

What CAN you do if you are …

  • in a forest … Seek shelter in a low area under a thick growth of small trees.
  • in an open area …Go to a low place such as a ravine or valley, but be alert for flash floods.
  • on open water …Get to land and find shelter immediately.
  • anywhere your hair stands on end … Squat low to the ground on the balls of your feet. Place your hands over your ears and your head between your knees. Make yourself the smallest target possible and minimize your contact it the ground. DO NOT lie flat on the ground.
Who has been struck by lightning the most times and survived?
  • Roy Sullivan, a U.S. park ranger in Virginia is recognized by Guinness World Records as the person struck by lightning more recorded times than any other human being. He was hit by lightning on seven different occasions between 1942 and 1977 and survived all of them.
If you or someone else IS struck remember …
  • Metallic devices and wires ( such as iPod/cell phone ) can act as conductors, disrupting flashover and can result in internal injury with a greater risk of dying.
    • Flashover : The high resistance of human skin usually results in lightning being conducted over the skin rather than through the body
  • Lightning strike victims carry no electrical charge and should be attended to immediately.
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