Battle of the Epic Whirlwinds: Hurricane Vs. Tornado

Earth Satellite Space

Versus

Destructive Powerful Tornado

In the Free State of South Africa, 2012 was a year marked by an outbreak of severe thunderstorms. This province lies quite far inland of the subcontinent, to the northeast of Cape Town and to the west of the Drakensberg; the magnificent mountain chain that borders the eastern coastline of South Africa. These severe thunderstorms caused quite a bit of grief for the inhabitants of the Free State, levelling 55 houses and hospitalising 5 people, according to All Africa online publication. But in addition to the heavy rains, lightning and wind damage, these thunderstorms had the ill-grace to drop a couple of tornadoes too!

To put things into perspective, South Africa is not a country known for tornadoes. If you’re thinking of tornadoes, your imaginative context is probably located in the aptly named ‘Tornado Alley’ in the mid-western states of America. Now, as someone who has a degree in atmospheric science, you can imagine how many questions I was fielding from people who had heard about the severe weather events I just mentioned. Not questions as such: statements rather. People rarely ask me questions about the weather. I think they’re afraid of the answers. I can handle that… but what I couldn’t handle was the fact that people were confusing hurricanes with tornadoes!

“Did you hear about the hurricanes in the Free State?”

Portrait of young woman slapping hand on head having a duh momen

To anyone in atmospheric, Earth, ocean or any related sciences – regardless of your specialization – confusing tornadoes with hurricanes is like confusing your grandmother with Megan Fox. It’s like confusing an elephant with a pineapple. The concept of a hurricane tearing across the Free State is about as alien to the weather educated as a giraffe cavorting around the North Pole. Wearing snow shoes.

But, before you cringe at the memory of you making this rather Herculean error, one must take into account that the majority of you out there aren’t weather educated. That’s perfectly all right! We’re going to change that right now. Hurricanes and tornadoes: what’s the difference? Moreover, what’s the big deal if you get them confused? Well, when it comes to these two somewhat (ok, VERY) tempestuous weather phenomena, size really, really, REALLY…

… really, REALLY, really, REALLY, REEEEEEEEALLY does count.

Hurricanes: Kicking Ass and Taking Names

Hurricane Fran satellite image

Satellites captured this fairly terrifying image of Hurricane Fran hurtling towards North Carolina on the 5th September 1996. “Fran” caused so much trouble that they decided to NEVER call another hurricane “Fran” again. 

FYI, hurricanes are named alphabetically according to their order of development during the hurricane season. The first to appear will be named something beginning with an ‘A’, the second ‘B’ and so on and so forth. Hurricane Fran was therefore the 6th fully fledged tropical cyclone to develop that season and one whose limelight was solidly claimed in 2005 by Katrina and again in 2012 by Sandy. Those bitches!

Hurricanes are large tropical storms born over the equator. Fed by prodigious updrafts of hot, moist, sexy air, these giant swirling monsters generate, via condensation alone, 200 times the electrical generating capacity of the entire freaking planet, according to the Atlantic Oceanographic and Meteorological Laboratory. For those of you who like numbers or are easily impressed by them, this equates to 600,000,000,000,000 Watts. This is not even to mention the amount of energy generated by hurricane winds, which is an additional 1,500,000,000,000 Watts of unbridled weather rage!

I don’t even know what that number is… a billion million? A trillion zillion billon million?

Ooh! Aah! Hurricane Statistics

Windy Coast huge waves

  • Damage: Should they make landfall, hurricanes can cause tens of billions of dollars’ worth of damage. Katrina was only a category 3 storm when it had its fender-bender with the Mississippi Gulf Coast. And yet its damage was estimated at $81,000,000,000!
  • Storm Diameter: Hurricanes are huge systems with an average diameter of 800 km (500 mi), although Hurricane Carla, which raged into the Texas coast in 1961, was an especially big girl at 1280 km (800 mi) across.
  • Wind speeds: Hurricanes are wrathful systems with category 5 storms (you do not get larger) generating winds of over 250 km/hr or 156 mi/hr.
  • Associated Severe WeatherHurricanes are social creatures. They have loads of friends they like to bring to the party they tend to gatecrash. These include torrential rainfall, thunderstorms, lightning, hail and storm surges, which is an increase in average sea level that can be in excess of 5 meters or 19 feet! To add insult to grave injury, hurricanes can even generate tornadoes.
  • Weakness: For all their size, energy and capacity for total annihilation, these tropical super storms cannot survive over land. They require a tireless volume of hot, moist air – as is found over the equatorial oceanic regions – in order to preserve storm motion and momentum. That dry continental air just won’t do. Plus, all the friction and turbulence caused by onshore topography (mountains and such) tend to break up the party pretty quickly.

Tornadoes

“Cow…

‘Nother Cow!”

“Actually I think that was the same one”

– ‘Twister’, 1996

I regard tornadoes the same way a sadomasochist regards nipple clamps: they’re deliciously terrifying. Having said this, my opinion is fantastically unfounded because I have never, ever witnessed or had my house relocated by a tornado. If I had, I would probably drop the enthusiasm a notch.

Strong tornado in Kansas

 A Kansas tornado tears across a country roooooad, take me hooooome.

A tornado is a raging column of rotating air that extends from the ground to the base of its parent cumulonimbus cloud, “Cumulonimbus” being the longest and fanciest word everyone remembers from High school geography. I know this because every time I tell someone I have a background in weather, they say, “Oh! So you, like, studied cumulonimbus clouds!”

Yeah, something like that buddy.

Tornadoes are generated by severe thunderstorms in atmospheric environments full of wind shear and abundant lower level moisture, amongst other ingredients. Next time you’re in the bath or swimming pool, make your hand flat, put it in the water and paddle. You’ll notice tiny little vortices or whirlpools that spin off in either direction.

“Wind shear” really just refers to two masses of air moving at different speeds and/or different directions to each other. And, just like your hand in the pool, shear in the atmosphere generates the same kind of ‘whirlpools’ in the air, although you can’t see them because air is invisible. What happens next in tornado genesis is a powerful updraft of air, which pushes these horizontal columns of rotating air vertical. And this is when shit starts getting real.

Severe weather thunderstorm.png

A gorgeous supercell thunderstorm at sunset. This cloud formation, known as a “mesocyclone” to academics and a “mothership” to nerds, is the atmospheric platforms from which tornadoes are commonly spawned.

Ooh! Aah! Tornado Statistics

  • Damage: It just takes one tornado straying into a heavily built up area to rack up damage totals that would bankrupt an entire country. In May of 2011, a single tornado tore through Joplin in Missouri – a city of 50,000 inhabitants. The reports that emerged at the time estimated the damage of insured property alone to be in the region of $3,000,000,000 (billion), and all from a single tornado. This doesn’t even take into account the uninsured losses suffered.

Tornado damage in Lapeer, Michigan.

On the brighter side – Tornado, 1: Insurance companies, 0.

  • Wind Speeds: Tornadoes are violent creatures. The wind speeds that tear around the funnel, more specifically, of F5 tornadoes, have been clocked in at over 500 km/hr or 315 mi/hr. This is more than half the cruising speed of a commercial airliner.
  • Associated Severe Weather: Like hurricanes, tornadoes are social. You will generally find them hanging out with lightning, torrential rain, giant hailstones, wind (duh) and the occasional cow or 18-wheeler semi-trailer.
  • Lifespan: For all their fury, tornadoes are relatively short-lived with the longest ‘twister’ on record having raged on for 3.5 hours. This suspected F5 tornado, dubbed the Tri-State Tornado, tore through 350 km (220 mi) of Illinois, Missouri and Indiana on the 18th March in 1925, leaving almost 700 people dead in its wake.

While hurricanes may boast more impressive size statistics than a single tornado, one should note that the kinds of thunderstorms that generate tornadoes are rarely isolated and often travel in waves with one thunderstorm cell feeding the formation of several others. In 2011, in fact, the National Severe Storm Laboratory recorded the most prolific outbreak of tornadoes in American history! Between April 25th and April 28th 2011, a staggering 358 tornadoes were recorded, with the majority of them having touched down within a single 24-hour period. Thanks to a much more sophisticated weather forecasting and tornado warning system, this outbreak caused half the death toll as the single Tri-state Tornado of 1925.

Class Dismissed: Your Take-Home Message

real airport weather map Hurricane Frances

There are many big and important differences between hurricanes and tornadoes, most of which are related to scale: scale in size, in wind speeds, in damage done and in lifespan. Hurricanes are huge weather systems that last days and can cause widespread destruction. Tornadoes are much, much smaller weather phenomena generated by severe thunderstorms. Yet, in spite of their exponentially smaller size and shorter life spans, they can do incredible localized damage and frequently boast wind speeds greater than even a Category 5 hurricane.

So, to sum it all up and pack it in a nutshell:

Tornadoes can rearrange your back garden and perhaps relocate your house.

Hurricanes can rearrange your province and perhaps the entire eastern coastline of your country.

Real Sprites Caught on Camera!

No, this is not a joke, although I’m not referring to the sprites of fairy tales…

A “sprite” is a whimsical name given to a particularly ephemeral upper atmosphere phenomenon that’s generated by lightning discharges in powerful thunderstorm clouds. Sprites are witnessed as whispy colourful flickering shapes above the thunderstorm clouds and in this video, we watch a team of storm-chasers in hot pursuit of these large-scale electrical discharges.

The things people do for science…

Video Source:Storm Chasing in a Jet – Capturing Upper-atmospheric Lightning” Uploaded by CuriousVideos to YouTube channel www.youtube.com/watch?v=vSCwiQWzMa0.

Original Source: From NOVA – At the Edge of Space by PBS

Shocking Video of Lighting in Slow Motion

This clip from Discovery Channel’s “Raging Planet” shows lightning in super slow motion leave the cloud and connect with the ground. Capturing and watching this footage is helping atmospheric scientists develop a much better understanding of how lightning works. For the rest of us lay folk, it makes for some super interesting visual entertainment!

Video Source: Discovery Channel “Raging Planet” – Lightning. Uploaded by ONE Interpreting on YouTube channel www.youtube.com/watch?v=64WMsNRJvDo

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Enlightening! How Lightning is Made

Lightning thunderstorm picture 

What’s more than ten kilometres (6 miles) long, five times hotter than the surface of an average star and packs in more strokes per second than an over-zealous teenage boy who’s just discovered the joy of internet porn?

Yeah, I know. The picture kind of gives it away doesn’t it?

I have had a complete love affair with thunderstorms for as long as I can remember. I think they are the most awe-inspiring and yet paradoxical demonstration of nature’s prodigious temper and seductive grace. In the space of an hour, the sky can go from an azure blue to the colour of dark slate as giant cumulonimbus clouds broil and swell with latent energy.

Thunderstorms generate all kinds of severe weather: torrential downpours, vicious winds, hail, microbursts and even tornadoes. But they indirectly owe their very name to the one weather feature that claims the lives of, on average, 55 people every year in the United States: lightning!

Shocking Statistics

NASA_Lightning_Climatology

Source: Global distribution of lightning April 1995 – February 2003 from the combined observations of the NASA OTD (4/95-3/00) and LIS (1/98-2/03) instruments.

Approximately 8 million bolts of lightning strike the Earth every single day, starting 10,000 forest fires annually. In the United States, over 300,000 insurance claims are made against lightning damage every year and the bill for this damage is a staggering $400,000,000.

Yes. Thunderstorms are seriously dangerous systems. I shouldn’t have to tell you that and yet countless golfers are killed by lightning every year. Could there be anything less intelligent than standing in the middle of a wide open space during a thunderstorm with a metal rod in your hand pointed at the sky? With five billion joules of energy surging through a single lightning bolt – enough energy to illuminate a 100 watt bulb for three months – you are picking a fight you simply cannot win.

Against all logic, according to the U.S. National Weather Service, lightning STILL kills more people than tornadoes AND hurricanes combined. What is this madness?

It’s Electricity! 

Lightning thunderstorm picture 2

Thunderstorms are extremely busy weather systems. Within a storm cell, legions of water vapour particles are whipped, flung and tumbled around by complex air circulations. Storms themselves are powered by strong updrafts of hot, moist air. This air cools and condenses as it rises through the heights of the lower atmosphere, becoming dense. It consequently loses its upward momentum and sinks and spills out of the rear of the thunderstorm (check out the diagram below).

thunderstorm diagram

Photo Credit: “Thunderstorm formation” by NOAA T-storm-mature-stage.jpg. Licensed under Public Domain via Wikimedia Commons

Together, these motions form a continuous cycle of updrafts and downdrafts, which provides the storm system the energy it needs to electrocute golfers, whip cows into the air and blow Dorothy and her dog, Toto, into a parallel reality.

How does this explain what lightning is? Well, it brings us a lot closer to understanding cloud polarization. OMG. What does that mean?

Clouds Can be Bi-Polar Too

Just like batteries, molecules and certain members of your family, clouds too can become bi-polar. Within a thunderstorm, legions of water vapour particles get swirled around violently by the turbulent air circulations. But there are two predominant movements of air in a single cell storm system: hot moist air going up and colder drier air going down.

The water vapour particles being swept up into the cloud smash into those going down and these collisions, while totally invisible to us, are violent enough to cause the descending water particles to literally tear electrons off of the ascending water particles. Electrons are negative. So you see there is a gradual separation of charge within a thundercloud as the descending water particles become negatively charged and the rising water particles (having had an electron or two pilfered from their orbitals) become positively charged.

cloud polarisation thunderstorm

Credit: Earth Science Australia

As a result of particle motions within a thunderstorm, the lower cloud regions become negatively charged and the upper cloud regions positively charged. A positive charge is induced in the ground immediately below the thunderstorm in response to storm’s electric field.

The story doesn’t end here: the polarization of the thundercloud has an effect on its environment, namely, the surface of the Earth and the various objects on it. An electrical field swells outwards from the cloud, caressing the electrons belonging to Earth’s atoms, seducing them into moving. Those who studied physics will remember, electron movement = charge.

The presence of such a massive reservoir of negative charge immediately above the Earth’s surface repels its negatively charged electrons (like repels like), causing an opposing positive charge to build up. In other words, trees, poles, buildings and your head actually develop a static positive charge in the seconds prior to lightning strike. This is probably why people who have been struck by lightning and have lived to tell the tale say that they felt their hair stand on end just before they become a living conductor for 1,000,000,000 volts of electricity.

Zap!

Lightning thunderstorm picture 4

At some critical juncture, nature notices the thunderstorm’s complete disregard for her love of equilibrium and so a raging streak of electricity discharges between the negative and positively-charged cloud regions. Or the negatively charged lower cloud regions and the positively charged ground immediately below it. And ZAP! You get lightning!

I can feel the cogs of your mind over-heating. So, if you aren’t quite happy with this explanation, then watch the movie Thor. While it doesn’t provide any scientific explanation on lightning genesis whatsoever, Chris Hemsworth is so beautiful you will forget your intellectual torment immediately *swoon*

Guys… you can enjoy watching Natalie Portman at her career low. In a lab coat.

I know I did.

sexy natalie-portman-celebrity

Thunder, Contrary to Kindergarten Mythology, is Not God’s Fart

In spite of my illuminating explanations above – coupled with your homework to watch Thor – the exact physics of lightning generation are not entirely understood. Thunder, on the other hand, is and its explanation makes for a very interesting story. You may want to remember this so you can impress a future date with it…

When lightning tears out of a cloud, the air in the discharge channel heats up from ambient air temperature to a toasty 28,000°C or 50,000°F. That’s approximately five times hotter than the surface of our Sun. And all of this happens in as little as 90 microseconds. I know, right? A yawning chasm of a time denomination.

The problem is, you can’t heat anything up from 10°C to 28,000°C in this short amount of time without some kind of catastrophic consequence. So when lightning shows the ill social etiquette of doing so, the air expands violently, generating a shockwave that explodes outwards from the discharge channel. This shockwave travels faster than the speed of sound – it’s supersonic – so we can’t actually hear it. Dogs probably could, but you’ll have to ask one to be certain.

With distance from the discharge channel, this shockwave slows down and as it does it falls within our audio range. That’s when we hear thunder. I have heard that if you stand close enough to lightning you won’t actually hear it, because the shockwave is supersonic. While this makes sense in theory, human trials are pending. It also explains why, when a storm is very close, the lightning makes a sharp cracking explosive sound while, when further away, you hear the thunder as a low sexy rumble.

Lightning thunderstorm picture 5

Class Dismissed: Your Take-Home Message

More people die of lightning injuries in Florida than anywhere else in America and perhaps even the world. While I’m aware that they have an amazing water world playground at their feet, they also have the highest lightning strike density in the entirety of the United States. Perhaps y’all should bear that in mind the next time you go wind surfing in an electrical storm.

Regardless of where you live, however, if you value your life then don’t swim, don’t bath, don’t chat on a land line, don’t play golf, don’t stand under a tree and don’t go running around like Julie Andrews in a thunderstorm. Otherwise, it won’t just be music the hills are alive with.

Oh, and enjoy the show! Isn’t nature spectacular?

Lightning thunderstorm picture 3

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Run For Cover: Hailstorms on Camera!

Hail is formed by severe thunderstorms and can range in size from super tiny pellets, which sound as though a mouse is tap-dancing on your roof, to massive grapefruits that plough straight THROUGH your roof. In this collection of three videos, we see just how large hailstones give tornadoes a run for their money in terms of the damage they can do.

For a more detailed account of hailstone formation, check out last week’s blog post: Goodness Gracious Great Balls of Ice!

Hailstorm Video # 1

This incredible video clip was filmed – mercifully – from the safety of a residential home. It records the deafening sound of massive hailstones slamming into the roof, as well as into the garden and pool. Note the huge splashes generated by the falling hailstones hitting the water and the size of the stones themselves as they accumulate on the grass.

Insurance companies in Oklahoma must have a very long and convoluted “Terms and Conditions” clause under the “Act of God” claim.

Video Source: “Hail Storm Oklahoma City” Uploaded by Beatlesfanxxl on May 16, 2010, YouTube Channel www.youtube.com/watch?v=OFv2W7Duqiw

Hailstorm Video # 2

Just when you think it can’t get any worse than having large chunks of ice smashing into your roof, porch, pool and garden vegetation, the intensity of the hailstorm swells. Suddenly, it LITERALLY starts raining branches, leaves and torn-up vegetation as this colossal hailstorm shows off its mettle. According to the person who filmed this video, the hailstones ranged in size from peas to baseballs and actually halted traffic on the interstate highways.

Thankfully, the kind of large hail produced by these large thunderstorms tends to fall in narrow swaths and as such, they rarely last longer than a minute in any one area. Still, though, that’s all it takes to leave you with enough yard cleaning to do for weeks!

Video Source: “Incredible Hailstorm Phoenix, Arizona” Uploaded by ChiliDog1723 on October 28, 2010, YouTube Channel www.youtube.com/watch?v=5XeTqp_HRIs

Hailstorm Video # 3

From beginning to end, this amazing hailstorm video shows the incredible damage done by hailstones the size of tennis balls as they smash into Woodson Texas soil, cars and even electrical cables. The guy filming it manages to pick up a couple of the hailstones to show us the size of these monsters in comparison to a quarter (US currency). Towards the end, an ambulance loads a patient who unfortunately got caught in the hailstorm and hopefully only sustained minor injuries. It just goes to show that, in storms the size and strength they are in the American Midwest, not even your car offers you sufficient refuge.

Video Source: “Very Large Hail” uploaded by Cld9trs on November 8, 2006, YouTube channel www.youtube.com/watch?v=wZr8jXo1Uso.

Goodness, Gracious Great Balls of Ice! The Story of Hail

Large hailstone picture

Source: A massive 2.4 inch aggregate hailstone (about 6cm): “Granizo” by nssl0001, National Severe Storms Laboratory (NSSL) Collection. Licensed under Public Domain via Wikimedia Commons.

Some things on our planet are so ridiculous, they could very well be the brainchildren of biblical authors. Frogs falling from the sky, crop circles, giant swirling hurricanes, belching volcanoes, sulphur-based life forms and Paris Hilton’s immense wealth (and equally as immense lack of IQ). And then there’s hail. The fact that the updrafts within a thunderstorm can be strong enough to hold grapefruit-sized hail in suspension is nothing but ridiculous and wholly impressive.

Great balls of ice!

How Hail is Made

Hail consists of balls of ice shockingly called “hailstones”. You may even say that hail is frozen rain, but it deserves a slightly more complex explanation than that…

Hail is made within powerful thunderstorms or cold fronts. Cold fronts tend to produce smaller hail that might inconvenience your dog’s plans to go do his business outside, thereby inconveniencing your plans to keep your house hygienic. The large hail responsible for denting cars, destroying crops and severely upsetting your herd of cows is typically associated with large thunderstorm systems that are well-endowed in the vertical and are sustained by powerful updrafts. These traits are especially exhibited by the “Big Daddy” of all small-scale tempests: supercell thunderstorms. These you will find skipping across “Tornado Alley” during the northern hemisphere’s summer months.

Severe thunderstorm across US Great Plains

Supercell thunderstorm with rotating mesocyclone (*swoon!*). The presence of such large frozen water particles within the cloud selectively reflects light towards the lower energy (green) end of the color spectrum, which is why thunderstorms that produce large hail can make the sky appear a ghostly green.

What cold fronts and thunderstorms have in common is that they are both low pressure systems that suck in air and expel it out their rear. Thunderstorms pull in great volumes of warm and moist air, which rise, cool and condense to form towering cloudy behemoths of cumulonimbus clouds. The air, once cooled, loses its momentum and proceeds to sink towards the ground. Together, these two channels of air comprise the updraft and downdraft zones that sustain a thunderstorm: its lungs if you’ll indulge a bit of poetic licence.

Now, as you should know, temperature decreases with height in the atmosphere. That’s why the tops of high mountains are frozen and it’s why you should always, ALWAYS go for a pee before sky diving. At a certain altitude within a thunderstorm, which can soar to as high as the interface between the troposphere and stratosphere at approximately 10km above sea level, the temperature reaches zero degrees Celsius – the temperature at which water freezes. Above this 0°C isotherm (an obnoxious way of saying “line of equal temperature”) all the water droplets in suspension are frozen.

The strong updrafts within a thunderstorm sweep water droplets above the 0°C isotherm where they freeze (consult the pretty diagram below). These pellets of ice then fall back down towards Earth in the downdraft zone, plummeting below the 0°C isotherm and defrosting into big globs of water. This is why thunderstorm rain gets you soaking wet faster than Channing Tatum’s dirty dancing in “Dirty Mike”.

hail-formation-diagram

Image Source: University of South Florida, scholarcommons.usf.edu

However, some of these falling frozen pellets of rain get caught up in the updraft zone again and are swept back up above the 0°C isotherm. Only, they’ve gained a layer of water, which they collected as condensation while chilling out below the 0°C isotherm. This additional layer of moisture freezes, forming a new layer of ice over the original ice pellet.

Large hailstone concentric circles Concentric layers of ice in a hailstone.

 Image Source: “Hagelkorn mit Anlagerungsschichten” by ERZ – Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons.

This process can repeat itself several times and each time, the hailstone will grow larger and larger and larger as it collects more and more layers of ice. The next time you’re in the middle of a raging supercell storm, run outside, collect a couple of decent-sized hailstones, run back to the tornado shelter, bolt the trapdoor, watch your dad arm wrestle said trapdoor with an F5 tornado, watch your dad lose, resolve to become a hardcore white vest-wearing, tornado chasing sexpot with a serious death wish. Oh! And remember those hailstones you collected? Cut them open to see those concentric circles of icy awesomeness.

When a hailstone finally gets too heavy for the thunderstorm’s updrafts to hold in suspension depends entirely on the strength of those updrafts. The stronger they are, the heavier the hailstones. This is why larger hailstones are associated with powerful thunderstorms, such as the Midwest super cells that are sustained by incredibly strong updraft zones.

And when hailstones get heavy, it’s time to run for cover.

Hailstorm damage

Sorry Boys… Size Really Does Matter

Farmers are more obsessed with size than that clutch of vacuous floozies and jockstraps in Jersey Shore. Considering their livelihood depends on it (and not their egos), this is easy to understand and empathise with. But, in no other aspect are they more obsessed with size than with hail. The happiness and health of their livestock and crops depend on it.

Some thunderstorms can create hailstones that are big enough to cave your head in. Even if you do have brains. The next time you’re at a party, scoop an ice cube out your rum and coke and toss it at your mate (preferably the one who’s hitting on your girlfriend). Listen to the dulcet sounds of squealing as it clobbers him in the noggin. Now imagine something easily ten times the size of that ice cube falling thousands of metres (or feet) from the heavens. Yup! Ouch.

Record_hailstone_Vivian,_SD

Ermagherd! Ferkerng HUGE herlsterne!

 Source: “Record hailstone Vivian, SD” by NWS Aberdeen, SD. Licensed under Public Domain via Wikimedia Commons.

On 23rd June 2010, the largest hailstone in recorded American meteorological history fell in Vivian, South Dakota (image above). This great ball of ice weighed in at 0.88 kg (1.93 lbs) and was a staggering (if it had hit you in the head) 20 cm (8 inches) in diameter.

That’s two inches longer than your average you-know-what, tee hee!

Class Dismissed: Your Take-Home Message

Big Hail Thunderstorm

Hailstones are physical evidence of the incredible air circulations going on inside a thunderstorm. Can you imagine how strong air must be to prevent something that weighs almost a kilogram from succumbing to gravity? I don’t know about you, but that blows my mind in the most delicious way. And so we see that thunderstorms are about so much more than just thunder and lightning and the occasional airborne cow.

The Sky Is Only Sometimes Blue

Beautiful sunrise

If asked what colour Earth’s sky is, you wouldn’t be unforgivably wrong to answer that it’s blue. A more correct answer, however, would be “it’s blue, sometimes”.

Earth’s sky is black at night and grey in overcast weather. It’s brilliant crimson, orange and yellow at sunset, and a sultry blend of indigo, violet and pink at dawn. Around noontime on clear days, it’s white at the horizons and on brooding, stormy days, when there is a promise of severe thunderstorms and hail, it can be slate grey with a slight tinge of green.

The sky is many colours. It’s only sometimes blue. Ever wonder why? Doesn’t matter, I’m going to tell you anyway and what better place to start than by shedding some light on… light!

What Is Light?

Rays of sunshine breaks through the clouds

What we know as light really only represents a fraction of the full spectrum of energy radiated by the sun and the other stars in our Universe (and other possible Universes). Visible light is the narrow range of electromagnetic energy that can be seen by humans and is responsible for illuminating our world in a cacophony of beautiful colour. It’s made up of teensy particles called photons (think photography, meaning “light”), which, unlike gas molecules, don’t float about arbitrarily bumping into the sides of objects like pong balls. Rather, photons travel in waves, just like nausea after some bad Chinese.

Waves are awesome for more than just surfing. They have all sorts of physical properties that, once understood, give us the key to understanding the behaviour of sound and light and our perceptions thereof… such as the colour of the sky!

Like, Wave Properties, Man

Cool surfing goat

Any (serious) surfer will tell you that waves have many properties, including height, amplitude, energy, frequency and wavelength. These are all measurable quantities that can be applied to ALL kinds of waves, including energy and sound waves. For this particular topic, however, we shall be focusing on a property called frequency.

The frequency refers to the number of waves that occur in a given time period. So, imagine you’re sitting on a cliff that faces out to sea. In a period of one minute, you count every wave crest that passes your direct line of sight. The number of crests you count per minute is the frequency. Sounds pretty simple doesn’t it? Now try counting the light waves that are bouncing off your dad’s horrible Hawaiian shirt. Obviously you can’t. We can’t see light waves, or sound waves for that matter, but we CAN perceive the differences that arise as a result of differences in their frequency.

High and low frequency waves

Sound waves with a high frequency (refer to the above diagram with the squiggly lines) are perceived by our ears to be high-pitched. Like the sound your wife makes when she gets mad at you for leaving your cheesy socks next to the bathroom sink. Sound waves with a low frequency are perceived by our ears to be low-pitched, like Barry White’s crooning. Similarly, light that travels at a high frequency is perceived by our eyes to be blue or violet and light with a low frequency, as red or orange. In between, you’ll find green and yellow. Together, they all make up the gay flag!

Visible light spectrum
The above spectrum shows the variation of colour as determined by the frequency of the visible light emitted by the sun (or any star). Violet and blue lie at the extreme high-energy end of the colour spectrum, while red and orange lie at the low-energy end.

As it was initially explained, visible light represents a mere fraction of the full range of energy produced by our star. The “electromagnetic spectrum” may sound like a horribly complex term, but you’ve actually met most of the members of the family! Let’s take a look… Take a deep breath. It’s not complicated. I believe in you!

The Electromagnetic Spectrum

Electromagnetic spectrum

The squiggly line in the middle represents the size of the wavelengths of the various “kinds” of electromagnetic energy, from the low energy radio and microwaves (that you use to heat up your TV dinners) to the high energy X-ray and Gamma rays (that you definitely don’t use to heat up your TV dinners).

Slap bang in the middle of this diagram, you will see the blue box titled “visible”. This is visible light and it refers to a range of energy frequencies that account for all the colours we see and, in general, the light that illuminates our world.

Now, as we move to the right of the spectrum, the waves become more energetic and the frequency increases. Electromagnetic radiation becomes ultraviolet and then X-ray, as is used in medical diagnostic technology to reveal your bony insides. Finally, at the high-frequency end of the electromagnetic spectrum, we get gamma radiation, which is so ridiculously energetic that a minute’s exposure would either incinerate you, or cause such terrible mutation of your cells that you’d turn into Joan Rivers.

Joan Rivers

Thankfully, the gamma radiation produced by the unending nuclear fusion reactions in the heart of the Sun doesn’t quite make it to the Sun’s surface and so, our little planet is safe. Earth’s ozone layer also manages to deflect much of any high-energy radiation that heads our way from other locations in the universe, except for small amounts of UV light, which can cause sunburn and melanoma, amongst other kinds of skin cancers.

But, how on EARTH does this all link back to the colour of the sky?

By understanding how the frequency of visible light determines its position on the colour spectrum, we are given the key to understanding the colour of the sky!

Why Is The Sky (Sometimes) Blue?

animated-blue-sky

When visible light reaches our planet, it encounters all the trillions of molecules of gas, water and other particulates that are so abundant in the atmosphere. While the majority of the spectrum can travel through this veritable obstacle course unscathed, blue light is unlucky enough to be of the perfect wavelength or “size” and so can’t help but collide with all these molecules and particles.

It’s like trying to roll a marble (blue light) tennis ball (green light), skateboard (yellow light), bicycle (orange light) and car (red light) through a car park FULL of marbles. Which one do you think it going to have the greatest difficulty getting from A to B without being deflected off its path? Blue light obviously and as a result, it gets scattered off its original course, which is what we see when we look up at a blue sky. This effect is known as Rayleigh scattering and is named after the obnoxiously titled English physicist, John William Strutt, 3rd Baron Rayleigh Peacock Eminent La-di-da.

In reality, more than just blue light is scattered. A little bit of violet and green and even red light is scattered, too. But it’s predominantly blue that has fender benders across the daytime sky. If you throw a teaspoon of violent, green and red into a bucket of blue paint, the resultant colour will still be blue. This all changes, however, as the sun carves its path across the sky, drawing inexorably closer to the horizon…

Red, Orange and Yellow Sunsets

Beautiful sunset
Sunset over the Satara Rest Camp, Kruger National Park.

From our perspective, the atmosphere at the horizons is thicker owing to the oblique angle at which we are looking at it. The following two diagrams illustrate this point beautifully, saving me a fair amount of wind…

Light entering Earth's atmosphere

Light entering Earth's atmosphere 2

In the first image, the length of the path the sunlight travels to reach the little sunbathing dude, as denoted by the black arrow, is much shorter than in the second image, when the sun sits on the horizon. This longer distance means that by the time the light finally does arrive at the dude’s eyeballs, all the blue light has been scattered out, leaving only the low-energy frequency light: reds, oranges and yellows. This is why sunsets look like sex-on-the-beach cocktails.

It’s also why they inspire cocktails… and sex on the beach.

Interestingly, at midday, the light travelling to us from the horizon still needs to claw its way through a thicker layer of atmosphere. While this light IS scattered red light, its mixture with all the blue scattered light from the rest of the sky causes the one extreme end of the colour spectrum to meet the other, effectively cancelling each other out. The resulting colour is white. In other words, at the horizons, all members of the visible colour spectrum are reunited, leaving you with *drumroll* white light.

Why Are Some Sunsets More Spectacular Than Others?

Beautiful red sunset

Discounting the sunsets you watched while totally baked on that good shit your cousin somehow smuggled in from Canada, the more spectacularly hued sunsets can be attributed to the composition of the atmosphere.

The more particles there are in the sky, be it dust, pollution, smoke, water vapour or the workings of a local volcano with indigestion, the more aggressive the scattering and the more enhanced these effects will be. This explains why there is nothing more beautiful – implications aside – than a sunset over a horribly polluted sky.

Cloudy With A Chance Of Green

Green thunderstorm clouds

There is a strange greenish tinge to the sky that can sometimes develop just before a severe thunderstorm drops its load. It’s especially noted with powerful storms that are able to form large hail and tornadoes. I’ve heard two theories explaining why this happens, but it would seem that the jury is still out on which one is more correct:

  1. Severe thunderstorms typically occur during the latter half of the day and especially towards sunset. These kinds of thunderstorms also form very high cumulonimbus towers and the abundant water vapour within these clouds sends blue light scattering like skittles on a waxed floor. With the sunset throwing red scattered light on the blue underside of the clouds, the resultant visual effect can be a greenish tinge, as you can see in the picture above.
  1. The other explanation is that the presence of large hailstones within a thundercloud can actually scatter light whose frequency is slightly lower than the standard blue. What colour comes next after blue? Green of course, hence the greenish otherworldly tinge. I prefer this explanation since it’s more awesome.

Having said all this, a greenish sky is not a sure-fire indicator that a tornado is on the way, as is a popular myth amongst the residents of Tornado Alley. But it does indicate the presence of a very tall convective storm, which you can pretty much bank on ruffling a few leaves. Maybe even relocating a cow.

Class Dismissed: Your Take-Home Message

Beautiful yellow sunset
Sunrise, somewhere in the middle of the beautiful South African nowhere

The sky appears to us in a myriad of colours throughout the day and it all comes down to the fact that visible light has multiple personality disorder. Whichever colour you do see is a result of that particular frequency of light being scattered more effectively than the others. But our foray into the physics of light has explained more to us than just the hue of the sky… it has also revealed just how many fascinating things wave properties account for, from the pitch of your irate wife’s voice to Indian Ocean tsunamis.

I intend to explore both of these in good time, but in the meanwhile…

What personality is your sky right now?

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