Battle of the Epic Whirlwinds: Hurricane Vs. Tornado

Versus

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?”

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

Satellites captured this fairly terrifying image of Hurricane Fran hurtling towards North Carolina on the 5^th 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 6^th 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

• 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 Weather: Hurricanes 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.

 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.

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.

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 18^th 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 25^th and April 28^th 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

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.

The 2015 "Slushy" Waves of New England

It’s too bad that seawater is salty, because with a bit of sweet flavouring, everyone would have had access to unlimited slushy “Slurpee” a year ago, courtesy of Mother Nature!

Video Source: “Giant Frozen Waves Nantucket Beach” Uploaded by Galaxy 11

The United States spent much of February of last year in the frigid grips of a record-breaking icy winter. Yet, in addition to the usual suspects, which include deep snow and biting winds, the cold would seem to have even won over the briny seawater of the north Atlantic Ocean. This video shows a series of images of ocean waves breaking on the shores of Nantucket in New England (northeast USA), only, there seems to be something distinctly different about these waves!

The photographer, Jonathan Nimerfroh, is an avid surfing enthusiast and on a trip to the beach, he noticed something odd about the horizon. As it turns out, the temperatures are so low in the area the water has begun to freeze and so, what we are looking at are giant slushy waves! These icy waves have also been aptly called “Slurpee waves”

The maximum temperature on the day these pictures were taken was at a teeth-chattering -7 degrees celsius (17 degrees Fahrenheit).

What’s truly amazing about this is that salt is known to lower the freezing point of water to well below zero degrees celsius. This is precisely why we throw salt over our driveways to prevent them from icing up. The fact that even the salty seawater in northeast United States began to freeze is testament to the uncharacteristically cold winter they had last year.

Gird Your Loins, It's El Niño Time!

It took two long haul flights, six plastic wrapped airline meals, three movies, two cantankerous airhostesses and a dangerous brush with halitosis for me to learn about the latest crisis throwing a spanner in the works of the mankind’s (mostly shoddy) attempts to run things smoothly on planet Earth.

I’m talking, of course, about El Niño.

I had to come to Los Angeles to learn that we’re actually teetering on the edge of what the western media is referring to as a “monster El Niño event” and by the time I publish this, we may very well have taken the dive. Where I come from – South Africa – the media and moreover the government pay scant attention to weather and climate issues. This is extremely ironic considering our economy is based on primary industry and that El Niño years are linked with drought in Southern African’s interior. So, in keeping with this relationship, we’re currently facing critical drought conditions for which the government has done nothing to prepare.

Alas! Here in South Africa, the government is far too distracted by President Zuma’s antics in and out of parliament and the country’s courtrooms to worry about the fact that our crops are about to shrivel up faster than Zuma’s manhood when it was explained to him that showering after intercourse does not in fact prevent the transmission of HIV. And unfortunately, they would also rather spend taxpayers’ money on private jets, fancy cars and extravagant lifestyles for its unprecedented number of officials than on research into, and mitigation for climate change and global climate phenomena like El Niño. If you were a selfish, uneducated pack of pricks, wouldn’t you too?

Anyway, that is where my political rant ends. The point is this: I only recently learned that the planet is facing the meanest El Niño event since 1997 and is set to become one of the three strongest on record, like, ever. It’s already causing all kinds of interesting weather anomalies across the world, especially in the United States. So, it’s time for a new blog in which we’ll meet “the boy” wreaking an incredible amount of wanton mischief on our biology, biomes and backyards.

Vainglorious little swine…

Who Is This “Boy” And Why Does He Mischief Thusly?

El Niño refers to the periodic, unusual warming of the ocean waters of the central and eastern equatorial Pacific and it’s named “the boy” in Spanish after the baby Jesus, since it typically occurs around Christmas time. Understanding why El Niño has such extensive impacts upon weather requires us to take a closer look at a very important variable (sea surface temperature) as it usually is versus what it becomes when El Niño buggers around with ocean and atmospheric circulations. And so, the instigator of it all – the key player I need to introduce you to first is…

The Easterly Trade Winds!

 Image Source: mrspruillscience.weebly.com

Over the tropical Pacific Ocean, in other words around the equator, the trade winds blow roughly from east to west (see diagram above). Now, wind may seem like nothing more than moving air until your house gets relocated by a tornado; only then do you realize it’s a force to be reckoned with! So, the effects the northeast and southeast trade winds have on the ocean surface in the equatorial Pacific are quite significant.

The easterlies exert a force on the warm surface water, pushing it and causing it to pile up in the west, so much so that there is actually a 500-milimetre difference in sea surface height between Indonesia (west) and Ecuador (east)! This does a few things:

1. With the warm surface waters being piled up in the west, an 8°C temperature difference is created between the eastern and western equatorial Pacific, with the west being beautifully toasty. A warm ocean surface makes for a sexy, moist atmosphere and the result is a lot of rainfall. This is why Indonesia is beautifully lush.

2. On the other side of the Pacific, the wind pushing the surface waters away from the South American coast causes cold water from depth to rise to the surface (upwell), thereby leaving the ocean here chilly enough to embarrass you if you were dude wearing a speedo swimsuit. And, of course, the air overlying a cold ocean is typically dry and promotes little rainfall.

Ocean upwelling is a really important process, so it deserves a little conversation before we continue. When ocean creatures and critters die, their bodies sink, making the waters at depth wonderfully fertile. The upwelling of this water to the surface brings all this organic matter into the glorious sunshine and this leads to a surge in primary productivity. Of course, with great volumes of delicious algae, plankton and other tiny sea squishies available, every critter in the food chain is given the energy influx it needs to prosper, which essentially means lots of rodgering, lots of babies and lots of biological success. It also means lots of sushi for us.

Oh look! Krill!

Photo Source: http://www.krillfacts.org

So, we have a warm western equatorial Pacific with a rainy atmosphere and a cool eastern equatorial Pacific and a dry atmosphere. That’s the way it USUALLY is with the northeast and southeast trade winds happily blowing.

However: every two to seven years – and there doesn’t appear to be any strict rhyme or reason as to the frequency of this – the normally healthy trade winds stagger and weaken and you would scarcely BELIEVE the cluster f**k of consequences that follow.

 A Specific Account of the Cluster of F**ks That Follow

With the easterly trade winds fizzling out, all the beautifully warm water that is usually swept to the west is allowed to slough back into the east. This causes a tongue of warm water to spread out from the western coastline of North America (see diagrams below).

This diagram shows us December sea surface temperatures (SST) as they normally are over the Pacific Ocean (first image), as El Niño is setting in (middle image) and during the event’s crescendo (final image). You can really see the distribution of heat moving away from the west and becoming concentrated over the eastern equatorial Pacific.

 Image Source: El Niño Southern Oscillation, http://www.ic.ucsc.edu

If this picture series doesn’t tickle your fancy, the following video will…

Video Source: “Amazing New El Niño Animation Reveals Shocking New Details” Uploaded by ShantiUniverse on Youtube channel https://www.youtube.com/watch?v=pc2wYXK3qRk

A key point you must remember is that the ocean and atmosphere seldom, if ever, act independently of each other. One minor change in sea surface temperature can cause the atmosphere to overreact like your girlfriend approximately one week before Aunt Flo arrives for her monthly visit. A warm sea surface leads to greater evaporation, a more humid atmosphere and therefore more rainfall.

So, with ocean heat draining from the usually wet western Pacific, the region is typically left in drought while the east, which is usually dry, becomes unusually wet. On the ground, Indonesia and Australia can experiencing drought and, in Australia’s case, a much greater risk of catastrophic bush fire. On the eastern side of the Pacific, where the ocean has become anomalously warm, unusually heavy rainfall can lead to flooding with the risk being greatest to the southern states of America and Peru.

The El Niño event of 2010 was believed to drive the devastating floods that affected Peru.

 Image Source: http://news.sciencemag.org/climate/2014/08/ancient-piles-clams-reveal-peek-el-ni-os-past

The weakening of the trade winds also negatively affects the upwelling that usually occurs off the western coast of South America and by throttling the source of nutrients these marine ecosystems rely on, organisms of all echelons in the food chain take a major blow. Less importantly (in the grand scheme of things – don’t tell any local fisherman I’m saying this) our fishing industries also suffer. That’s right: less sushi.

Leave sushi alone!

If you thought that’s where it ends, think again. El Niño’s impacts spread further than a desperate housewife’s legs. The accumulation of vast reservoirs of heat energy at the eastern periphery of the equatorial Pacific drive significant changes in global atmospheric circulation, which essentially means that no matter where in the world you live, you can possibly expect the next few months’ of weather to be, uh… interesting.

Crappy Weather Coming To a Neighborhood Near You

Air in the atmosphere is constantly on the move and it’s thanks to our major global atmospheric circulations that all the crap going down in the Pacific is felt in varying degrees across the globe.  Here are some cherry-picked samples of other global consequences:

El Niño events are linked with wilder hurricane seasons in the Pacific. This is terrible news for the Philippines, which is already one of the most disaster-struck countries in the world. According to Colorado State University, there have been 21 Category 4 and above (read: holy crap that’s big!) hurricanes in the north Pacific this year alone. This total has obliterated the previous record of 17, which was set during the monster El Niño of 1997. The good news for Florida and southern Texas is that hurricanes in the Atlantic tend to stay home and pursue their hobbies during El Niño months.

Africa may be half the planet away, but the continent has a decent sized serving of interesting weather to expect. Southern Africa is currently in the throes of severe drought, while several East and North African nations are being pelted by heavy rainfall. I mean, can’t we ever just get the RIGHT amount of rain?? Why must it be one extreme or the other?

And, of course, we can’t leave out the main character in this story of wanton weather: MURICA! The following prediction maps for temperature and rainfall have been issued by the National Ocean and Atmospheric Administration (NOAA) on their amazing website, which you can view at www.climate.gov.

Temperature forecast for the period December 2015 to February 2016

 What we can tell from this map (aside from the fact that NOAA doesn’t give a hoot about Canada) is that there is a good chance of temperatures being hotter than usual in much of Alaska, Washington and the northern U.S. with dark red indicating a 70%+ probability of hotter than usual conditions. Texas and much of the southern states, on the other hand, may actually have to invest in a sweater or two. 

Class Dismissed: Your Take-Home Message
Is it the end of the world? Should you start looting your neighborhood grocery store and stocking up on bottled water and canned beans? No. Well, no to the first one: no harm ever came from having an extra can of baked beans, but you may want to prepare your home if you’re in an area that’s at risk of flood or drought. The question on the media’s lips is: is this particularly strong El Niño event proof of climate change and the severe weather we can come to expect from a globally warmer atmospheric environment?

Until we can say what causes the easterly trade winds to die down every two to seven years, we won’t be able to define the relationship between El Niño events and global warming. What is pretty evident – and has been talked about by climate scientists for years – is that a warmer atmosphere contains more moisture (due to greater evaporation) and more energy and is therefore more prone to the development of severe storms.

Your take-home message is this: The atmosphere is like the movie Cloud Atlas: It’s complicated and no matter how closely you study it, you still wonder what the f**k happened in the end. Just remember that the next time you hurl insults at the weatherman for getting the forecast wrong!

Northern Lights: The Sky's On Fire!

National Geographic filmmakers Claus and Anneliese Possberg put together this outstanding time lapse video showing the aurora borealis (northern lights) dancing and crackling across the evening sky in Norway.

Source: “Spectacular Norway Northern Lights” – National Geographic. Music by Justin Durban, http://www.justindurban.com. 

Youtube channel at http://www.youtube.com/watch?v=izYiDDt6d8s

For sexy servings of moist science in your box, I mean, in your inbox – LIKE the new Why? Because Science Facebook page! Just imagine replacing those vapid status updates and infuriating inspirational quotes with awesome videos of natural disasters, animals being interesting (and occasionally inappropriate) and riveting blogs on the coolest science topics!

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

 

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

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! 

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).

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.

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!

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.

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.

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?

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Somewhere Over the Rainbow, Photons Fly!

Image Source: “Rainbow Ignites” over Grand Canyon, uploaded by Cathy Smart to travel.nationalgeographic.com

Rainbows have enchanted humankind since our very beginnings, leading to the spinning of countless myths and legends about why and what they are. Just about every ancient civilization, culture and religion has its unique explanation of rainbows; all of them creative, but absolutely NONE of them correct. There is no pot of gold.

Aside from the fact that they look like a hippy has barfed across the sky, rainbows have quite a fascinating backstory involving the physics of light, which really isn’t all that complicated! In this blog, we’ll be taking a look at the physical laws and facts that give rise to some spectacular atmospheric masterpieces and a sky that would put a tie-dye T-shirt convention to shame.

The first ingredient on our palette is solar radiation…

You Need Sunshine, On a Cloudy Day!

Sunshine. It’s a simple concept: light from the sun. But one does not simply have interminable nuclear reactions without generating a spectrum of electromagnetic radiation. Our sun is a star and in keeping with the personality of stars, things are positively nuclear beneath its photosphere. These nuclear fusion reactions release a broad range of radiation types (see diagram below), from low energy, long wavelength infrared radiation (left) to the high energy, short wavelength Gamma radiation (right).

Image Source: The Electromagnetic Spectrum – faculty.olympic.edu

Slap bang in the middle of the electromagnetic spectrum is visible light, which only accounts for a narrow portion of the total energy generated by our sun day-after-day. This visible light pours out into space faster than Kris Jenner can say to Bruce “You’re becoming a what!?” covering the vast distance between the Sun and Earth in just 8 minutes and 20 seconds. It then smacks into our atmosphere and all its constituent gas and water vapor molecules. The photons (particles of light) that manage to escape atmospheric collision end their journey at the Earth’s surface, which is what brings warmth to our lives and color to our environment.

Snow White Light and the Seven Composite Colors

As I explained in the blog The Sky Is Only Sometimes Blue, visible (white) light is composed of seven different colors. Each of these colors has a different wavelength and ranges from the lower frequency, longer wavelength color red to the higher frequency, shorter wavelength color violet.

When visible light from the sun strikes a white surface, all of its seven dwarfs, I mean constituent colors get scattered in every direction, which is why we view the object as Snow White, I mean white. If that object is black, however, all of those seven colors become absorbed by the object, which is why you can cook an egg on the dashboard of your black Merc after leaving it in the sun for an hour.

Image Source: The Visible Light Spectrum – CultureLab/LabCulture at http://www.viralprojects.com

What about colorful objects?

Violet surfaces, like your gay best friend’s curtains, selectively scatter light with a wavelength of around 400 nanometers and absorb the rest. As such, you perceive the color violet (and bad taste) when you look at them.

Blue surfaces, like your lover’s eyes, selectively scatter light with a wavelength of around 450 nanometers. As such, you perceive the color blue and experience inappropriate clenchings in the nethers.

MIRRORS, interestingly enough, reflect all the seven colors of incoming visible light, but instead of scattering them in random directions, they reflect them at precisely the same angle as they arrived at and so the integrity of the image is preserved.

WHAT does this have to do with rainbows?

This discussion is intended to help you understand and appreciate the nature of visible light and the fact that it’s composed of different colors, which are capable of acting independently of each other due to their different wavelengths.

Now it’s when visible light strikes water droplets in our atmosphere that the real magic can begin to happen, potentially making it look like a unicorn wiped its butt on the horizon…

Prism (Not a Katy Perry Album)

Image Source: All The Pretty Colors – SeeMore Sights, http://www.seemoresights.net

So far, we’ve spoken about light as though it travels in a straight line, which is typically what it does between bouncing off of and being scattered by objects. However, this isn’t the case when it travels through water. When visible light travels from one medium to another – from air into the water – its pathway becomes slightly bent in a process termed “refraction.” This explains why objects under water look so strange: the light that enables us to perceive them is being refracted or bent and this makes your toes (or whatever body part you happen to be scrutinizing) look bigger and closer to you than they really are.

When sunlight passes through a water droplet, it deviates slightly from its incoming direction, because it’s refracted (see diagram below). A portion of this light is then reflected off the far surface of the raindrop. If this angle is at 40° – 42° to the original direction of incoming sunlight, we get a rainbow!

Image Source: What Causes a Rainbow? NASA/NOAA – scijinks.jpl.nasa.gov

So you see, rain droplets not only refract the sunlight that passes through them, they also act as prisms. The reason this process results in a rainbow is because the seven constituent colors of visible sunlight become refracted to different degrees: the shortest wavelength light (violet) becomes refracted the most and so it’s bent the most. The largest wavelength light (red) becomes refracted the least and so it’s bent the least. As such, when white light passes through a water droplet, it becomes split into its seven different personalities, from violet, blue and green to yellow, orange and red!

This is beautifully captured in the following 40-second video:

Video Source: “Light Split into Colors by a Prism” Uploaded by MadDogScience in YouTube channel http://www.youtube.com/watch?v=hLFcf58qD4w

A Rainbow Is Made!

We can now understand how white visible light, upon passing through water droplets suspended in the atmosphere, is split into its seven constituent colors. The final piece of the puzzle is looking at this process on the large scale. There are billions of water droplets in clouds or mist and each one disperses and refracts the sunlight that hits it. The overall result is a vast display of color in a circular or semicircular arc. Obviously, to us here on Earth, most rainbows would appear to be semi-circular, because the ground gets in the way of us seeing the other half. However, viewed from the air or from the following rare perspective at the top of Zambia’s Victoria Falls, we can see the full glorious monty:

Image Source: Circle Rainbow Over Victoria Falls, Zambia – Aug 2012 by Nicole Cambré/REX (2105841a): FULL WORDS LINK: http://www.rexfeatures.com/nanolink/ju4n

What I haven’t mentioned yet is that perspective plays a major role in our ability to visually enjoy rainbows. The sun has to be behind you and the angle of dispersion – the angle between the incoming sunlight and the direction the refracted light is exiting the raindrop – has to be between 40° and 42°.

Image Source: Rainbow Over Lake Ontario, uploaded by Melagoo on Weather Underground, http://www.wunderground.com.

Class Dismissed: Your Take-Home Message

Rainbows have this wonderful effect on people: they make us look. They compel us to forget for just a few seconds everything it is we are thinking/worrying/stressing about and look up to the sky and admire. Really, all a rainbow is is water droplets playing with the paths and emotions of sunlight… but they are beautiful and a reminder that God – or whatever deity is or isn’t up there – is in fact a fan of gay people.

Image Source: http://www.telegraph.co.uk

Copyright © Thea Beckman 2015

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

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.

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”.

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.

 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.

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.

Ermagherd! Ferkerng HUGE herlsterne!

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

On 23^rd 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

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.

Aurora Northern Lights: The Most Amazing Thing You'll Ever See

The aurora northern lights in Norway

No matter what your interests, hobbies, job, gender, race and age; no matter who you are and whether you’re interested in science or not… the most amazing thing you’ll ever see is the aurora. There are spectacles that come close: your baby’s first steps, sunrise on the gulf of Thailand, the first time you see a girl’s boobs up close (for free), or your dog dragging his arse across the living room carpet. But short of erupting volcanoes, oncoming tornadoes and meteor showers, the most amazing thing you’ll ever see is the aurora. And how could it not be?

The aurora looks very much like the gentle rippling of otherworldly greens, pinks, reds and even purples across the deep night sky: like some alien abstract artist swishing radioactive water paint across a black canvas. These colours stream and pulse, shimmer and crackle, swell and fade and ebb and flow. Watching the aurora lights must be the ultimate exercise in escapism. It must be impossible to imagine that you’re still on planet Earth with a view shown in the picture above and below. Not even Arthur C. Clark could paint – with words – a more vivid picture of a totally alien landscape.

The aurora lights glimmer and stream over a lagoon in Iceland

Is there anything more beautiful, more breath-taking and more enchanting? I wouldn’t know… I’ve never seen the aurora. But if the pictures and YouTube videos are anything to go by, I can’t even begin to imagine what it must be like to stand underneath a canopy of those shimmering ethereal lights. It would probably blow my fragile mind and break my tender heart.

So, What Are The Aurorae?

Contrary to the myths surrounding the aurora, this phenomenon is not your ancestors jiving across the sky, nor is it some kind of luminous bridge into the other world. Our ancient counterparts do, however, earn themselves an ‘A+’ for imagination and also for the foresight to invent the wheel. That has turned out to be kinda useful.

The Aurora is caused by the Sun rudely belching its charged gassy particles all over Earth’s outer atmosphere. This may sound horribly uncouth, but it is a most appropriate metaphor for the physical reality. Let’s take a closer look at the Sun… the long-winded explanation if you will.

Har har.

 Some Alka-Seltzer for the Sun, Please

Solar flares erupt from the Sun’s raging photosphere

The Sun is a star. And like all stars, its incredible mass causes unending catastrophic nuclear reactions in its hellish interior. Convection – great currents of outward bound surges of intense heat – transports mass to the surface of the Sun from its molten interior. As you can imagine, the surface of the Sun is anything but Swan Lake. It’s an intense bubbling conflagration of scalding heat.

Great bubbles of burning gas ride these convection currents like the turtles ride the East Australian Current in Finding Nemo and, in a prodigious release of energy, blast out of the Sun’s photosphere. This eruption of energy is known as a solar flare and it is a truly devastating phenomenon that can represent a staggering 17% of the Sun’s entire energy output per second… that’s approximately 600,000,000,000,000,000,000,000,000 joules of energy, give or take a joule.

The flares that erupt out of the Sun’s sexy corona (not beer) belch out obscene clouds of electrons and charged atoms, which stream out into space and collide with anything and everything in their path. Sometimes that anything and everything is our humble little planet.

Diagram: Solar flare activity and its effect on the Earth. The circular lines surrounding the sun-facing side of our planet represent our magnetic field and how it shields us from much of the incoming solar radiation.

Even though our tiny blue planet lies 15 billion kilometres (93 million miles) away, the streams of charged particles emitted by the Sun still reach us and they do so typically within a day or two of a solar flare occurring. This incomprehensible distance represents a leisurely stroll in the park for solar radiation, which doesn’t only consist of the light we perceive as daytime, but rather the entire electromagnetic spectrum, from high energy gamma rays (dangerous) right through to sluggishly slow and lazy radio waves (not dangerous).

These charged particles slap against the outer reaches of our atmosphere, which can damage the little microchips in satellites, disrupt power grids, interfere with radio signals and… *drumroll* cause the sky to incandesce with beautiful otherworldly lights!

A Charged Particle Walks into a Bar…

Charged particles from the Sun smack into the gas molecules that make up our atmosphere, exciting their electrons into higher energy orbits. Don’t worry, I won’t be testing you on this later. When these electrons have had a chance to chill out, they sink back into their normal orbits, releasing the excess energy they had in the form of light.

In plain English: A charged particle from the Sun walks into a bar and straight up to an oxygen atom. It smacks oxygen right in the gob, enraging oxygen which, as a result of its excited state, goes bright green with anger at the impudence of this charged solar particle. If the molecular victim in this analogy was nitrogen, it would have glowed red or blue.

On a vast scale of thousands of square kilometres, the effects of charged solar particles walking into zillions of bars and smacking zillions of oxygen molecules in the faces is staggeringly beautiful. And in spite of the violence of it all, the resultant visual spectacle looks like gentle waves of brilliant light caressing the night sky.

This mechanism may sound horribly confusing, but just because I used “charged” and “particle” in the same sentence doesn’t mean that comprehension is totally beyond you. In fact, we are surrounded by examples of the very same mechanism that cause the aurorae. Neon is a gas and when its atoms are excited, they too incandesce and emit a powerful glow. In the case of neon lights, the source of excitement is electricity.

Aurora Borealis, Aurora Australis

You may have heard of either, but they are essentially the same thing. Australis means “southern” in Latin – think Australia or Australopithecus, “southern man,” our earliest ancestor who was thusly dubbed because his (or her) crumbly ancient remains were discovered in southern African soil.

Borealis means “northern.” So if you live in or visit the icy clutches of the extreme north, in the countries bordering on the Arctic Ocean, you stand a chance of witnessing the Aurora Borealis, while those in the extreme southern latitudes, the Aurora Australis.

Class Dismissed: Your Take-Home Message

The biggest challenge I’ve faced in writing this has been to choose the correct words to convey the sheer otherworldly beauty of the aurorae. If I haven’t done this phenomenal phenomenon the full justice it deserves, then the following video of the aurora borealis definitely will. Isn’t it the most amazing thing you’ve ever seen? (No offence to the first pair of boobs you ever saw).

Video Source: “Spectacular Norway Northern Lights” uploaded by National Geographic on YouTube channel https://youtu.be/izYiDDt6d8s

The Sky Is Only Sometimes Blue

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?

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

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.

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!

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

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.

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?

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, 3^rd 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

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…

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?

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

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.

2. 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

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?