How it works Extreme weather

RECORD LARGEST HAILSTONE
BREAKERS
A hailstone measuring 20.5cm (8in) in diameter and
HAILSTONES
20.5cm weighing almost 1kg (2lb), even after melting a bit, fell on
the town of Vivian in South Dakota, USA in July 2010.

DID YOU KNOW? Approximately 24 people are injured by hail in the United States each year, but it rarely leads to fatalities

HUGE HAIL White ice layer Clear ice layer

The enormous balls of ice In much colder areas, In areas that are
that fall from the sky freezing occurs much just below 0°C
more quickly, trapping (32°F), freezing
Rather than just more air and producing occurs slowly,
being solid lumps of layers of white ice.
ice, hailstones actually consist allowing trapped
of several layers, much like an air to escape and
onion. This makes them forming clear ice.
incredibly tough and allows
them to grow to large sizes, Rotating ball © Corbis; Rex Features; Dreamstime; Thinkstock
creating hail that is extremely
destructive. Hail is often The ice builds up on the
confused with ice pellets, frozen downward-facing side of the
raindrops that consist of one hailstone, but it rotates as it
layer and are much weaker. falls to form a sphere.

Rolling hailstones

How layers of ice build up
within a storm cloud

Droplets freeze Hail grows

When the droplets reach As the ice nucleus falls through
very high altitudes, the areas of varying temperatures,
colder temperatures freeze
them into an ice nucleus. it builds up new layers of ice.

Melted hail Growing bigger

If the hailstones are Strong updrafts lift the hail back
any smaller, they melt up so that it can fall again,
before leaving the
cloud and fall as rain. allowing more layers to build up.

Hail falls Warm
updraft
Eventually the hailstones
become too heavy for the Moisture in the air
updraft and fall from the is lifted up into the
cloud to the ground below.
storm cloud by a
warm updraft,

where it cools into
water droplets.

101

SCIENCE OF WEATHER

Weirdest weather

Dirty thunderstorm

It is the combination of ice
and ash that has lead volcanic
lightning to become known as
a dirty thunderstorm.

Second phase

It is thought that the
later sparks are caused
by ice particles higher up
in the ash cloud colliding.

Tall plumes

Lightning is considerably more
frequent in volcanic plumes
greater than 7,010m
(23,000ft) in height, because
temperatures are colder at
higher altitudes.

VOLCANIC Normal lightning
LIGHTNING
Normal lightning is
The big eruptions that really caused by ice particles in
light up the sky storm clouds colliding
and separating to create
A volcanic eruption is an electric charge.
spectacular and violent
enough as it is, but sometimes it is
accompanied by big flashes of
lightning too. However, this
lightning doesn’t descend from
storm clouds in the sky. It is
generated within the ash cloud
spewing from the volcano, in a
process called charge separation.

102

RECORD MOST LIGHTNING STRIKESVenezuela’s Catatumbo Lightning occurs almost every other
BREAKERS
night over the mouth of the Catatumbo River. On average,
STRIKING STATS
250 per km² there are 250 lightning bolts per square kilometre per year.

DID YOU KNOW? It’s thought volcanic lightning of the Minoan eruption in 1500 BCE inspired Zeus’s thunderbolts in Greek myths

What is charge
separation?

1The particles within the cloud start
out neutral, with an equal number of
electrons and protons, meaning that
they have neither a positive or negative
charge to them.

New discoveries

Volcanic lightning was a
relatively understudied area of
science until 2000, and its
cause is still merely speculated.

Ice crystals form 2As particles heat up, they collide
and transfer electrons in a process
As temperatures are cooler at known as charge separation. This
higher altitudes, the vapour causes some to become positively
cools and eventually turns into charged, and others negatively charged.
ice crystals, which collide to
create lightning. Difficult to study 3A difference in the aerodynamics of © Rex/Sipa Press; Rex/Ricardo A. Mohr Rioseco
the positive and negative particles
Initial sparks Volcanic lightning causes them to separate, so some parts
typically occurs during of the cloud become more positive, and
The first sparks of the beginning stages of others become more negative.
lightning during an an eruption, making it
eruption are believed very difficult to record 4 The electrons flow back towards
to be caused by ash and study. the positively charged particles
particles colliding as when the charge separation gets too
they are ejected. Water-laden great. This forms sparks of electricity
magma and neutralises the particles again.

These ice particles 103
form when water
dissolved in the
magma becomes
vapour and rises
out of the volcano
during an eruption.

SCIENCE OF WEATHER

Weirdest weather

ROLL
CLOUDS

The odd-shaped clouds
that roll across the sky

Although they
look like
horizontal tornadoes, roll
clouds are actually
completely harmless. Along
with shelf clouds, which are
more wedge-shaped, they
are a type of low horizontal
cloud formation, known as
an arcus cloud. The
difference is that shelf
clouds are only created by
thunderstorms and remain
attached to the main storm
cloud, while roll clouds can
be formed by a number of
different weather systems
and are often independent
from any other clouds.
They are the result of a
mass of cold air meeting a
mass of warm air, so can be
formed by thunderstorms,
cold fronts or sea breezes.

EL NIÑO Normal year RAINING ANIMALS

The cyclical weather change Trade winds The very real threat of amphibious rain
that causes unusually high Warm water Although there are no accounts of it actually raining
ocean temperatures cats and dogs, other animals, such and fish and
Cold water
Every few years, the El Niño year frogs, have been seen to fall from the sky in some parts of the
trade winds that world. This occurs when waterspouts – small tornadoes that
blow towards the west across form over water – suck up low-weight items, such as small
the Pacific dwindle, causing a creatures, with their low-pressure core. When these
pool of warm water to form waterspouts hit land, they lose some of their energy and slow
along the equator. As this down, releasing whatever it is that they are carrying. Their
warm water travels eastward, spinning winds can reach up to 480 km/h (300mph), helping
it triggers severe weather, such them to suck up objects from up to 1m (3ft) below the surface.
as increased rainfall and
flooding in North and South Trade winds weaken
America, and extreme drought or even reverse
in the West Pacific. South
American fishermen named Warm water
the phenomenon El Niño,
Spanish for “The Christ Child,” Cold water
because it usually arrives
around Christmas time.

104

STRANGE Which of these Answer:
BUT TRUE has fallen as rain?
While frogs and other sea creatures are the most
HARD RAIN A Tomatoes B Coal C Meat common form of unusual rain, sightings of tomato,
coal and even meat falling from the sky have also
been recorded. It’s likely that they were picked up
and dropped by strong winds and tornadoes.

DID YOU KNOW? Hail can occur in any thunderstorm, but large hail is most common in rotating supercell thunderstorms

Updraft Wind speed Clouds
rolling in
As hot air rises Differences in
from the surface wind speed How roll clouds form
of the Earth, it above and below from a thunderstorm
condenses and the cloud cause
cools to form it to roll parallel
storm clouds. to the horizon.

Cloud forms

Due to its higher density,
the cool air lifts the warm
air above it so it condenses

and forms cloud.

Downdraft Gust front

Rain falling from a storm cloud The leading edge of the
creates a downdraft of cold air downdraft, known as a
that spreads outward across gust front, cuts under
the Earth’s surface. the warm air being
drawn into the updraft.

ST ELMO’S FIRE FIRE RAINBOWS Roll clouds can stretch for © Thinkstock; North Wind Picture Archives / Alamy; Martinao / Nikmerkulov / Dreamstime ; Rex Features
hundreds of miles and keep
The flames and sparks that climb The very rare colourful clouds
ship masts and church steeples created by ice crystals and the Sun rolling for several hours

Named after St Erasmus, the patron saint of Officially known as Fire rainbows are so
sailors, St Elmo’s Fire is the glow of blue flames circumhorizontal arcs, called because the wispy
often observed at the top of tall structures, such as these rare clouds only occur in very
ship masts, in a thunderstorm. It occurs due to specific conditions. Firstly, you must clouds look like bright
charge separation, just like lightning. However, it be within 55° north or south of the flames licking the sky
involves a difference in charge between the air and equator in the summer months.
an object, rather than the air and the ground. It is Then there must also be cirrus 105
most common on pointed objects as they discharge clouds, which are thin and wispy and
electrical energy at a lower voltage level. exist at high altitudes where the
temperature is very low. Due to their
location, these clouds are formed of
plate-shaped ice crystals, and when
the sun rises to higher than 58°, its
rays refract through the crystals,
which act like prisms and split into
individual colours to create a rainbow.

SCIENCE OF WEATHER

Weirdest weather

FIRENADOES Firenadoes are
usually small, but
The deadly tornadoes with added fire some have grown to
Firenadoes are actually more be 122m (400ft) tall
closely related to whirlwinds and 15m (50ft) wide

and dust devils than tornadoes, which is
why they are also known as fire whirls and
fire devils. They usually grow from wildfires,
but have been spotted at the scene of house
fires too, and can vary greatly in size.

Great whirls of fire Short life span Flames drawn in

What fuels a dangerous As the hot air rises, it cools and As it rotates, the
spinning vortex of flame? weakens the vortex, which is whirlwind draws in
why firenadoes typically last flames from the fire
only a few minutes.
upwards into its
Spreading flames spinning vortex.

Firenadoes can move Column
quickly and eject flaming rotates
debris, helping to spread
the fire further. As it rises, the
column of air
Independent firenado begins to whirl
around a vertical
The now-vertical vortex splits axis, much like
off and intensifies by sucking water draining
in more air and flames. from a basin.

Lifted upright

When the horizontal roll
encounters an updraft of
warm air it lifts it upright.

Air rolls

The difference in speed
of both the hot and
cold air causes it to
roll horizontally.

Horizontal Hot air rises
firenadoes
Fire heats up the air above the
Fire tornadoes can also ground and causes a column
form horizontally, when hot of warm air to rise upwards.
air behind the fire meets cold
air in front of it.

106

5TOP Haboobs Amazon lifeline The Dust Bowl Blood rain Harmful dust
FACTS
1 Dust storms are named after 220 million tons of dust is 3 Severe drought in the USA’s Great 4Clouds can transport dirt from 5 The dust in dust storms can
DUST STORMS the winds that generate them. transported from the Sahara to Plains in the 1930s caused a period dust storms for thousands of sometimes carry pollutants
So a haboob is generated by the Amazon rainforest each of dust storms called the Dust Bowl. miles. It eventually falls as and toxins, such as salt,
the strong wind that occurs year, supplying it with essential Agriculture was severely affected rain, which leaves a reddish sulphur and pesticides, that
primarily along the southern minerals and nutrients to keep and hundreds of thousands of dust when it dries, leading it can damage crops and be
edges of the Sahara in Sudan. the soil fertile. people were displaced. to be labelled ‘blood rain’. harmful to living things.

DID YOU KNOW? Specific sprites are classified by shape. Carrot, broccoli and jellyfish sprites have all been identified

DUST Dust storms
STORMS originate in arid or
semi-arid regions
The blizzards of dirt where the soil is dry
that black out the sky and loosely held on

Dust storms are started the surface
by gust fronts, the
downdrafts of cold air from
thunderstorms that hit the ground
and spread outward. As the wind
passes over the ground, it moves the
dust particles and starts a process
called saltation. When the particles
bounce along to the surface, they
start a chain reaction, hitting other
particles and causing them to
bounce too. As these particles hit
each other and the ground, they
acquire a negative charge that repels
them from the positively charged
surface. This lifts them higher,
where they get picked up by the
wind and blown further.

Elusive light show Electromagnetic pulse Colourful halo SPRITES,
ELVES AND
What causes transient Elves are caused by the abrupt, As this energy passes upward BLUE JETS
luminous events? rapid acceleration of electrons, through the base of the
known as an electromagnetic The flashes of light that occur
Red glow pulse (EMP), in a lightning strike. ionosphere and spreads outward, high above storm clouds
it causes gases to glow red.
Sprites get their red colour As well as the regular lightning © Science Photo Library; Corbis; Cholder / Dreamstime
because electrons collide with Upwards that we experience in the
nitrogen molecules to create a lightning troposphere, the lowest layer of the
colourful glow. Earth’s atmosphere, thunderstorms
Blue jets occur when can also generate further activity
Sparks form a large positive much higher up. Transient luminous
events (TLEs) are colourful flashes of
When the charge separation charge at the top of light that occur in the middle and
between the cloud and upper a storm cloud upper atmosphere and take the form
atmosphere becomes too great, of sprites, elves or jets. As they are
electrons flow to create a spark. triggers an upward very rare and last for just a fraction of a
lightning strike. second, these phenomena are usually
Sprite impossible to see with the naked eye
beginnings Tall storm and very difficult to capture on
clouds camera and study. Very little is known
When a positively about them, but high-sensitivity
charged lightning The higher the cameras and observations from space
bolt strikes the storm cloud, the are helping scientists to learn more.
ground, it leaves more likely a blue
the top of the jet is to appear, but 107
storm cloud
negatively charged. they are not
directly associated

with cloud-to-
ground lightning.

SCIENCE OF WEATHER The colours in secondary
rainbows are reversed,
Weirdest weather
with blue on the top and
MULTIPLE red on the bottom
RAINBOWS

The awe-inspiring double, tertiary
and quaternary rainbows

Rainbows form when
sunlight bounces off of the
inside of water droplets suspended in
the air. To create one rainbow, the light
must bounce once inside the droplet.
However, if the light bounces multiple
times, more rainbows form. It is
thought that larger water droplets that
have been flattened by the
surrounding air are needed to form
double rainbows. These so-called
‘burgeroid’ droplets have a larger
surface area for reflecting light more
than once. If the light bounces three or
four times, tertiary or quaternary
rainbows form, but they are usually
too faint for the naked eye to see.

Inside a double Double refraction Refraction
rainbow
In secondary rainbows, In primary rainbows,
How multiple refractions sunlight bounces off of sunlight enters a water
create multiple rainbows the inside of water droplet and bounces off its
droplets twice, reversing inner surface in a process
the order of the colours.
known as refraction.
Fainter effect Angle of
refraction Wavelengths separate
Secondary rainbows
appear fainter because Red light refracts at As each colour of light has a
only some of the light an angle of 42°, different wavelength, it is
reflected a second time whereas blue light exits refracted at a slightly
reaches your eyes. at 40° from where the different angle.
sunlight entered.
Greater angles Alexander’s Band
Colours scatter
The red light refracts at 52° and the The area between the
blue at 54°, so a secondary rainbow By refracting at different two rainbows is known
appears 9° above a primary rainbow. angles, the different
wavelengths of light as Alexander’s Band,
Rainbow scatter so that we see named after Alexander
effect the individual colours.
of Aphrodisias who
Only one colour first noticed it.
from each
droplet will Darker
refract at the in-between
exact angle
necessary to Alexander’s Band
directly reach appears to be extra
your eye.
dark because the
108 droplets within it
are refracting light
at angles that don’t
reach your eyes.

DID YOU KNOW? The noise levels of some singing sand dunes have reached 110 decibels, which is as loud as a motorbike

SINGING Ball lightning only lasts for a few
SAND seconds, as it disappears once
DUNES
the silicon oxide has burned out
The mountains of sand that
can hit the low notes BALL LIGHTNING

In several of the Mysterious orbs of light that float across the sky
world’s driest When lightning strikes the ground, it
climates, sand dunes vaporises silicon oxide in the dirt. If the soil
regularly emit a strange
low-pitched rumbling noise also contains carbon, perhaps from dead leaves, it
that can be heard from up to will steal oxygen from the silicon oxide, turning it
ten kilometres (six miles) into pure silicon vapour. As the silicon
away. These singing or recombines with oxygen in the air, the reaction
booming sand dunes baffled creates an orb of light.
scientists for decades, but it
is now believed that the
sound comes from sand
vibrating within the top
layer of the dune. This
produces a single musical
note, typically G, E or F. The
thicker the top layer of sand,
the lower the note it creates.

Singing in Steep slope 30° These so called ‘hole-punch
the sand clouds’ are the result of
The dune must be over 36.5m extremely localised snowfall
How dunes create (120ft) tall with a slope of over
their own tunes 30 degrees in order to create FALLSTREAK
a big enough avalanche. HOLE

Audible sounds Good vibrations The phenomenon that
punches a hole in the clouds
The waves on the surface As the grains of sand
act like a speaker, converting move, they collide Cirrocumulus and altocumulus clouds
these vibrations into sound are composed of ‘supercooled’ water
waves and amplifying them. and rub together to droplets that are below freezing temperature, but
create vibrations. can’t freeze because they don’t have any particles
Hot and dry around which ice crystals can form. When an
Sand avalanche Waves of sand aeroplane passes through the cloud, it triggers an © Thinkstock; Thierry GRUN / Alamy
In order to sing, expansion of air that causes the surrounding
the sand must When wind or human These waves of temperature to drop below -40°C (-40°F). This is
be extremely dry intervention destabilises vibration are trapped cold enough to freeze the droplets, which fall as
so that it can the crest of the dune, it within the dry surface snow and leave behind a hole in the cloud.
move freely collapses and triggers layer of the dune, above
down the dune. an avalanche of sand. the wet sand below. 109

SCIENCE OF WEATHER

How the seasons work

How the seasons work

Get out your flashlight and 3. Summer solstice
a beach ball, it’s time to
talk about tilt On roughly 21 June, the North Pole tilts the closest to
the Sun, bathing the northern hemisphere in
The Earth is a wonky planet. Every year we make summer and the southern hemisphere in winter.
a complete near-circular revolution around the
Sun, but every day our planet spins around a lopsided 2. Tilted axis
axis. This imaginary line that runs through the centre of the
planet from the North Pole to the South Pole is tilted at a 23.5º The seasons are powered by the angle
angle, and this wonky tilt is the reason for the seasons. of the Earth’s axis, which tilts 23.5
During June and July in the northern hemisphere, the degrees away from being perfectly
North Pole is tilted toward the Sun and South Pole tilted away. perpendicular with its orbital plane.
This means that solar radiation hits the northern hemisphere
“head on” and is absorbed in a more concentrated area. 1. Revolution
Because the southern hemisphere is angled away from the Sun,
the same amount of solar radiation is spread across a much The Earth travels in an elliptical orbit
larger surface area. around the Sun, but the path is nearly
But differences in solar intensity aren’t enough to create circular, meaning our distance from the
summer and winter. The tilt of the axis also creates radical Sun is relatively constant year-round.
differences in the length of solar exposure, what we define
as daylight. If we go back to our June and July example,
the northern hemisphere is directly facing the Sun, which
means the Sun carves a high path across the sky, creating
longer daylight hours. In the southern hemisphere, the Sun
travels much closer to the horizon, which limits daylight
hours significantly.
The combination of longer days and concentrated sunlight
gives us summer. Shorter days and dispersed solar energy
gives us winter. Autumn and spring mark the transitional
periods when days are getting longer or shorter and
temperature variations tend to be less extreme.

January in Australia is hot
enough to cause bush fires

1. The tropics

All year long, the region within the tropics
of Cancer and Capricorn receives the most
direct and intense sunlight.

2. Concentrated surface area

Since the Sun’s rays strike the region around the equator
at nearly a 90˚ angle, the intensity of the radiation is
concentrated on a relatively small surface area.

3. Scattered surface area

Near the poles, the Sun’s angle of incidence is much
lower, meaning solar radiation scatters across a much
larger surface area, losing its intensity.

110

5 TOP Long summer “Tropical” Venus Serious tilt Springtime on Uranus Long days
FACTS
1 Because Neptune is so far away 2 Since Venus’ axis only tilts at a 3 Uranus spins on an axis tilted 4 There are no April showers on 5 Due to its slow rotation on its
SEASONS ON from the Sun, it takes over 164 3˚ angle, all of its seasons are at 98˚, and much of the planet Uranus. When spring arrives axis and rapid movement
OTHER PLANETS Earth years to complete a roughly the same, which is bathed in continuous after 20 years of darkness, the around the Sun, a day on
revolution. That makes its results in a rather steamy darkness or continuous light warming atmosphere Mercury is the equivalent of
summer around 40 years long. 750K all year round. for 20 years at a time. generates violent storms. 176 Earth days.

DID YOU KNOW? Contrary to common sense, the Earth is closest to the Sun (147,300,000km) on or around 3 January

5. Vernal equinox 4. Winter solstice Solstice vs
equinox
At this point in the orbit, the Sun shines evenly across the At the opposite end of the Earth’s orbit, it’s
entire face of the Earth, neutralising the effect of the tilted axis. the southern hemisphere’s turn to receive The winter solstice is commonly
the most direct sunlight while Europe and referred to as the “shortest day of
the United States enter winter. the year”. Although 21 December is
still 24 hours long, it has the fewest
The hours of sunlight. On this day, the
cycle of North Pole is tilted the furthest
seasons from the Sun, causing the Sun to
trace a low path in the sky. As the
The seasons correspond not only months pass, the Sun’s course
to the Earth’s position in orbit drifts upward until we reach the
around the Sun, but your physical vernal equinox, a day with exactly
location on the Earth. At different 12 hours of light and 12 hours of
times of the year, different parts of darkness. Around 21 June, the
the planet receive more direct North Pole tilts closest to the Sun,
sunlight and longer days (spring the Sun rides high in the sky and
and summer), while others we have the summer solstice,
receive less direct the longest day of the year. As
sunlight and shorter the Sun’s path sinks back toward
days (fall and winter). the horizon, we reach the
autumnal equinox, the second
time all year when day and night
are perfectly equal.

Here comes the
Sun… flower

The Sun’s intensity varies depending Seasons at
on where you are on the planet the top of
the world
6. Autumnal
equinox For people living at the equator,
seasons are virtually meaningless.
As with the vernal The closer you are to the equator,
equinox, the first day of the less your weather is affected by
autumn has exactly 12 the tilt of the Earth. If you tilt a
hours of daylight and 12 globe back and forth, the top and
hours of darkness. bottom appear to move further
away from you, while the middle
Solar intensity will remain relatively central.

It gets hotter as you move closer to the with something called the ‘angle of solar exposure of Iceland, which sits In high-latitude regions the Background image courtesy of NASA
equator because the region between incidence’. During the vernal and right on the Arctic circle at roughly 66º differences between seasons are
the tropic of Cancer and the tropic of autumnal equinoxes, the Sun’s rays north of the equator. During the extreme. In the dead of winter in
Capricorn receives more direct and strike the equator at a precise 90º autumnal equinox, the Sun’s rays hit northern Norway, the northern
concentrated solar radiation. angle. Since the solar radiation rains Iceland on a much shallower angle of hemisphere is tilted so far away
down on the Earth so directly, its 70º, spreading their radiation across a from the Sun that it doesn’t peak
The reason for this is not because intensity is concentrated in a relatively much larger surface area, thereby over the horizon for two months.
the tropics are ‘closer’ to the Sun than small area. Compare this with the decreasing their intensity. In the middle of summer, the Sun
other parts of the planet. It has to do travels directly overhead, tracing a
loop through the sky that holds
back the night for 2.5 months.

111

SCIENCE OF WEATHER

Arctic ocean

How the Arctic
Ocean freezes

It’s difficult to imagine such a huge expanse of
water freezing solid, so how is it possible?

Arctic sea ice is that which forms on develop minuscule ice crystals; this slushy water
the Arctic Ocean during the winter is called frazil ice. A further drop in temperature
months. Pure water, which contains no causes the frazil ice to thicken. Pockets of salty
other molecules, substances or impurities, slush accumulate until they become so heavy
freezes at 0 degrees Celsius (32 degrees they start to sink. This leaves the top layer of icy
Fahrenheit). The world’s seawater, on the other crystals with significantly less salt content. The
hand, contains around 3.5 per cent dissolved freezing point of this surface water therefore
minerals and salts. This additional material becomes higher and the falling temperatures
lowers the freezing point of the seawater to enable the crystals to solidify into pack ice.
around -2 degrees Celsius (28.4 degrees
Fahrenheit) because the freezing point depends This pack ice grows to become one huge
on the number of molecules present in a solution, floating sheet (made up of many smaller floes),
as well as the type of molecule(s). the thickness and coverage of which varies over
During the winter months, when the air the year, but reaches its peak in March. During
temperature in the Arctic starts to fall the warmer summer months, meanwhile, the ice
dramatically, a deep layer of seawater begins to begins to retreat and break up, reaching its
lowest extent around September.

112

THE AREA BY WHICH ARCTIC SEA
STATS
10% 8 >30ICE IS RECEDING PER DECADE
ARCTIC TRIVIA SEAS AROUND NUMBER OF
THE ARCTIC OCEAN NATIVE PEOPLES

~4 million 50cm -68°CPOPULATION
ANNUAL COLDEST TEMP
PRECIPITATION ON RECORD

DID YOU KNOW? At its current rate of decline, it’s predicted there will be no Arctic sea ice left by the end of the century

A satellite shot of sea ice floes and How polar ice
icebergs off the coast of Antarctica affects the
world climate

Sea ice at the poles is important because it
influences the weather across the entire
planet. The ice acts like a mirror,
deflecting the Sun’s rays back into the
atmosphere. As the ice melts, more of the
‘dark’ ocean beneath, capable of
absorbing the Sun’s heat, is exposed.
When the Arctic is frozen, warmer water
entering from the Pacific or Atlantic
begins to cool, becoming dense and
sinking. This displacement of water
drives the circulation of Earth’s oceans,
affecting weather and conditions
throughout the world. So, in many
respects, the amount and extent of Arctic
sea ice is critical to the global climate.

High reflection

The white sea ice cover acts like a mirror,
reflecting the Sun’s rays back out to space,
preventing the sea from heating excessively.

Sea exposed

As the ice melts, there is more dark seawater to
absorb sunlight, which further melts the ice.

Low reflection

The more sunlight absorbed by the seawater, the
more the ice melts until, eventually, significantly
less light is reflected back into space.

113
© SPL
4x © NASA

SCIENCE OF WEATHER

The carbon cycle

The carbon cycle

You’re breathing it out right now, but
where’s it been before and where’s it off to?

ATMOSPHERE

PLANT GROWTH Pedosphere EXCHANGE
AND DECAY SOIL TO
Carbon is also released from microbes
in the soil at a very slow rate and into ATMOSPHERE

the atmosphere.

LAND USE
CHANGES

FOSSIL FUEL
EMISSIONS

FIRES

Biosphere TERRESTRIAL
VEGETATION

Plants absorb carbon for photosynthesis, SOIL AND ORGANIC MATTER FOSSIL FUEL AND CEMENT
this carbon is passed onto animals that PRODUCTION
eat those plants and is transferred Burning
through the food chain. Carbon is COAL DEPOSIT
released back into the atmosphere Organic matter is burnt and a OIL AND GAS DEPOSIT
through animal respiration and released small amount of carbon contained
into the soil through plant and animal
decay. The exchanges are fast, occurring within is rapidly transferred into
in less than a year with most carbon the atmosphere.
absorbed by plants and some put back
into the atmosphere.

COAL DEPOSITS

Geosphere

This is the area below the Earth’s surface,
where carbon is found in the solid form of coal
or the liquid form of oil. These are millions of
years’ worth of dead matter, compacted and
preserved to form these fuels which are burnt to

provide power.

114

5 TOP Dry ice Fizzy drinks Carbon dating Teeth whitening Fire extinguishers
FACTS
1 Dry ice is solid carbon dioxide. 2 When held under pressure 3 The age of fossils and minerals 4 Carbon is a key element 5 A fire extinguisher containing
USES OF It is frozen carbon dioxide with carbon dioxide dissolves in can be found by using involved in teeth whitening carbon dioxide is mainly used
CARBON a temperature of -78.5°C and water, and it then causes carbon-14 which is a treatments, found as for fighting electrical fires.
melts into a gaseous rather bubbles on your tongue as it radioactive isotope of carbon. carbon amide peroxide in The carbon goes back into the
than liquid form to create the forms a carbonic acid as you It has been used to date the both dentist and over-the- atmosphere without leaving
popular smoke effect. take a gulp. age of dinosaur bones. counter treatments. any harmful fumes.

DID YOU KNOW? The carbon within you now will probably have been used in the ocean and helped a plant photosynthesise

Carbon is a greenhouse Carbon moves from the atmosphere into the atmosphere through therefore releasing the carbon back
gas that helps trap heat and into plants. In the atmosphere it is respiration when they breathe out CO2. into the atmosphere. Some carbon also
keep the Earth warm. Just combined with oxygen and found as enters the sea as the ocean absorbs it
as water is transferred around the carbon dioxide. Plant photosynthesis When plants and animals die the from the atmosphere.
Earth, carbon atoms also follow a draws the carbon out of the air to make carbon is transferred into the soil when
cycle and are used again and again. plant food. The carbon then moves decomposition occurs. Some of this Although the carbon cycle is a
You might not be able to see carbon but from plants into animals as animals carbon will end up buried miles natural process it can be affected by
it is a vital part of how our world works eat the plants. The carbon moves up the underground and so will eventually human activity; our burning of fossil
and it moves around the Earth in a food chain as each animal is eaten by make fossil fuels. These fossil fuels are fuels means there is 30 per cent more
variety of ways. another. Animals release carbon back then burned and used for power, in the carbon dioxide in the air now than
form of factories, cars and so on, 150 years ago.

Exchange rates VERY FAST (< 1 year) FAST (1 to 10 years) SLOW (10 to 100 years) VERY SLOW (> 100 years)

Fossil fuels “Some carbon
also enters the
Fossil fuels found deep underground sea as the ocean
emit carbon, in the form of carbon absorbs it from
dioxide, into the atmosphere when the atmosphere”
used. This includes factory work,
cement production and use of
vehicles. It is a speedy
transmission but is a process
that is ever increasing and
putting more and more carbon
into the atmosphere.

EXCHANGE OCEANS TO
ATMOSPHERE

Hydrosphere Deep sea

Carbon moves between the ocean and the atmosphere Some carbon is transferred into the
through diffusion. Carbon is used by organisms in the deeper ocean where it can stay for 1,000
ocean food web and re-released. Generally carbon is years. Phytoplankton uses carbon to make
released into the atmosphere by tropical oceans and
absorbed by high-latitude oceans. It is a fast process shells; when they die they fall to the
occurring between one and ten years with a fairly even bottom of the ocean where they are
buried and compressed to become
transferral of carbon being released and absorbed. limestone, which in time can be used as

fossil fuel.

SURFACE WATER

DISSOLVED EXCHANGE
ORGANIC SURFACE WATER
CARBON TO DEEP WATER

GAS HYDRATES MARINE ORGANISMS INTERMEDIATE AND
SURFACE SEDIMENT DEEP WATER
MARINE SEDIMENTS AND
SEDIMENTARY ROCKS

115

SCIENCE OF WEATHER

Wind erosion

How wind erosion works
Learn about how the sheer power of the wind
can shape and sculpt whole landscapes Other types of
desert erosion
Ever wondered how desert stacks get to them into the streamlined shapes that follow the
where they are, how huge archways wind’s path – a process known as abrasion. Over Although the deserts are known for having very
appear out of the rock and how colourful time, this gradual erosion produces the incredible little rainfall, the landscape can also be shaped
stripes stretch along rocky ledges in the desert? All landforms we associate with the desert, which are heavily by water action. Rare flash floods are
of these are formed by wind erosion – the fancy term known as ‘yardangs’. caused by thunderstorms and cloudbursts. The
for which is Aeolian processes. resulting rainwater picks up debris from the
In the wide-open expanses of deserts, the sheer The type of rock in an area greatly affects how the desert floor and charges its way through the
force of the wind can eat into softer types of rock, wind shapes it. Softer rock is easily eroded, while landscape. The force and action of the water can
such as sandstone. Particles of rock are removed and harder rock is far more resistant and is likely to be carve its way through rock, and this is helped by
lifted up by the wind (this is known as deflation) and polished by the ferocity of the wind, resulting in the water’s sediment load that, similar to the
then, as the wind blusters its way through the arid smooth, buffed formations. Softer rock is carved out wind, eats away at the rock in its path. The steep
landscape, its path governed by the rock formations by the wind, producing much more pronounced slopes and lack of vegetation in the desert
that dominate the terrain, these particles act almost effects, while a mixture of both hard and soft rock environment means there is little in the way to
like sandpaper on the rocks and gradually transform types can produce incredible formations such as stop these flash floods tearing through the
buttes and arches. landscape and making their mark on the desert
terrain, carving out canyons and gullies and
buffering rocks as they go.

Monument Valley in Utah, USA is a Water flowing through a desert landscape can
famous example of extreme wind erosion shape the environment as much as wind erosion

How rock archways are formed

Over time, erosion by the wind helps to hollow out these incredible natural structures

Cracking Overlying rock Rain and ice Archways widen Collapse

Geological processes can The wind gradually Rainwater dissolves some Wind erosion continues Eventually, the arch is
cause the rock to crack, erodes the layers of rock of the soft rock’s chemical to wear away at every eroded so much that it
creating fissures and above the cracks. makeup, while water in surface of the exposed collapses, leaving two
exposing the softer small cracks freezes and archway, constantly rock pillars standing
layers of rock weakens the rock. widening it. either side.
within.

Rock layers Cracks deepen Rockfalls

Different types of As the wind rushes The weakened softer rock begins
rock with different through the cracks to crumble and eventually falls
properties form and they are gradually away, leaving an arch of more
shape the eroded away and begin resistant rock.
landscape in layers. to widen and deepen.

116

DID YOU KNOW? The biggest cloud is the cumulonimbus. They’re dark and can contain millions of tons of water

Atmospheric Atmosphere layer by layer
temperature
Take a trip through Earth’s atmosphere to see
Why does the air temperature the location of the hottest and coldest areas
radically fluctuate with altitude?
1. Troposphere Temperature (°F)
We’re taught hot air rises and we can see this in
practice when a hot-air balloon climbs into the This extends up to about 12km –140-120-100-80 -60 -40 -20 0 20 40 60 80 100 120 140 160 180
sky. So why does the air temperature plummet (7mi) and is where our –75
at greater altitudes? There are a number of variables that weather occurs. Temperature 120–
affect atmospheric temperature and the best known is drops about 6.5°C per
solar radiation. This doesn’t heat the air directly though. kilometre here. 110– –70
Lapse rate describes the general decrease in atmospheric 100– 4. Thermosphere –65
temperature with height, which occurs because the 2. Stratosphere 90–
atmosphere is heated by conduction with the Earth’s –60
surface. The farther you move from the surface, the less The bulk of the ozone layer is –55
dense the air is and the more it struggles to retain heat. here and the temperature
But the temperature doesn’t follow a unidirectional increases to just below 80– –50
gradient. For example, while at 80 kilometres (50 miles) it freezing near the
can be -100 degrees Celsius (-148 degrees Fahrenheit), the stratopause. Altitude (km)
air is much warmer at 115 kilometres (70 miles) due to Altitude (mi)
ionising radiation. 3. Mesosphere 70– –45
3. Mesosphere –40
Between 50km (31mi) and 60–
100km (62mi) temperatures –35
plummet because of CO
50– –30
2
40– –25
cooling and low solar
heating. 30– 2. Stratosphere –20
–15
4. Thermosphere
20–
Stretching up to 600km –10
(373mi) from the Earth’s
surface air here can reach 10– 1. Troposphere –5
1,800°C (3,272°F)
but is too thin for us to feel it. 0– 0

–100-90-80 -70 -60 -50-40 -30 -20 -10 0 10 20 30 40 50 60 70 80

Temperature (°C)

The different levels of the
Earth’s atmosphere

Clouds that shine at night

How do these glow-in-the-dark noctilucent clouds
form high in the Earth’s atmosphere?

How noctilucent clouds form Scattering Nucleus

After dusk, sunlight can still reach These ice crystals need
the mesophere - the coldest part of to contain some kind of
Earth’s atmosphere. The light hits nucleus to effectively
ice crystal shards and is scattered, scatter the light. This
with the stratosphere absorbing red could be either meteorite
light, leaving only blue. or volcanic dust.

Observing Temperature

The light from the Sun Ice crystal shards form
that hasn’t been when the temperature of
scattered by the ice the mesophere falls
crystals reflects into our below -120°C (-184°F),
eyes, illuminating the but this only happens in
noctilucent clouds. the months either side of
the summer solstice.
Sun sets
117
Once the Sun is more
than six degrees below
the horizon from the
perspective of the viewer,
it sends sunlight up into
the mesosphere, 80km
(50mi) up.

SCIENCE OF WEATHER Mammatus clouds can © DK Images; Dreamstime
pile up to great heights,
Mammatus clouds / Dew forming an anvil shape

Mammatus clouds Dew usually forms overnight
when the ground cools
Why these distinctive clouds may warn of tornadoes…

Clouds form when the atmosphere
becomes saturated and moisture
condenses out around tiny particles of
dust, salt or ice, collectively referred to as
condensation nuclei. The shape of the cloud
reflects the turbulence of the atmosphere and
signals what is happening with the weather.
Mammatus (or mammatocumulus) clouds
are puffy and rounded, with a distinctive
protuberance on their undersides. Their name
reflects their appearance, coming from the
Latin word for breasts, while ‘cumulus’ is the
Latin for pile or heap. Their formation is not
fully understood, but it is thought that they are
the result of sinking air, usually after a storm.
If a bad storm is brewing, clouds often pile
up high; the top of the pile drifts in the strong
winds of the upper atmosphere so the pile
becomes shaped like an anvil. This kind of
cloud is called cumulonimbus and it can warn
of torrential rain or snow, hail, thunderstorms
or even tornadoes to follow. Mammatus clouds
often form the underside of cumulonimbus
clouds and so are associated with storms.

How is dew
formed?

Discover why these sparkling
drops appear on the ground

Glinting dewdrops are a familiar sight
for early risers in the morning, but
dew is not a sign of overnight rain.
These picturesque water droplets are actually
formed when water vapour in the air comes into
direct contact with cold surfaces. This is why
dew usually forms overnight, as surfaces on the
ground will cool due to a loss of infrared
radiation from the Sun. You’re more likely to
notice dew after a calm, cloudless night too, as
cloudy skies help insulate the Earth and enable
surfaces, where dew would otherwise form, to
retain some level of heat.

118

RECORD 720km BIGGEST VON KÁRMÁN VORTEX STREET
BREAKERS
The longest Von Kármán vortex streets are usually to be found streaming
A LONG STREET from the Hallasan Volcano on South Korea’s Jeju Island. The longest one
measured to date ran for an incredible 720km (450mi) before it broke up.

DID YOU KNOW? Bees have been found to make use of vortices by taking advantage of energy created by the swirling eddies

What are Von The man behind
Kármán vortices? the mystery

The science behind these Von Kármán vortices being created Theodore von Kármán was born in © Corbis
mind-boggling, swirling by the island of Madeira and the Budapest, Hungary, on 11 May
cloud formations revealed Canary Islands in the Atlantic 1881. His father, a philosophy and
education professor, made him
The area of fluid dynamics is one in practise subjects such as
which scientists are still getting to geography and history. However,
grips with, but back in 1911, a Von Kármán’s natural maths
Hungarian called Theodore von Kármán ability shone through and he won
worked with a flow tank to demonstrate the the prestigious Eotvos Prize,
effect that a stationary body can have on the which was awarded to the
flow of a fluid passing over and around it. country’s best
As the fluid flow, such as a cloud formation, maths and
is disrupted by a cylinder – in nature this is science
generally an island or group of islands – the student.
fluid is forced to either side of the barrier. The
fluid flows around the obstruction, forming a He made
boundary layer close to the object, which hugs his famous
it closely. As the flow continues, the boundary breakthrough
layer becomes a shear layer, which continues while working
to move away from the barrier. If there is any as a
kind of pressure imbalance coming from privatdozent
either side of the barrier, the side with greater (university lecturer)
pressure forces the fluid flow upward, in Göttingen in Germany.
separating it from the main flow and causing a
swirling eddy. Having broken off one stream, 119
the cloud then folds back on itself, causing the
side with more pressure to be cut off and swirl
away in the opposite rotational direction,
creating a vortex.
As the flow continues, the alternation of
pressure imbalances continues, generating
what is known as a ‘street’ of repeated vortices
swirling in different directions (see image),
pushed along by the fluid flow.
However, not all fluids that meet a barrier
result in a Von Kármán vortex street. The
pressure imbalance is measured by using
Reynolds numbers, which represent the ratio
of moving forces to stationary forces in a fluid
flow. The higher the Reynolds number, the
more likely a fluid flow will be turbulent rather
than laminar (ie a smooth flow).
This phenomenon is most commonly seen in
clouds as they are pushed along by the air
current and disturbed by high-above-sea-level
islands and mountains, but they can also be
observed in the ocean and on ice.

SCIENCE OF WEATHER © Thinkstock

Freezing waterfalls

How do waterfalls freeze?

Some waterfalls look as if they froze mid-flow, but how is this possible?

Ice forms on still bodies of fresh water like lakes
when the temperature hits 0 degrees Celsius (32
degrees Fahrenheit) or below, but the physics of
freezing becomes a lot more complicated in moving water.
Waterfalls don’t immediately stop flowing and freeze over
when the temperature plummets to freezing point. Quite the
opposite, in fact. For a start, because the moving water is
constantly mixing, the entire waterfall will cool uniformly,
so it will take far longer for any noticeable change of state
compared with still water under the same conditions.
The temperature of the water in the river/stream and
waterfall it supplies drops slightly below freezing and
supercools, which causes the water molecules to slow and
begin to stick together to form solid particles of frazil ice.
These are tiny discs roughly one millimetre (0.04 inches) in
diameter, yet this is enough to start the freezing process.
The frazil ice discs will clump together when they come
into contact with one another, as well as sticking to nearby
surfaces. In the case of waterfalls that flow down the face of a
cliff, the discs will accumulate against the cold rock, while
for a free-falling waterfall, ice will cling to the overhang.
Eventually the frazil ice will form an anchor from which it
will grow and, provided the temperature of the water is
sufficiently cold enough for long enough, it will create a
column that runs the length of the waterfall. Over time, the
river or stream will completely freeze over leaving an icy
snapshot of the waterfall, eerily frozen in time.

The science of freezing

Traditionally we are taught that water freezes at 0 degrees
Celsius (32 degrees Fahrenheit), but in reality it’s nowhere near
as simple as that. Once the correct temperature has been
reached, ice crystals must nucleate for ice to form: either
clinging to a central body that’s another ice crystal or a foreign
particle. The rate at which this happens is dependent on a
number of factors, including the amount of movement in the
water and wind on the surface – both of which can slow ice
formation. Atmospheric pressure, a layer of insulating snow
sitting on top of a thin layer of surface ice, minerals in the
water and many other factors all affect the freezing process.

120

© Christian Thiergan

Why do we get What is the
red sky at night? wind-chill factor?

Just how true is the famous phrase, and Why does this phenomenon make it
what causes the sky to turn red? feel colder than it really is?

A red glow can often appear in the sky at dawn or dusk. The The wind-chill factor describes the rate at which your body loses heat
reason behind this red tint is a simple one, related to how light due to wind and low temperatures. When it’s chilly outside you will of
travels from the Sun up into the sky at this time. The low position course feel the cold. However, when fast-moving air (ie wind) blows
of the Sun, coupled with the thick layer of atmosphere the light must across your exposed skin you will feel even colder. This is because as wind
travel through, cause short wavelengths to scatter. Only the longest speed increases, the rate at which heat is carried away from the body also
wavelengths make it through, explaining why we only see a red increases, first causing an external temperature drop, then later – and more
colour displayed. dangerously – a reduction in internal body heat.
‘Red sky at night, sailor’s delight’ came into use before scientific weather The NOAA’s National Weather Service’s windchill index shows the serious
forecasting was developed. It is based on the assumption that weather implications. For example, if the temperature is -18 degrees Celsius (0 degrees
systems generally move from west to east, a red glow at night, indicating a Fahrenheit) and the wind speed is 24 kilometres (15 miles) per hour, the
clear sky in the west, therefore suggesting that bad weather systems have wind-chill factor would be -28 degrees Celsius (-19 degrees Fahrenheit) and
passed through. human skin would experience frostbite in just 30 minutes.

The smell of rain © Thinkstock

Find out why precipitation creates a distinctive
aroma that’s the same all over the world

It’s possible to smell rain before it has even fallen.
Lightning has the power to split atmospheric
nitrogen and oxygen molecules into individual
atoms. These atoms then react to form nitric oxide, which in
turn can interact with other chemicals to form ozone – the
aroma of which is a bit like chlorine and a specific smell
we’ve grown to associate with rain. When the scent carries
on the wind, we can predict the rain before it falls.
Another smell associated with rain is petrichor – a term
coined by a couple of Australian scientists in the mid-
Sixties. After a dry spell of weather, the first rain that falls
brings with it a very particular aroma that is the same no
matter where you are. Two chemicals are responsible for the
production of this indescribable odour called petrichor. One
of the two chemicals is released by a specific bacteria found
in the earth; the other is an oil secreted by thirsty plants.
These compounds combine on the ground and, when it
rains, the smell of petrichor will fill your nostrils.

121

SCIENCE OF WEATHER

Cave weather

Cave weather

Explore one of China’s most stunning cave systems
to learn why it has developed its own microclimate

Cut off from the Sun, rain and wind 6 million cubic metres (211.9 million cubic feet).
that we experience on the surface, you Once in an open chamber this humid air rises.
might assume meteorological
conditions in caves never change. However, While there are numerous entrances into
the reality is that their climates do vary this subterranean complex, exits are few and
significantly – not only from location to far between. In Cloud Ladder Hall’s case, it’s a
location, but within individual caves over time. hole in the roof some 250 metres (820 feet)
Indeed, some examples, like the Er Wang Dong above the floor, leading to a bottleneck effect.
cave system in Chongqing Province, China As the damp air hits a cooler band near the
(main picture), even host their own weather. exit, tiny water droplets condense out to create
Ultimately this is because very few caves are wispy mist and fog. In other chambers plants
100 per cent cut off from their surroundings. and underground waterways can also
In the case of Er Wang Dong, it all comes contribute to underground weather.
down to an imbalance in the local topology.
There are several tunnels around the cave Even caves without any direct contact with
system’s perimeter where wind can blow in. the outside world can still experience climatic
Once trapped underground air from outside variations, as they are subject to fluctuations in
gains moisture, pooling into huge chambers atmospheric pressure and geothermal activity,
like Cloud Ladder Hall – the second-biggest where the heat from Earth’s core emanates
natural cavern in the world with a volume of through the rocky floor. However, in such
caves, changes are more evenly distributed so
take place over longer time frames.

Here, fog clouds can be seen Area
in the deep sinkhole at the
entrance of the caves while 7 football
the Sun shines above it pitches

Sizing up Cloud Height
Ladder Hall
2.5 Statues
122 of Liberty

Volume

5 Wembley
Stadiums

RECORD 10mn m3 BIGGEST UNDERGROUND CHAMBER
BREAKERS
The Cloud Ladder Hall is only beaten by the Sarawak Chamber in Borneo
KING OF THE CAVES in scale. Sarawak is estimated to have almost double the volume of the
Chinese cavern, in the range of 10mn m3 (353.1mn ft3).

DID YOU KNOW? Although previously mined, the Er Wang Dong cave system was only properly explored for the first time in 2013

© Robbie Shone

123

SCIENCE OF WEATHER

Ozone layer

The ozone The structure
of the Earth’s
layer explained atmosphere
Here’s how the ozone
extends from the
Earth’s surface
Tropospheric ozone
We may hear about it a lot, and mainly how we’re slowly
destroying it, but just what is the ozone layer? Starts at ground level, with an altitude
of up to 15 kilometres. Energy transfer
The ozone layer is essentially Mother Earth’s populace, who would be exposed to an increase in from the surface heats it.
safety net, residing some 50 kilometres above skin-related diseases such as cancer. The lowest part of this is the
the planet’s surface. Created from O3, or ozone warmest with temperature
gas, it is up to 20 kilometres thick and 90 per cent of this So how does the ozone protect us? Ozone molecules decreasing with altitude. This
gas can be found up on the Earth’s stratosphere. This consist of three oxygen atoms, hence the chemical heat and CFC intervention
protective gas is vital to the nurturing of life on our planet, formula O3. Stratospheric ozone absorbs UVB high-energy produces turbulent diffusion,
and here’s why. radiation, as well as energetic electrons, which in turn producing great levels of
Ozone gases act as a shield against ultra violet, or UVB, splits the O3 into an O atom and an O2 molecule. When the ozone, harmful to organic
radiation. These harmful emissions are sent through the O atom soon encounters another O2 molecule they life.
Sun’s rays, and without the ozone would severely affect re-merge and recreate O3. This means that the ozone layer
the planet’s ecological balance, damaging bio-diversity. absorbs the UVB without being consumed. The ozone 5 10 15 20
UVB rays reduce plankton levels in the ocean, layer absorbs up to 99 per cent of the Sun’s high frequency
subsequently diminishing fish stock. Plant growth would UV light rays, transforming this into heat after its Altitude (km)
also diminish in turn disrupting agricultural combustible atomic reaction, therefore creating the
productivity. This would in turn affect the human stratosphere itself. This effectively incubates life on Earth. Typical cloud altitude

A whole lot of hole But ozone doesn’t reside only in the world above. Stratospheric ozone
This gas is also present in the layer around the Earth’s
The area of depletion over surface. Ten to 18km above us, this is known as the Between ten and 50
the Antarctic, known as tropospheric ozone or ‘bad ozone’, comparative to the kilometres up from the
the ozone hole, is stratopause. It contains up to
estimated at between 21 function of the stratosphere. This ozone occurs 90 per cent of Earth’s ozone.
and 24 million square naturally in small doses, initiating the removal of The stratosphere contains the
kilometres – enough to fit hydrocarbons, released by plants and soil, or highest level of ozone on the planet,
England in 161 times over! appearing from small amounts of with two to eight parts per million.
stratospheric ozone, which occasionally This reacts with UVB to produce
migrate down to the Earth’s surface. what we know as the ozone layer.
However, it gets a bad reputation due The stratosphere is layered in
to its interaction of ultraviolet light, temperature due to UVB absorption.
with volatile organic compounds Heat increases with altitude, with the
and nitrogen oxides, emitted by top of the stratosphere has a
fossil-fuel powered machines and temperature up to -3°C.
internal combustion engines.
This produces high levels of
ozone, which are formed in
high temperature conditions,
ultimately toxic to all forms of
organic life.

How big is the
hole in the
ozone layer?

© NASA The ozone hole refers to an area of depletion over the Antarctic region of Earth. The
planet’s ozone records a decline of four per cent per decade in total volume but
much larger loses are recorded in the stratospheric ozone over Earth’s polar region,
however this is seasonal condition. These areas’ unique atmospheric conditions see the
most impact. Strong winds blow around the continent forming a polar vortex, isolating
the air over Antarctica from the rest of the world. This allows special polar stratospheric
clouds to form at about 80,000 feet altitude. These concentrate atmosphere pollutant. When
spring returns after the sunless winter period the ozone is depleted causing the ozone hole. The
largest ever recorded ozone hole occurred in 2006, at 20.6 million square miles. At present the
ozone hole is recorded at between 21 and 24 million square kilometres.

124

How has Antarctica’s
ozone hole changed?

Find out what triggered the colossal ozone hole to form

The destruction of the ozone layer is widely Ozone damage is caused by chlorofluorocarbons, chlorine atoms into the stratosphere, starting a
recognised as one of Earth’s most troubling or CFCs, which were once used in fridges and aerosol process that will result in the destruction of ozone
environmental issues. Of particular concern cans. CFCs are incredibly stable in the atmosphere molecules. A strong catalytic reaction takes place,
is the hole that has formed in Antarctica’s ozone and are able to persist for years. This enables them to enabling a single chlorine atom to destroy
layer, which was first observed during the 1970s and reach the stratosphere where they do their damage. thousands of ozone molecules, as once the reaction
continued to grow until 2006. This is not an actual During Antarctica’s long winter months, the is complete the chlorine is released unchanged, free
‘hole’, it is simply an area of seriously depleted ozone stratosphere’s temperature plummets to less than to destroy even more ozone. If the 1987 Montreal
which has a value of 220 Dobson Units (a measure for -78 degrees Celsius (-108 degrees Fahrenheit), Protocol banning CFCs had not been introduced, it is
ozone density) or less. The cut off point is set at this causing clouds of ice to form and trap chlorine- thought that Antarctica’s ozone hole would be 40 per
value because readings lower than 220 Dobson Units containing compounds. Once spring returns in cent larger and another hole would have opened up.
had not been recorded prior to 1979. September, the Sun’s ultraviolet light frees the It is hoped to fully recover by 2070.

Ozone damage through the years

The growth of Antartica’s ozone layer is clear to see in these yearly observations

First observations 1979 1980 1981 1982 1983 1984 Ozone depletion

The ozone hole was first When scientists observed
measured by satellite in the ozone hole in 1980,
1979 and from here on the they could clearly see
extent of the damage was that it had grown in size
recorded in autumn each since the previous year.
year, when the maximum
damage is visible. No data

Taking action 1985 1986 1987 1988 1989 1990 In 1995, there were no
1991 1992 1993 1994 satellites in orbit that
In 1987 the Montreal 1997 1998 1999 2000 1995 1996 were able to collect the
Protocol had been
agreed upon by the 2001 2002 necessary data.
UN; CFCs would be
phased out. Unusually small

Continued In 2002, the ozone layer
depletion was half the size it was in

Throughout the late 2000. This was due to
1990s and early 2000s, abnormally warm
the ozone hole continued conditions in the
to grow, due to CFCs’
ability to remain present stratosphere, rather than
in the stratosphere. the ozone layer’s recovery.

Peak size 2003 2004 2005 2006 2007 2008 Will it recover? © NASA
2009 2010 2011 2012 2013 2014
In 2006 the ozone hole It is believed the ozone
reached its largest hole will eventually
recorded size; since
then it has remained start to shrink in size.
relatively stable. Levels of chlorine and
bromine are continuing
to reduce, which is an

encouraging sign.

125

SCIENCE OF WEATHER

Cloud types

Milky cirrostratus clouds Curling cirrus clouds High-flying cirrocumulus clouds

Cirrostratus clouds cover the sky like a Known as mares’ tails, these Appearing as a mass of small, thin puffs of
smooth thin veil and can create the high-altitude clouds are thin and cloud, cirrocumulus clouds develop at high
appearance of a halo around the Sun. wispy with a distinct curved altitudes between 6,100-12,190m (20,000-
They form high up between 5,490- shape. They appear in small 40,000ft) and are similar in formation to
9,100m (18,000-40,000ft) and indicate bands up to 12,190m (40,000ft) low-level altocumulus clouds. They are
that there’s moisture at high altitudes. above ground and are composed composed of ice crystals and supercool
of minute ice crystals. water droplets.
6,100m (20,000ft)
Vast altostratus cloud cover Cumulonimbus
Layered altocumulus clouds thunderstorm clouds
A thin but large cover of featureless
Altocumulus is a middle-level cloud that altostratus clouds develop between Cumulonimbus clouds have
forms between 1,980-5,490m (6,500- 2,130-5,490m (7,000-18,000ft) above low-lying dark bases that usually
18,000ft) above the ground. Its formation Earth. They diffuse sunlight so shadows form between 335-1,980m
varies between large patchy layers and won’t appear on the ground. (1,100-6,500ft). They are known
spaced out flat or wavy shapes. They as thunderstorm clouds and are
consist of cool water and ice crystals and associated with lightning,
often indicate a coming change in weather. thunder, heavy downpours of rain
or hail and even tornadoes!

Cloud-spotting guide
Find out what causes clouds to form and learn how to
identify the most common types in our atmosphere

Dense stratus clouds Floating cumulus clouds 2,000m (6,560ft)

Stratus clouds provide a Puffy cumulus clouds resemble Patchy stratocumulus clouds
blanket of grey or white cloud cauliflowers and their bases form
cover and can at times up to 1,980m (6,500ft) above the Stratocumulus clouds spread like a
appear low on the ground as ground. They are usually seen in shallow patchy sheet across the sky.
a form of fog. They are also fair weather and if they continue to They are low-lying clouds and are formed
usually accompanied by grow in size, they will become by shallow convective currents in the
drizzle or snow. thunderous cumulonimbus clouds. atmosphere. Their presence indicates
light precipitation and they are usually
seen before or after bad weather.

© The Art Agency

126

Why are clouds white?

Discover the basic scientific principle Base Source
that makes clouds white
The amount of light that The Sun sends out rays of white
Clouds are formed when humid air, or water vapour, penetrates to the base depends light which take just over eight
rises and cools. The vapour expands and becomes tiny on the thickness of the cloud.
droplets. Clouds only get their white appearance if minutes to reach Earth.
these droplets become large enough to scatter visible light in all
directions; this is known as Mie scattering. Mie scattering
Visible light is a form of electromagnetic radiation, with
each different colour that we can see having a different If the water droplets are large
wavelength. White light, however, contains equal amounts enough, the white light is
of all colours of the spectrum. When sunlight hits the scattered in all directions.
individual water droplets in a cloud all wavelengths of light are
scattered evenly in all directions. However, very thick clouds,
which are made of very densely packed water droplets, will
appear darker – like storm clouds – because less of the
incoming light from the Sun can penetrate to the base. From
above in an aeroplane, though, a storm cloud will still appear
white – it only looks dark from the ground because little
sunlight is not getting through.

The rain 3. Condenses 4. Precipitates 5. Sinks 6. Rain shadow
shadow
effect As the air rises it cools The windward slope of Cool, dry air sinks Because the air has lost its
causing the water the mountain receives and warms on the moisture in earlier
vapour in the clouds precipitation as the leeward side,
to condense and turn vapour condenses. downwind of precipitation, the region
into rain. the mountain. behind the mountain sees

very little rainfall.

1. Prevailing wind 2. Rises © Science Photo Library

The wind pushes warm, water-filled clouds The warm, moist
towards the windward side of a mountain. air rises up the
mountain barrier.

Rain shadows Whydoesthisweather
phenomenon cause deserts to
form on one side of a mountain?
A rain shadow is an area that Such an obstruction blocks the path Essentially this means that the contrast of conditions with the
receives very little of moisture-rich rain clouds. Due to a windward side of a mountain receives formation of a desert on one side but
precipitation due to a process of cooling and condensation, a plenty of precipitation where as the not the other. The warm, dry breeze
substantial obstruction, most shadow area of dry conditions is likely leeward side might be left extremely that blows down the leeward side of a
commonly a large mountain. to develop beyond this barrier. dry. This can result in a dramatic slope is known as a foehn wind.

127

SCIENCE OF WEATHER

Rain / Fog

Why, and 4. Rain forms 5. Rain falls
how, does
it rain? As more water vapour droplets gather within the Sometimes water will not make it back to
cloud, they start to merge and become larger. Earth, due to the air not being humid enough,
In England, rain is a more common Eventually they will become too heavy to be held in the
occurrence than most of us would atmosphere and gravity will start to pull them back and in this case, water evaporates back into
like, but it is very important for the towards Earth. the atmosphere. If the temperature of the air is
maintenance of our ecosystem
3. Clouds form lower than normal, the water will freeze and
Rain is defined as liquid precipitation. It is formed fall as snow or hail instead of rain.
high above the ground in clouds by water vapour When the water vapour droplets
coming together into large droplets that become too reach a certain level, condensation 6. Water
heavy for the air to support. Gatherings of condensed water starts to occur, forming clouds. This returns to
vapour are called clouds, and this is where rain comes from. is due either to an increase in the Earth
Although a large amount of water is held in each cloud, rain humidity or a drop in temperature in
does not fall all at once from the cloud because the water the atmosphere. If the water that falls is not
droplets grow at different speeds, with the fastest growing caught by plants or animals, water
droplets becoming heavier quicker and falling first, the slower 2. Water hits the ground and, if not evaporated
growing ones falling after. vapour from the land, it will start to move back
Although scientists are not sure if there is water on other travels towards rivers, streams and the sea – where the
planets, the phenomenon of rain has occasionally been
recorded. This rain involves other liquids, such as methane The heat from the process begins again.
which falls on Titan, Saturn’s moon, and sulphuric acid which Sun pulls these
falls on Venus. water vapour
droplets upwards
into the
atmosphere.

1. Water
evaporates

Water on the Earth’s
surface is heated by the
Sun, and small water
droplets evaporate into
the air.

What are fog, DID YOU KNOW? © Milazinkova 2009
mist and haze?
The ‘Asian brown cloud’ is a
Discover how fog lets you walk through the wintertime pollution haze
clouds without leaving the ground over parts of Asia. It’s big
enough to see from space.
Fog and mist are ground-level clouds: they are formed of airborne water
droplets. Fog is denser than mist – it prevents you seeing further than
1km ahead. In mist, you can see between one and 2km. Haze also makes
the air less clear. But unlike mist and fog, it’s caused by airborne particles of soot, salt
or dust.
Fog and mist form when moist air near the ground cools enough that condensation
occurs. Condensation is the mechanism that mists a mirror when you breathe on it. Air
contains water vapour – the warmer the air, the more vapour it can hold. When the
warm air in your breath hits the colder mirror, it cools. The vapour the air can no longer
hold condenses out, ie water droplets form on the mirror’s surface. Haze particles can
be a precursor to fog because, in fog, water droplets form on particles in the air.

128

Double, or multiple, rainbows
are only visible to the naked eye
when the incoming sunlight is
unhindered by atmospheric
effects, so is very intense

Double rainbowsWhatcausesthiscolourful
meteorological phenomenon?

Regular rainbows occur when moisture in the angle of refraction, a different colour of light will the light but undergoes the same refraction, so exits
the air – commonly rain, but also mist or be reflected outwards; the result of this process is in the same way as before – though upside down.
spray such as that from a waterfall – what we observe when we see a rainbow.
refracts sunlight in such a way that it is broken up This second reflection reduces the intensity of the
into its constituent colours. Every rainbow is accompanied by another, sunlight, but it also produces a second inverted
The phenomenon occurs when the Sun is secondary rainbow, but it’s usually too dim to see. rainbow, creating a double arc of multicoloured light
positioned behind you and sunlight passes through This double rainbow effect is due to the continued in the sky. Interestingly, sunlight can reflect many
the airborne water. The light refracts (bends) inside reflection of light inside each water drop. Sunlight is more times inside a water drop so many more
the droplets and the white light is broken up. Each actually reflected twice inside a drop: once to rainbows (three, four or even more) can be
colour has a different wavelength so, depending on produce the primary rainbow and a second time at produced, but the incoming light is rarely strong
the back of the drop. This second reflection inverts enough for these to be visible by the naked eye.

Double Primary A double rainbow above the
rainbow Krimml Waterfalls in Austria
formation The primary rainbow
forms through the
Angle refraction of sunlight
within raindrops.
The angle at which the
light is emitted Secondary
determines what colour
will be visible, ranging If the incoming light is
from red at 43 degrees strong enough, a faint
to violet at 40 degrees. secondary rainbow will
be observable.
© SPL Upside-down rainbow “Every rainbow is
Alexander’s accompanied by
The inversion changes the angle dark band another secondary
at which the coloured light is one, but it’s usually
emitted, ranging from violet at 54 The region between the too dim to see”
degrees to red at 50.5 degrees. two rainbows appears
dark as no light
reflected here is visible
to the viewer.

129

SCIENCE OF WEATHER

Why is snow white?

Why is snow white?

Have you ever wondered how snow is white? It’s all
down to the refracted light

To answer this question there are two things which
need to be considered – colour theory and refraction.
Refraction is the change in direction of light as it goes
from one material to another. It is due to a slight change in speed
of the light and it explains why straws look bent in water. When
light enters snow, it refracts. This is because snow is made from
lots of ice crystals tightly packed together, the important fact here
being that these crystals are translucent (light can pass through
but not in a direct path – it changes direction). Additive colour
mixing tells us that if we combine all of the frequencies of colours
we get white light. When light falls on snow it is composed of a
mixture of different frequencies which all refract slightly
differently as they enter the ice crystals. Eventually due to
refraction, the light leaves the surface of the snow in all directions
and hits our eyes. This light is composed of a mixture of
frequencies which our eyes detect as white light.

130

1. HIGH Cumulus 2. HIGHER Altostratus 3. HIGHEST Cirrus

HEAD These small clouds that A blue or greyish cloud Found at altitudes of up to
look like bits of cotton formation, altostratus a lofty 12,200m
2HEAD wool don’t ever soar clouds are found at a (40,000ft), cirrus clouds
above 1,980m (6,500ft) height of between 2,130m take on and reflect the red
HIGHEST CLOUDS in the sky, which is still (7,000ft) to 5,500m colour of the sunset you
higher than some others. (18,000ft). see at dusk.

What are lenticular clouds?

Explore the cloud formations that look suspiciously like UFOs

Height Shape Movement

A huge amount of ‘wave The shape is a distinctive Due to being made up of
lift’ is caused by the saucer structure caused by mostly vertical wind flow
topographic barrier of a the vertical wind flow in (known as vertical
mountain so these types of the centre of the oscillations), the clouds
cloud form thousands of motionless cloud. stay very still and can
feet in the air. often form into stacks.

Airflow Location

Originating from a strong Lenticular clouds form
wind, airflow is always almost exclusively near
very rapid in a lenticular mountains and hills. When
cloud, making it great fun a strong wind is
for hang gliders but not so interrupted by a tall
good for aircraft, which landmass, a wind-wave
avoid them at all costs! pattern is created.

The poles Rising high

Particles travel along The aurora borealis
Earth’s magnetic field tends to sit 100-400km
lines to the poles. Here (62-250mi) in the air.
they are deflected into
the upper atmosphere. Colours

Atmospheric gasses As the particles and
gasses react, different
The gasses in our colours are given off,
atmosphere such as oxygen depending on the gas
and nitrogen react with the that’s being hit.
charged particles.
Solar winds Conditions
Aurora
borealis Charged particles are To be able to see the
fired toward Earth by aurora borealis, you
The jaw-dropping lights that solar winds. need a clear sky and
brighten the night sky explained a lot of solar activity.

131

SCIENCE OF WEATHER

The nitrogen cycle

Essential to organic life, Nitrogen
nitrogen makes up most
of the Earth’s Lightning
atmosphere. It is a major
component in the building of Volc
protein in cells, and is vital in the
production of amino acids. Urine
However, we cannot obtain
nitrogen, as a gas, directly from Assim
the soil or air without it being
combined with another element, 1. Nitrogen fixation Dead animals 4. Decay
and so it must go through a series and plants
of four natural chemical reactions This process makes atmospheric When an animal or plant dies,
– nitrogen fixation, nitrification, nitrogen compounds available to plants Decomposers its waste matter (made up of
denitrification and decay – by constantly converting the gas into and ammonification organic nitrogen compounds)
known as the nitrogen cycle. ammonia. Nitrogen-fixing returns to the soil. The
Understanding the stages of the microorganisms in the soil fix bacteria and fungi that
nitrogen cycle can seem atmospheric nitrogen gas to ammonia decompose the dead animals
complicated because nitrogen in a reduction reaction. Nitrogen and plants convert this
can exist in several different fixation can also occur as a result of organic nitrogen (found in the
forms. While food-making lightning: the massive amount of proteins and urea) into
organisms get the nitrogen they energy produced by a bolt enables inorganic ammonia and
need from nitrogen fixation and nitrogen in the atmosphere to fix to ammonium compounds in
nitrification, animals and nitrates in the soil. the soil.
humans don’t make their own
food and so must eat plants or Ammonia N
animals that eat plants to get
their fill.
First, let’s take nitrogen
fixation. Although there is a vast
amount of nitrogen gas in the
atmosphere, it must be fixed – or
put into a biologically useful
compound – for living organisms
like us to be able to use it. Only
then can it start to move through
the ecosystem. Fixation starts off
when bacteria convert nitrogen
gas into ammonia in the soil.
Special plants known as legumes
also have certain bacteria in their
roots that make this possible.
Once in the soil, the nitrogen
becomes biologically accessible,
and nitrification is the process
that takes nitrogen fixation one
step further. Specialised bacteria
use oxidation to convert
ammonia into nitrite, and nitrite
into nitrate, which plants can
incorporate into their tissues.
During what’s known as
denitrification, plants take
nitrogen from waterlogged soil by
absorbing nitrates and
ammonium ions, turning them
into organic compounds.
Nitrogen compounds are also
returned to the soil through
animal waste and decaying
plants and animals.
Although the most abundant
form of nitrogen is obviously the
air around us, the processes
through which nitrogen gets into
the rest of our ecosystem are
essential for the circle of life.

132

5 TOP The invisible element Liquid ice Big bangs Breathe easy Colourful effects
FACTS
1 Nitrogen is colourless, 2 When nitrogen is cooled to 3 Nitrogen is even used in 4 Nitrogen gas makes up 78.08 5 Nitrogen is responsible for
NITROGEN odourless and tasteless, and below -196°C it turns into a explosives such as TNT. The per cent of the Earth’s the orange-red, blue-green,
although practically inert at liquid that can freeze a chemicals used in this kind of atmosphere; the rest is 20.95 blue-violet, and deep violet
normal temperatures, when substance in seconds. Handy nitrogen compound break per cent oxygen, 0.93 per cent colours that are visible with
altered it can be used for foods, in medicine for transporting apart releasing huge argon, 0.038 per cent CO , plus the aurora borealis (the
fertilisers and poisons. blood and transplant organs. quantities of gas. 2 northern lights).
traces of other gases.

DID YOU KNOW? Harvesting plants before they die means soil requires fertilisers containing nitrates or ammonium compounds

cycle Weexplainhowliving
organisms make use of the most
abundant gas on the planet

Atmospheric Emissions from Synthetic
nitrogen N2 industrial combustion nitrogen fixation
and gasoline engines
Rain Although the nitrogen cycle is a natural phenomenon, we
cano humans can affect things. For instance, the Haber-Bosch
process, which is used in the industrial production of ammonia
for fertiliser, contributes to the total fixation of atmospheric
nitrogen. The Haber-Bosch process directly combines nitrogen
from the atmosphere with hydrogen under high pressure and

fairly high temperature, which, together with a
catalyst such as iron, produces a reaction not
possible at lower temperatures. The lower
the temperature and the higher the
pressure, the more ammonia is produced.
Haber-Bosch remains one of the most
fundamental processes in the chemical
industry today.

milation Fossil fuels

NH3 Fertiliser

Nitrates NO3- 3. Denitrification
Nitrites NO2-
As you would imagine, denitrification is the
opposite of the combined processes of nitrogen
fixation and nitrification, and it takes place in
waterlogged soils. Denitrifying microorganisms
(bacteria) convert inorganic nitrogen (nitrates) into
small quantities of nitrogen gas, which is then
released back into the atmosphere.

2. Nitrification Natural activities
Human activities
Nitrification, which is only possible if the soil conditions are not too
waterlogged, acidic or cold, converts ammonia in the soil into nitrates. 133
While ammonia is the primary product of nitrogen fixation, the
conversion of ammonia to nitrites and nitrates (carried out by nitrifying
bacteria) is nitrification. Plants absorb the nitrates and use them to
make proteins.

SCIENCE OF WEATHER

Cloud formation

Influencing cloud
formation Weexploreelementalfactors

influencing varying cloud types

Look up into the sky above and you will at a rate of approximately ten degrees Celsius per There are several cloud formations at high
notice that clouds constantly shift in shape every 1,000 metres, until saturation occurs. Stratus altitude. Most notable are cumulonimbus, which
and size. This is due to there being clouds, for example, form when minimal upward form if cumulus congestus clouds continue to
numerous common types of cloud formation, with vertical air currents lift a thin layer of air high, grow vertically. Ranging from near ground level
each performing a natural role, which is determined which is enough to initiate the condensation of up to 50,000 feet, this formation releases
by external factors such as altitude, condensation excess water vapour. enormous amounts of energy by condensated water
and disposition. These include stratus, cumulus, vapour. Lightning, hail and violent tornadoes are
stratocumulus, altocumulus, cirrus, cirrocumulus Altocumulus clouds are part of the middle order associated with cumulonimbus clouds. During the
and cumulonimbus. of formations, appearing greyish with dark formation, condensation carries droplets up and
Most cloud formations are produced in patchy areas. Often these clouds precede a cold down several times before being released and
environments that are saturated, or where front, and on a warm humid morning indicate combining to form raindrops. In larger specimens
relative humidity is at 100 per cent. Varying approaching thunderstorm activity. Altocumulus up-currents become extremely severe, splitting
mechanisms can activate this process. For example clouds are often produced due to turbulent updrafts raindrops and ice crystals, before re-combining
orographic uplift, which occurs as air is forced up of air, uplifted by terrain barriers such as and falling to the ground. This contributes to a build
due to the physical presence of elevated landmass. mountains, composed of super-cooled water, below up of electrical charges and therefore the occurrence
As air rises it cools as a result of adiabatic expansion, freezing, which has not yet crystallised around a of lightning.
condensation nucleus.

Common types of clouds in the troposphere

Cirrocumulus Cirrus Cumulonimbus

Altitude: Above 18,000 feet Altitude: Above 18,000 feet Altitude: From near the
ground to above 50,000 feet
Altocumulus

Altitude: 6,000 to 20,000 feet

Altostratus

Altitude: Below 6,000 to 20,000 feet

Stratus

Altitude: Below 6,000 feet

Stratocumulus Cumulus

Altitude: Below 6,000 feet Altitude: Below 6,000 feet

134

Weather symbols
How to read and understand the symbols on a
weather map

Weather forecast centres around the world are Fronts
constantly analysing atmospheric conditions
on Earth. The public are then supplied with A weather front is the line on a map
this information in the form of pictographic maps dividing two air masses of different
detailing precipitation, cloud, wind speed/direction, densities. Here conditions will be
temperature, and frontal systems. unsettled. The symbols for fronts
are arranged on lines consisting of
Types of weather semicircles, triangles or a mixture
of the two.
The other symbols found on a weather map include the
various types of weather. The following classification Cold front
symbols are based on those the MET Office uses. There Associated with brief episodes of
are additional symbols for day and night variations… severe weather, and identified by a
blue line with triangles that point
Shape Main facet Main Symmetry Clear sky Sunny Sunny intervals in the direction of movement, a cold
branches Dust front marks the leading edge of an
The unique Water vapour Each branch MIST FOG advancing mass of cold air. Because
shape of a freezes on to a Each snowflake extends cold air is denser, it pushes the
snowflake is molecule of ice, develops six outwards at Mist Fog warmer air up where it condenses
dependent on creating a flat branches from exactly the into clouds and precipitation.
temperature surface called the central same rate as all Dense cold air also travels faster
and moisture. a facet. hexagonal facet. the others. than warm.

HAZE Medium-level cloud Low-level cloud Warm front
Slower-moving warm fronts are
Haze marked on weather maps as a red
line with semicircles that point in
Snowflakes Drizzle Light rain Heavy rain the direction of movement. These
represent the leading edge of an
How are these beautiful advancing mass of warm, moist air,
crystals of ice formed? bringing with it cloud, precipitation
and warm temperatures.

The formation of a way, creating six-way Thunderstorm Tropical storm Sleet
snowflake begins symmetry and a unique flake
when a microscopic every time. Hail Light snow Heavy snow Occluded front
cloud droplet freezes as a tiny This purple line of alternating
ice particle. Water vapour The first person to Temperature 12 triangles and semicircles denotes
that condenses on its surface photograph a snowflake was an occluded front, or occlusion,
causes the ice to develop flat, American Wilson Bentley. Temperature is shown as a figure (measured in degrees which forms when the faster-
polished surfaces, known as Bentley took his first Fahrenheit or degrees Celsius) depicted either by a moving cold front catches up
facets, which continue to snowflake snap in 1885, using number in a circle/square, or as an isotherm, which is a with the warm front, forcing
grow into a hexagonal prism a bellows camera and a line linking points of equal temperature. the less-dense warm air up above
shape. At each corner of the compound microscope, and the surface.
hexagon shape, new went on to assemble a large Wind 8
branches extend outwards collection of beautiful snow Stationary front
each at the same rate. All crystal images. Wind also features a figure that shows wind These stationary, or slow-moving
snowflakes have six sides and speed in miles per hour. This number is fronts represent the boundary
can be either prism-shaped, Here’s one accompanied by an arrow to indicate which between two air masses neither of
plate-shaped or star-shaped. I made direction the wind is travelling. which has the ability to replace the
As the snowflake moves earlier other. Stationary fronts are
around within the cloud, it Pressure 982 depicted by an alternating line of
encounters a variety of red semicircles and blue triangles
temperatures that change Atmospheric pressure is shown in the form of isobars, pointing in opposite directions.
the growth behaviour of which are lines of equal mean sea-level pressure. When Clouds and prolonged precipitation
each flake, causing the six there is a difference in air pressure, air is accelerated are associated with these fronts.
branches of the crystal to from high to low pressure, causing windy conditions.
grow in exactly the same

135

THE WEATHER
& USHow the human race interacts with weather

150

© Alamy

158

138 Controlling the weather 144 Predicting the weather 154 Ivanpah Solar Power
Find out how we can control How does the Met Office Facilty
the weather predict the weather? How doe this facility produce
power to used in our homes?
142 Wind tunnels 146 Michael Fish
How do engineers test aircraft We talk to the forecaster about 156 Power from the oceans
against wind speeds? his career at the Met Office Learn about the sustainable
energy produced
143 Measuring wind speed 148 Renewable and non-
Learn how to measure renewable energy 158 How flood barriers work
the speed of the wind with Get an insight into the future How are we able to hold back
an anemometre of energy generation large surges of water?

143 Sunblock 150 Solar power “The simple fact
How does sunblock contribute Charge your home with is that weather is
towards protecting your skin power from the Sun using unpredictable”
from UV light? solar panels

136

© Ivanpah SolarTHE WEATHER & US

144

154

156 138

Cloud-whitening barge © John MacNeill Illustration 137

THE WEATHER & US

Controlling the weather

CONTROLLING
THE WEATHER

DISCOVER HOW WE MAKE RAIN AND THE AMBITIOUS
PLANS BEING HATCHED TO TACKLE CLIMATE CHANGE

Superhero Storm in the X-Men comics cloud-seeding projects in at least 20 countries Weather Modification Inc, a private weather
can conjure rain, end droughts and worldwide, from Israel to Australia; in 2003, in control company based in North Dakota, USA.
create hurricanes with the power of the US alone, ten states were conducting at least
her mind. Now, scientists and meteorological 66 cloud-seeding programmes. In China, US enthusiasm for weather modification
technology are opening more and more around 32,000-35,000 people are employed in research waned in the late-20th century, with
opportunities for us mere mortals to the weather modification industry. funding falling to less than five per cent of its
manipulate weather and Earth’s climate. Seventies peak. But there are signs of fresh
In 2009, Chinese meteorologists from the The big question in cloud seeding is: how interest in the field. The US National Science
Beijing Weather Modification Office claimed to effective is it? A 2003 US National Academies Foundation (NSF) is funding a cloud-seeding
be responsible for the city’s earliest snowfall report concluded there was no concrete project in the Wyoming mountains, operated
since 1987. Around 16 million tons of snow scientific proof it worked. According to by Weather Modification Inc. New technology,
reportedly fell over drought-afflicted northern Professor Michael Garstang from the University such as advanced computer models and radar
China after workers fired rockets carrying of Virginia, who chaired the report, the instruments that can see inside clouds is
pellets of silver iodide into heavy clouds. situation hasn’t changed much since; there driving the resurgence of interest, says Boe:
The rockets were cloud seeding, a process remains “a lack of definitive evidence,” he says. “We’re bringing a lot of new tools to bear on the
invented in the late-Forties. Supporters claim it question. These tools weren’t available before
can reduce hail damage, increase rainfall and Even cloud-seeding supporters admit it and they’re starting to bear fruit.”
disperse fog among other things. There are doesn’t currently lead to a huge rise in rain and
snowfall. “It doesn’t increase precipitation by The Wyoming project, launched in 2005, uses
50 per cent in most cases,” says Bruce Boe from aircraft-mounted radar and ground-based

138

5TOP Geoengineering is ready One tech is enough It solves climate change We can’t create rain It’s all a conspiracy
FACTS
1 Today’s geoengineering ideas 2 No single ‘magic technology’ 3 Geoengineering doesn’t stop 4 There’s emerging evidence 5 There’s no scientific evidence
MYTHS BUSTED are untested or small-scale can cool the Earth. Future greenhouse gas emissions – that cloud seeding can make behind claims that HAARP, a
experiments. Cooling Earth by geoengineers might use many the root cause of man-made rain. An Australian project in US facility studying Earth’s
one degree Celsius would fixes, like reflective buildings, climate change. It’s a ‘plaster’, 2005-2009 found that rainfall ionosphere, is a secret
require a minimum five years of a space-based deflector and pausing harmful warming to increased in suitable clouds conspiracy for creating
military-scale effort. encouraging reforestation. give us time to cut emissions. by an average 14 per cent. hurricanes as weapons.

DID YOU KNOW? A global survey in 2010 found 72 per cent of us supported research into reflecting sunlight to cool the planet

instruments. It tests the effectiveness of cool down the planet. In the last few years, UK government-funded geoengineering
seeding winter orographic clouds – which are billionaire Bill Gates reportedly donated £2.8 research project: “We don’t know what the
cold clouds formed when air rises over million ($4.5 million) to geoengineering scale of unabated climate change will be,” he
mountains – with silver iodide. research, and the UN IPCC report, a summary of says. “You’ve got to think in advance what
what most scientists agree we know about emergency measures you might need, and then
”In the mountains of the American West, climate change, mentioned geoengineering for hope you won’t need them.”
these types of storms are the main target for the first time this year.
cloud seeding. Often the clouds are not efficient There are two types of geoengineering. Solar
at generating snow, so cloud seeding is used to Geoengineering is essentially ‘Plan B’ in case radiation management (SRM) cools the Earth by
enhance snow production,” says Dan Breed we reduce greenhouse gas emissions ‘too little, reflecting the Sun’s heat back into space, while
from the US National Center for Atmospheric too late’ to avoid dangerous climate change, carbon dioxide removal (CDR) scrubs CO2 – the
Research (NCAR), who is evaluating the project. argues a 2009 report by the UK’s Royal Society. A primary greenhouse gas causing man-made
temperature rise of just two degrees Celsius (3.6 climate change – from the atmosphere.
Another aim of the experiment is to increase degrees Fahrenheit) could melt the Greenland
snowfall by perhaps ten per cent a year, ice sheet and cause a long-term sea level rise of Examples of SRM include space mirrors,
building up the winter snowpack so it’s seven metres (23 feet). That’s enough water to injecting sulphate aerosols into the atmosphere
available for use. The extra water running off submerge both London and Los Angeles. through giant hosepipes and painting urban
the mountains each spring would be worth an roofs white. One idea uses cloud seeding to
estimated £1.5-3 million ($2.4-$4.9 million). To avoid this wide-scale warming, we’d need make clouds more reflective. Fleets of
to cut global carbon dioxide emissions by 50 per unmanned 3,000-ton barges could sail the
Cloud seeding affects the weather in a local cent of 1990 levels by 2050, according to the oceans, spraying clouds with saltwater. Salt
region, but there are other technologies being Royal Society. Yet emissions are still rising – by particles should create more water droplets in
devised to alter climate on a much bigger scale. 1.4 per cent during 2012. Even if we cut carbon the clouds, whitening them. Proposals for CDR
Space mirrors and giant floating hosepipes emissions today, temperatures will continue include fertilising tiny marine plants with iron,
might sound far-fetched, but they’re two rising for decades. The climate system is like an growing new forests or fast-growing crops and
proposals for geoengineering. Geoengineering oil tanker – ie slow to turn around. burying charcoal, all of which lock up CO2 and
is deliberate global modification of Earth’s remove it from the air. Most geoengineering
climate to counter man-made climate change. Dr Hugh Hunt is an engineer from Cambridge proposals remain in the lab at this stage.
University working on SPICE (Stratospheric “We can do very little right now because the
Geoengineering may sound impossible, but Particle Injection for Climate Engineering) – a
serious scientists are investigating how it might

Geoengineering plans
include ideas for orbiting
sunlight reflectors in space

Special barges could send Cloud-whitening barge © John MacNeill Illustration
up sea salt to whiten clouds
and help reflect sunlight
New technology has
led to a resurgence in
cloud-seeding projects

139

THE WEATHER & US

Controlling the weather

Weather-changing tech in action Volcano balloons 1 Helium balloon

Discover the machines and techniques capable of adapting Earth’s climate Hosepipes attached to giant helium A helium balloon the size
balloons would spray particles high of a football stadium is
Space mirrors into Earth’s atmosphere to mimic the attached to a hosepipe
cooling effect of volcanic eruptions. and tethered to a ship.
A giant sunshade made of For example, aerosols released by the
tiny mirrors could be put 1991 Mount Pinatubo eruption cooled 2 Tethered pipe
into orbit to cool the Earth. global temperatures by an average
Taking decades and 0.5°C (0.9°F). The proposed balloons The hosepipe pumps
trillions of dollars to would be the largest and tallest particles to 25km (16mi)
deploy, its effect on our man-made structures in history. above Earth’s surface –
weather is unknown and double the cruising
it would not stop the Reforestation height of your average
oceans acidifying. commercial airliner.
Regrowing trees in previously
Reflective buildings forested areas to increase the carbon 3
dioxide they absorb is cheap and 1
Painting roofs white and brightening roads/pavements safe, but conflicts with the
should help bounce the Sun’s heat back into space and cool ever-rising demand for agricultural
the Earth, but some scientists believe white roofs could land for food and energy production.
reduce cloud formation and increase warming.
2
Enhanced weathering
1
This would involve spreading crushed olivine – a silicate 2
mineral – over agricultural land, which chemically reacts
with CO to produce alkaline limestone; this could then be 3

2

used in the ocean to reduce acidity. A simple idea, but
would require huge mining and chemical plants.

Artificial trees

These towering machines would
scrub carbon dioxide from the air,
turning it into liquid that can be
stored in porous rocks beneath the
oceans. Millions of artificial trees
would be needed and the CO needs

2

storing for millions of years.

Reflective crops

Certain crops, shrubs and grass reflect
more sunlight back into space than
others. This would be cheap to
implement, but needs a huge land area
and has unknown effects on food
prices, plant growth, disease and
drought resistance.

Biochar

Biochar is charcoal produced by ‘cooking’
plants or manure with little or no oxygen. It is
decay-resistant and can store carbon in soil
for thousands of years. Useful on a small scale,
but growing biochar crops conflicts with the
demand for food and biofuel production.

technology hasn’t been developed to intervene technically possible,” continues Dr Hunt. “No legally. It needs lots of tanker ships, chemical
on a planetary scale,” notes Andy Parker. one has built a 20-kilometre (12-mile) pipe that plants and iron. “There’s nothing technically
goes vertically upwards.” Among his difficult about that,” says Professor Andy
Still, there are a few examples of outdoor field unanswered questions are, firstly, can we build Ridgwell from Bristol University.
tests. The SPICE project included a plan, later and launch a balloon big enough, and secondly,
abandoned, to pump water one kilometre (0.6 can we build a pipe strong enough? It would take hundreds of years to see results
miles) vertically through a pipe attached to a from iron fertilisation and other CDR
helium balloon. Its aim was to test the Other geoengineering proposals rely on technologies though. They rely on slow natural
feasibility of squirting sulphate aerosols pre-existing technology. Fertilising oceans processes, such as fertilising tiny marine plants
through a giant hosepipe 20 kilometres (12 with iron, for example, has already happened that transport carbon into the deep ocean when
miles) above the ground. “We don’t know if it’s on a small scale although not necessarily they die. “You can’t suddenly pull loads of

140

KEY 1891 1946 1952 1967 2008
DATES
Rainmaker Robert Dyrenforth Vincent Schaefer performs 34 die in a flood in Operation Popeye, a secret The Chinese government
MAN-MADE tries proving noise causes the first cloud-seeding
WEATHER downpours by exploding experiments, dropping dry Lynmouth, England. The UK US cloud-seeding project, tries to prevent rain at the
dynamite kites over Texas. ice pellets into clouds.
cloud-seeding Operation seeks to deluge enemy 2008 Beijing Olympics by

Cumulus is blamed. troops in Vietnam. launching 1,104 rockets.

DID YOU KNOW? Global temperatures could rise by more than 1°C by the end of this century, even if we reduce carbon emissions

3 Spray of particles 1 Clouds seeded Cloud seeding Can we stop
a hurricane?
The hosepipe squirts the particles Silver iodide or salt is Cloud seeding is a technique for man-
into the stratosphere, scattering sprayed into clouds from made rainmaking already used around the Hurricane Katrina in 2005 was arguably the
solar radiation back into space. a plane, with a rocket or world to varying degrees of success. worst natural disaster in American history, and
from a floating barge. Rainfall naturally occurs when water many scientists believe hurricanes will only
1 droplets attach to sand, dust or salt worsen with climate change.
2 Droplets form particles. Cloud seeding squirts extra
particles into clouds to spawn new So there’s no shortage of ideas for stopping
Water droplets attach to raindrops. Salt is used in warm tropical these devastating storms. In 2009, Bill Gates
the particles. Heat clouds, while silver iodide is added to cold backed a proposal to halt hurricanes by towing
released during droplet clouds to create extra ice crystals. tub-like barges into their path. These would cool
formation draws moist the warm ocean waters fuelling the storm.
air into the cloud, Some scientists believe cloud seeding
thickening it. can brighten clouds to counteract climate Most plans underestimate a hurricane’s power
warming too. The extra particles make the though; according to the NOAA Hurricane
2 clouds denser, whiter and more reflective, Research Division, one storm can release the
deflecting more sunlight back into space. energy of 10,000 nuclear bombs. For example, to
fight a hurricane with water-absorbent powder
3 Rain falls you’d need hundreds of planes to make sorties
every one and a half hours.
3 The droplets or ice crystals
collide, growing bigger and Some therefore argue that it’s cheaper and
heavier until eventually they more practical to adapt to hurricanes by, for
fall as precipitation. instance, building stronger houses.

1 Iron added Ocean fertilisation The risks of
geoengineering
Iron sulphate is added to Marine plant life is at the core of the ocean
the equatorial Pacific food chain. The plants are a source of food Geoengineering is controversial because it involves
and Southern oceans, for other marine life, and happen to take large-scale changes to Earth’s climate. Critics
which have limited iron up and bind carbon dioxide as well. They discuss possible negative side effects, like that
for marine plant growth. rely on the availability of nutrients to grow ocean fertilisation might cause toxic algal blooms, or
– most commonly nitrogen or iron. that geoengineering gives industry and government
Fertilising the oceans with iron sulphate is excuses not to cut carbon emissions.
believed to increase their growth and
reproduction, which would in turn increase Geoengineering also raises issues of ethics.
the amount of carbon dioxide they take up, Cooling the climate with sulphate aerosols “is
reducing the effect of carbon emissions. potentially cheap enough for single countries to do”,
Some scientists also believe that the says Professor Andy Ridgwell, Bristol University, but
increased marine plant life may increase could impact other countries’ climates as well.
the number of fish in the sea, in turn
improving our food supply. Others fear ‘rogue’ geoengineers. For example, an
American businessman dumped 100 tons of iron
2 Microalgae bloom sulphate into the Pacific in July 2012 in an
unauthorised ocean fertilisation scheme.
The rich iron supply creates vast blooms of tiny
marine plants, which take up CO as they grow.

2

3 Carbon locked away

As the plants die, some fall to the ocean floor,
taking locked-up carbon dioxide with them
which becomes buried as sedimentary rock.

Carbonate addition © Weather Modification, Inc/Christopher Grilliot/Bruce Boe; SPL; Peters & Zabransky; NASA

Adding powdered limestone – an alkali –
to Earth’s oceans could counteract the
acidifying effects of greenhouse gases.
Alkaline oceans also absorb more CO from

2

the atmosphere, but changing seawater
alkalinity might harm certain marine life.

carbon dioxide out of the atmosphere with any you want to use those soils to grow food. “The the two years following the eruption of Mount
of them,” explains Professor Ridgwell. “They plausibility problem is that you’re in potential Pinatubo in the Philippines in 1991, global
lend themselves to gradual mitigation.” competition with other land uses in a world temperatures cooled by about 0.5 degrees
where dietary demands are rocketing.” Celsius (0.9 degrees Fahrenheit) on average.
Growing vast new forests or fast-growing
crops competes with existing land uses, Reflecting sunlight back into space with So realistically how fast could we cool the
explains Dr Tim Lenton from Exeter University. aerosols is the fastest geoengineering method. planet? Dr Hunt concludes: “Let’s suppose the
The idea is to repeatedly harvest fast-growing It mimics the rapid cooling effect of a large Greenland ice sheet completely melts and we
crops like eucalyptus, which capture the volcanic eruption. “Once you start blocking out get a one-metre [3.2-foot] sea-level rise. It could
carbon dioxide they use to grow. Crops growing some sunlight, temperatures drop quite be done in five years – if we’ve got time to think
on the best soils take up the most carbon, but quickly,” explains Andy Parker. For example, in about it, 20-30 years from now.”

141

THE WEATHER & US

Wind tunnels

Allowing engineers to test Testing in the supersonic wind
aircraft designs in the lab, tunnel at NASA’s Lewis Flight
wind tunnels are invaluable Propulsion Laboratory
to scientific research
Both photographs © NASA
A wind tunnel simulates
in a laboratory the flow of Closed loop
air around, for example,
an aeroplane or a building. This Most – but not all – wind tunnels save
allows designers to work out the energy by feeding the moving air from
impact this airflow will have on
the finished product and make the exhaust back to the input.
cars and planes more
aerodynamic and structures more Test object Fans
wind resistant.
Wind tunnels are large circular As some drag from walls is Most wind tunnels use fans or
tubes through which air is blown inevitable, the object is mounted in banks of fans, although the very
in one direction by giant fans: the the centre of a wind tunnel where fastest use explosive expansion
test object – usually a scale model air stream is most stable.
of the actual design – is mounted of compressed air.
in the centre. In the case of an
aircraft or a plane, in reality Lighting
the object will be moving while
the air stays still, but this doesn’t Illumination is usually provided by shining
matter as long as the relative light in through windows – lighting would heat
velocity between the air and the
object is the same. An enclosed up air and produce turbulence.
cylinder is needed to allow for
uniform airflow in one direction Observation windows
(known as laminar flow),
simulating the airflow past a plane Kept level with the inside of wind tunnel and usually
moving in a straight line or the curved to keep inside as smooth as possible and
wind hitting a skyscraper. prevent introduction of turbulence.

Anatomy of a
wind tunnel

The role of each
section explained

Internal casing

Kept as smooth as possible
to minimise friction between
the wind tunnel and air,
which would introduce
turbulence to airflow.

Settling chamber

Air produced by fans is highly turbulent. Metal
grating with a series of holes filters air current
to create stable, unidirectional flow.

142

HEAD CUP 1. Mechanical PLATE 2. Pressure ULTRASOUND 3. Sonic

2HEAD Facts: These mechanically based Facts: The earliest kinds of Facts: Ultrasound anemometers
anemometers are not the most anemometers, they work by work through transmitting sonic
TYPES OF precise and accurate way of measuring the pressure wind can pulses between two receivers. The
ANEMOMETER measuring wind speeds, but they place on a set area, which in turn delay in receiving these pulses can
are the most commonly used due depresses a spring. However, they be analysed in order to gauge wind
to their simplicity and ease of use. only work for high strength winds. resistance, therefore speed.

Measuring 2. Spindle
wind speed
As the spindle turns it
drives a small electric

generator located
beneath it.

Anemometers can often be spotted in Wind speed is measured in
weather stations, but how do they knots and wind barbs show
actually give information to the direction and speed of
meteorologists about wind speed? winds on weather maps.
They point in the direction
There are several types of the wire, wind speed can be detailed. the wind is coming from.
anemometer employed to gauge Although these are delicate, they are
wind speed, but the one we extremely good when trying to analyse Calm (0-2 kn) 3-7 kn
would most probably recognise is the cup wind fluctuations.
anemometer. These have three cups 8-12 kn 13-17 kn
spaced equal distances apart on arms 1. Revolving
horizontal to a central shaft. The cups cups 18-22 kn 23-27 kn
catch the air as it drives past them,
causing the shaft to spin. By counting the The cups are driven by 28-32 kn 33-37 kn
number of turns occurring in a second, the wind and turn the
you can then calculate the average wind spindle to which they 3. Generator 38-42 kn 43-47 kn
speed. Some cup anemometers also have are attached.
tiny electricity generators built into them The generator 48-52 kn 53-57 kn
that calculate wind speed by analysing 4. Electric produces an output
how much energy the spinning meter
anemometer is creating instead of that operates an
counting the spins. The electric meter is electric meter.
There are also many other types of calibrated in wind
anemometers, which work using lasers, speed. Devices like 58-62 kn 63-67 kn
ultrasound measurements, pressure these range from five
sensors or temperature sensors. Hot-wire to 100 knots. 98-102 kn 103-107 kn
anemometers, for example, work through
the heating of a fine wire to a set level
above ambient atmosphere temperature,
and then by the precise recording of the
speed of cooling caused by wind passing

Sunblock

How does sunblock protect your skin?

The largest organ of the body, sunburn, but also from the UVA rays
your skin is an amazingly that penetrate into the skin and damage
durable and sophisticated cells, causing ageing and leading to a
substance, and yet it remains higher risk of skin cancer.
vulnerable to the Sun’s ultraviolet rays.
Apart from covering up with clothing, Sunscreens can work in two ways and
the next best way to protect this contain either organic chemical
precious layer is to wear sunscreen. The compounds, physical ingredients, or a
Sun undoubtedly has its benefits: for combination of the two. While chemical
example, exposing skin to sunlight sunscreens absorb the UV light that
enables the body to produce vitamin D, tries to pass through them, physical
which is essential to healthy bones. sunscreens act like a natural mirror that
However, you still need protection, not reflects the rays away from the skin,
only from the UVB rays that cause making it safer for you to enjoy the
sunshine, just don’t forget to reapply!

143

THE WEATHER & US Cold front
conditions
Weather forecasting
As the warm air is forced
Looks like high pressure upwards so quickly, when it
has moved in… cools and condenses it forms
cumulonimbus clouds and

therefore heavy rain or
thunderstorms. Cumulus clouds

follow on from this, with
showery conditions and

eventually clear skies.

Predicting Cold front

Heavy, cool air comes from the east behind a
body of warm air, which is forces sharply
upwards. The quick movement of air causes
cool, windy conditions.

the weather
To take an umbrella or not?
How we get those all-important forecasts…

The simple fact of the matter is that pressure (a depression), which is associated with meteorologists require vast quantities of weather
weather is unpredictable. So how is it unsettled conditions like wind and rain. data – including temperature, precipitation, cloud
that we can gather information and coverage, wind speed and wind direction – collected
make predictions about what conditions on Earth We know how a frontal weather system will from weather stations located all over the world.
will be like? behave and which conditions it will produce down Readings are taken constantly and fed via computer
Most weather phenomena occur as a result of on the ground. The man who first brought the idea of to a central location.
the movement of warm and cold air masses. The frontal weather systems to the fore in the early 20th
border between these bodies of air are known as Century was a Norwegian meteorologist called Technology is essential to both gathering and
‘fronts’, and it’s here that the most exciting weather, Vilhelm Bjerknes. Through his constant observation processing the statistical data about the conditions
including precipitation and wind, occurs. of the weather conditions at frontal boundaries, he down on Earth and in the upper atmosphere. The
As a body of air passes across different types of discovered that numerical calculations could be massive computational power inside a
terrain – such as over the oceans, low-lying areas or used to predict the weather. This model of weather supercomputer, for example, is capable of predicting
even mountainous regions – air temperature and prediction is still used today. the path and actions of hurricanes and issuing
moisture levels can change dramatically. When two life-saving warnings. After taking the information
air masses at different temperatures meet, the less Since the introduction of frontal system weather collected by various monitors and sensors, a
dense, warmer of the two masses rises up and over forecasting, the technology to crunch the numbers supercomputer can complete billions of calculations
the colder. Rising warm air creates an area of low involved has advanced immeasurably, enabling far per second to produce imagery that can reveal how
more detailed analysis and prediction. In order to the hurricane is expected to develop.
forecast the weather with the greatest accuracy,

144

HEAD FREAKY 1. Moonbows FREAKIER 2. Sundogs FREAKIEST 3. Raining
animals
2HEAD These are rainbows A phenomenon whereby there
caused by moonlight. appears to be more than one sun It has been known to
FREAKY They often appear white in the sky. Sundogs are faint ‘rain’ frogs and fish. It is
WEATHER to the naked eye, and rings of light created when thought that the animals
appear best with a horizontal ice crystals in the are picked up during
full moon. atmosphere align to refract light. tornadoes over water.

DID YOU KNOW? The MET office has more than 200 automatic weather stations in the UK; they are usually 40km (25m) apart

Warm and In practice Warm front conditions
cold fronts
The red curves of a warm front As the warm air slowly rises, it cools and
What do these terms mean and blue triangles of a cold front condenses and clouds are formed. These
and how do they affect us? are shown on a map to show are nimbostratus, causing steady rainfall,
where the fronts are, where then altostratus accompanied by drizzle,
they’re heading and the weather and finally cirrus, when clearer skies can
they’ll bring. be seen.

Warm front

This is where warm air from the
south meets cold air from the north,
and the warm air rises gradually
above the cold air.

© DKImages Stormy
weather
WEATHER FORECAST MAP Learn what these weather-related
signs and symbols mean Hail

High pressure Wind Low pressure The tops of storm clouds
are full of tiny ice crystals
Weather here will be clear and dry, due to the The conditions at this point will be windy. At the centre of these that grow heavier until
high pressure. If this high pressure occurs in This is indicated by the position of the circular patterns of they fall through the
summer weather will be warm, whereas in isobars; the closer together they are the isobars is where cloud. The biggest hail
winter it will be cold and crisp. windier the conditions. stone on record was
systems of high or low 17.8cm (7in).
pressure lie. Where
Lightning
there is low pressure
conditions will be rainy A flash of lightning is a
giant spark caused when
and windy. the molecules in a
thunder cloud collide and
Isobars © DK Images Occluded build up static electricity.
front The flash occurs when a
These indicate spark jumps through a
atmospheric pressure. This is where one cloud, or from the cloud to
Areas of equal front ‘catches up’ the ground, or from one
atmospheric pressure are with another. In this cloud to another.
joined together with the example, the cold has
lines shown and the caught up with the Thunder
numbers indicate warm. Occluded
pressure measured in fronts cause the This is the noise produced
millibars. Lower numbers weather to change by lightning. An increase
indicate low pressure, quite quickly and, in in pressure and
while higher numbers this case, become temperature cause the air
indicate similar to that of a nearby to rapidly expand,
high pressure. which produces the
cold front. characteristic sound of a
sonic boom.
Cold front In between Warm front
Storm cloud
As with any cold front, the weather here will After the passing of the warm front and The warm front will cause steady rainfall,
be expected to be cool with heavy rainfall and before the arrival of the cold front followed by drizzle, accompanied by cloudy Your typical run-of-the-
possibly even thunderstorms. This will be skies. These are typical conditions caused by mill cloud can be
followed by showers. conditions should be clear and dry, but hundreds of metres high.
normally only for a short period. any warm front. A storm cloud, however,
can reach heights of over
ten kilometres (that’s
six miles).

How many…?

16 million thunderstorms
occur each year globally.

145

THE WEATHER & US

Michael Fish

Michael FishOntheMetOffice,predictingthe
weather and that 1987 forecast

As the jokes go, whenever rain is wanted. I know these days, of course, I would Do you think it will make individuals like
forecast, there will be sunshine and imagine it’s much more difficult as the Met yourself irrelevant?
whenever sun is forecast, it will rain. Office is hardly recruiting these days. There will always be a human to interpret the
But there is no instance more memorable than information. Unless you can teach the computer
when Michael Fish MBE assured the nation that I just had an interest in that sort of thing; you to speak, then I suppose you won’t need a
the Great Storm wasn’t coming. On 15 October have interests, and my interest was weather. I weatherman on the radio. But no, a human
1987, Fish denied plausibility of a report of an wanted to be a weather forecaster. There was being has to keep an eye on the input and
incoming storm. Then the storm hit. nothing about radio or television that attracted output because computers don’t think for
We spoke to Fish about his love of the weather me, so the goal was purely to be a weather themselves. It can blindly take in duff
and his aspirations to experience being at the forecaster or possibly even doing some research information and calculate the mathematics
centre of a hurricane. into atmospheric sciences. completely wrong. Otherwise you can leave the
computer to do the job better than you could.
You started your education at Eastbourne What technology or science did you use to
College. What did you do there that led you predict the weather? Naturally I have to ask about the Great
towards meteorology? Well, when I first joined the Met Office there Storm of 1987, could you take me through
Lots of people ask me that and I’m never really was no such thing as technology really. Your your day?
sure about the answer, but I think it was tools were a pencil and rubber. In the early I can’t really remember most of it. I wasn’t even
triggered by the horrendous floods of 1953. Sixties the Met Office got its first computer and on duty. Bill Giles was the forecaster on duty the
Along the east coast and in Holland nearly 2,000 produced its first numerical forecast. We also afternoon and evening before, and he gave a
people drowned. Although I have a feeling I got the first weather satellites, which was a very low-key forecast about it being breezy up
would have developed an interest anyway, that giant leap forward. But even so, the basic the channel. The previous day I had said,
was such a major weather event that I think it forecast was done by human beings with a “Batten down the hatches, there is some
was the trigger. pencil and rubber. It wasn’t possible to do extremely stormy weather on the way.”
forecasts for more than a day or two ahead due
How did you get in to the Met Office? to the lack of facilities and computing power. As far back as the previous Sunday, the
I was determined to join the Met Office so I went And now, with the world’s biggest computer, it’s computer had predicted that there would be
on to get the right qualifications. I studied and possible to forecast for ten or fifteen days with horrendous gales at the end of the week. But as
passed Maths, Physics and Chemistry at A-level no problem whatsoever. It is predicted that it got nearer and nearer to the event, the
then went straight into the Met Office within a they’ll be able to produce really accurate computer slowly changed the track of this
few weeks of leaving school. And in those days forecasts that pinpoint things to a few hundred particular deep area of low-pressure. So where
it was quite easy to step into the career you metres and look weeks and maybe months on the Sunday it had forecast the storm to hit
ahead. No human being could ever do that. south-east of England – which is where it did hit
– by the Friday morning, when I was on duty, it
said it was going to cross northern France and
we were only going to experience strong winds.
Hence why Bill Giles said it was going to be
breezy up the channel.

But, of course, Sod’s Law decreed and at the
very last moment it changed course and caused
the devastation we saw. It’s unfortunate that
the computer didn’t get all the information it
would usually get to do its sums.

The Great Storm aside, what would you say
was your most life-altering experience of
extreme weather?
I think it was during my first month at the Met
Office, when I was working at Gatwick Airport.
London had its last great smog and all flights to
Heathrow were diverted to Gatwick. There was
absolute chaos because the planes couldn’t be
parked anywhere. Shortly after that, at the end

146

of 1962 to the beginning of 1963, we got the most “The problem is even if we do © Verri Media Production Ltd; Channel 4
severe winter that the country’s seen for over something about it now, it’s
100 years. Everything in the house froze up, I probably too late”
froze up and all the rest of it. It was quite a
dramatic welcome to the Met Office, with some
of the most severe weather for hundreds of
years being forecast.

If there was one extreme weather event you
would like to experience in your life, what
would it be and why?
I want to experience a hurricane. I want to go on
one of the American Weather Bureau flights
that run into the centre of a hurricane in order
to take measurements of the wind, the
pressures and so on. Or if that was not possible,
I would get myself in a safe place and
experience a hurricane on the ground. I’ve done
storm chasing on a couple of occasions, so I
have seen and experienced tornadoes, but I’ve
never seen or experienced a hurricane. Or a
typhoon. I’ll go to Japan as well as America.

In the future, do you think we’ll
experience another Ice Age or feel the
effects of global warming?
We’re certainly not going to have another Ice
Age for the very reason that global warming is
having an effect. I give lectures on global
warming which I title ‘The Ultimate Weapon of
Mass Destruction’ because there is no doubt
that millions of people have already died as a
result of global warming.

Billions of dollars of damage has been done
– not least to the British Isles early this year –
and it’s only going to get worse. It will be more
severe everywhere. There are going to be more
hurricanes, more floods, more typhoons, more
devastation. The average temperature of the
world will continue to rise and it could get to
quite dramatic levels by the end of the century
if nothing is done about it. The problem is even
if we do something about it now, it’s probably
too late.

Do you think there is anything we can do
about global warming?
We can slow it, but we can’t stop it. What we
have done already is going to continue for the
next hundred years or more. But we can slow
global warming and hopefully make it more
manageable. But it is going to have to be done
quickly to make a difference.

Catch Fish on www.netweather.tv every
Thursday giving a video forecast and lectures
on the impact of global warming.

147

THE WEATHER & US

Renewable/Non-renewable energy

Renewable vs
non-renewable energy

What will we do when all the fossil fuels run out?

We have already discovered such as cost and efficiency mean we are Sources of energy
lots of new sustainable sources still relying on coal, oil and gas a great
of energy in our mission to deal. As with most forms of technology, The pros and cons of all our available energy options
replace fossil fuels, and it’s likely we will it’s likely that cost will decrease and
discover several more as science and efficiency will increase over the course Biomass Nuclear power plant
technology progresses. of time, but what else is stopping us from
However, renewable sources switching to solar, wind and all the (renewable) (non-renewable)
currently only supply about ten to 20 per other renewable sources that are
cent of our energy needs, as obstacles available to us? PRO: Can provide PRO: Raw materials are
electricity and fuel efficient and inexpensive

PRO: Cheap and abundant PRO: Does not give off
source of energy greenhouse gases

CON: Gives off CO CON: Nuclear waste is highly
2 toxic
when burned
CON: Nuclear reactors are
CON: Only renewable if expensive to run
crops are replanted

Wind farm
(renewable)

PRO: Can power single
households as well
as entire towns

PRO: Gives off no
greenhouse gases

CON: Noisy and expensive
to set up

CON: Reliant on wind

Tidal
(renewable)

PRO: Predictable and
reliable energy source

PRO: Gives off no
greenhouse gases

CON: Expensive to set up
CON: Can have negative

effects on the
environment

148

Solar Hydroelectric

(renewable) (renewable)

PRO: Solar panels are quiet PRO: Creates water reserves
and low maintenance as well as energy

PRO: Gives off no PRO: Gives off no
greenhouse gases greenhouse gases

CON: Panels are expensive CON: Can cause flooding of
to manufacture local areas

CON: Reliant on sunlight CON: Expensive to set up

Coal Geothermal

(non-renewable) (renewable)

PRO: Cheap to mine PRO: No harmful gases
PRO: Abundant supplies are produced

worldwide PRO: Abundant energy
CON: Gives off CO supply

2 CON: Expensive to
set up
when burned
CON: Destruction of land CON: Reliant on
volcanic activity

Oil Gas Timber © Sol90

(non-renewable) (non-renewable) (renewable)

PRO: Easy to extract and PRO: Cleaner than oil PRO: Cheap and abundant
distribute or coal source of energy

PRO: Powerful and PRO: Easily transported PRO: Sustainable, long
versatile fuel CON: Gives off CO term source

CON: Gives off CO 2 CON: Gives off CO
2 2
when burned when burned when burned
CON: Dangerous to
CON: Difficult and costly CON: Only renewable if
to find new sources work with trees are replanted

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THE WEATHER & US

Solar power

© Science Photo Library

Charge your gadgets, heat your home and even
get paid for generating your own electricity

Renewable forms of power generation Sun works by emitting solar radiation that is electricity (voltage) is achieved within the
are essential. As the fossil fuels we equivalent of 1,367 watts of power per square metre. photovoltaic cell. When sunlight hits the cell,
currently rely on begin to run out, we This is known as the ‘solar constant’. which is usually made out of silicon, it makes
need to find a replacement for the world’s energy electrons come loose from the atoms they are
needs. The impact that burning oil and gas has The Sun is a massive fusion reactor, pumping out attached to. This action produces electricity. The
on the environment must also be addressed if its energy (3.8 x 1026 joules per second) in all more sunlight that hits the cells the more electricity
we are to stop and reverse the effects of global directions. On the Earth we only feel a fraction of is produced, which you can then use to heat your
warming. One of the main forms of renewable this energy. The Sun actually delivers about 7,000 water or charge your phone.
energy that has now entered the mainstream is times more energy to the Earth’s surface than we
solar power. globally generate and use at the moment. The Across the world, every country is looking closely
Capturing even a fraction of the Sun’s energy that tricky part is capturing that incredible energy and at how they can use more renewable energy sources.
hits the surface of the Earth could mean we are able using it efficiently. Not surprisingly, solar power is most popular in
to close our gas and coal-fired power stations. The countries lucky enough to get sustained periods of
Solar cells are properly known as photovoltaics, sunshine. Spain and Portugal currently lead the way
as the process of converting light (photo) into

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