Indholdsfortegnelse for Understanding Meteorology i Understanding Meteorology

The weather affects us all. Whether it’s something as small as deciding if we should wear a sun hat or raincoat, or as big as preparing for an incoming tornado or battling the effects of climate change, it’s important to understand how and why these things happen. What are sunrays made from? Why are rain clouds grey? How do snowflakes form? Can we control storms? What will happen if we don’t reduce the impacts of climate change? In this brand-new special edition, we’ve compiled a selection of articles from How It Works to explain the science behind these questions and answer everything you ever wanted to know about meteorology. Disclaimer: The information in this book was correct at the time of original publication, but may have changed since.…

The weather affects us all, every day. From governing the difference between life and death, to providing a conversation topic to fill awkward silences at a party, it is an ever-present and ever-changing part of life. This means that predicting it accurately is a hugely important task. In the UK, the Met Office is responsible for weather monitoring and prediction. Before a forecast can be put together, measurements from thousands of data recorders across the world are collected and analysed. Every day, around 500,000 observations are received, including atmospheric measurements from land and sea, satellites, weather balloons and aircraft. But, this is still not enough to represent the weather in every location. To fill in the gaps, the data is assimilated. This combines current data with what is expected, to…

The water – or hydrological – cycle is the Earth’s water recycling system. Since water rarely escapes the planet or arrives from space, the water cycle keeps rivers relentlessly flowing into the oceans and the atmosphere supplied with clouds and rain. Without it, life simply couldn’t exist. The water cycle circulates water between the oceans and atmosphere, sometimes via the land. When ocean water is heated, it turns into water vapour, which rises into the atmosphere and is carried by winds. The vapour cools at some point and forms clouds. Around 78 per cent of the rain, snow and other forms of precipitation falling from these clouds goes straight back into the ocean. The rest falls over the Earth’s continents and islands. Some of this water runs into rivers and…

The air around you contains water in the form of a gas called water vapour, and the amount of vapour it contains is known as its humidity. If you have ever visited somewhere with a tropical climate then you may have experienced humid, muggy air, which can often leave you feeling uncomfortably hot. This is because the air around you is saturated, and cannot hold any more water vapour, so the sweat from your skin cannot evaporate to cool you down. Humidity can actually also affect you in cool climates, as the water vapour in the air conducts the cold temperature onto your skin, making you feel colder. “The air is saturated, and can’t hold any more water vapour” Calculating humidity How does air temperature affect the relative humidity? 1…

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’s due to a slight change in the 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…

To understand why clouds can appear grey, you first need to know why they also appear white. It’s all to do with the reflection of light. Clouds are formed when air and water vapour near the ground warms up and rises. As it gets higher, the water vapour condenses, and the droplets join together to form clouds. The more condensation there is, the more droplets there are and the bigger the clouds become. When light from the Sun passes through these large accumulations of water vapour, the droplets scatter the light in all directions. The droplets are small and spread out enough to scatter the entire spectrum of light, which means that they will appear white. As more water droplets gather and the clouds grow larger, less light is able…

Cloud seeding is a clever way of manipulating the weather to alter how much rain falls. It was first discovered one hot July in New York, 1946. Dr Vincent Schaefer was experimenting with creating clouds and placed a lump of dry ice inside a chamber to cool it down. He noticed that the water vapour in the chamber formed a cloud around the dry ice. This replicates one of the ways that clouds form naturally – as air cools, water vapour clings to tiny particles floating in the air, such as salt and dust, called aerosols. This is known as condensation. As more water vapour sticks to the aerosols, the drops get larger and start sticking to other droplets, forming clouds. Then, as the droplets grow, they become raindrops. It’s…

Have you ever seen a swirling tornado of fire, or heard a sand dune sing? Perhaps you’ve witnessed balls of lightning floating in the sky or even been caught in a downpour of frogs. Even if you haven’t, someone elsewhere in the world definitely has. Although most of the weather we encounter on a day-to-day basis isn’t particularly exciting, it can occasionally deliver some incredibly strange surprises. From enormous hailstones the size of tennis balls to towering clouds of dust that engulf entire cities, weather has the potential to be breathtaking, destructive and even explosive. The basis for most weather is wind, water and temperature. Thunderstorms are the perfect example, as they involve all three at once. As the Sun heats the Earth, moisture in the air rises up into the cooler…

A frost quake, or ice quake (scientifically known as a cryoseism) is a rare, natural phenomenon that makes the ground shake in the immediate proximity of its epicentre and produces a loud booming sound. These kinds of tremors are very similar to earthquakes, but the meteorological and geological conditions at work make them very distinct events. Frost quakes occur in areas susceptible to cold air masses. Usually there is some snow covering on the ground, but only around 15 centimetres (6 inches) – not enough to insulate the ground. For a frost quake to happen, the ground must become saturated, which could occur after heavy rain or from a thawing of ice or snow. When such a large quantity of water seeps down into the soil or bedrock, the ground inevitably…

“Anticyclones are associated with summer weather and dry winter days” Cyclones and anticyclones are generated when areas of high and low air pressure collide. These are created by differences in temperature and humidity. Air temperature affects the molecules’ kinetic energy. The higher the temperature, the more the molecules move and collide. Humidity, on the other hand, affects the air itself. The atmosphere’s main constituents – diatomic oxygen and nitrogen – are heavy compared to water vapour. The water in humid air replaces some of the heavier molecules, making it lighter than dry air, and therefore of a lower pressure. An anticyclone is a region of high atmospheric pressure. The air descends through the system, spreading out sideways as it makes contact with the ground. The compressed air causes a rise…

How noctilucent clouds form Did you know? The biggest cloud is the cumulonimbus. They’re dark and can contain millions of tons of water. What are snow doughnuts? Snow doughnuts, or rollers, are a rare natural phenomenon. If snow falls in a clump, gravity can pull it down over itself as it rolls. Normally it would collapse, but sometimes a hole forms. Wind and temperature also play key roles. Raining animals The very real threat of amphibious rain Although there are no accounts of it actually raining cats and dogs, other animals, such and fish and frogs, have been seen to fall from the sky in some parts of the world. This occurs when waterspouts – small tornadoes that form over water – suck up low-weight items, such as small creatures,…

“Within 30 minutes the El Reno tornado was moving at 80kph (50mph)” Widest tornado The classic tornado is funnel-shaped with a narrow bottom, but this isn’t always the form these storms take, as the residents of El Reno, Oklahoma, found out on 31 May, 2013. At around 6pm local time, the El Reno tornado formed at an intersection about 15 kilometres (nine miles) southwest of the city. It soon began moving towards the town and rapidly increased in speed and size. Within 30 minutes it was moving at 80 kilometres per hour (50 miles per hour) and had ballooned into a massive maelstrom of thunder and wind 4.2 kilometres (2.6 miles) across. Luckily, it largely missed the city as it tore across 16 kilometres (ten miles) of farmland, ripping up crops and…

When you think of a monsoon, you probably think of torrential rains causing flooding, but there is more to these downpours than a single storm. A monsoon is actually a reversal of wind direction. These weather events cause heavy rain in summer and dry spells in winter as the prevailing winds shift as land heats and cools. There are only specific areas of the world that are susceptible to this extreme weather, known as monsoon zones, and these are typically found in subtropical regions. Countries that suffer from regular monsoons include Bangladesh, India, Thailand and Sri Lanka, and they can experience anything from violent thunder and lightning to harsh dust storms. How a monsoon works The constant tug of war of the winds between the land and the sea…

Tsunamis form through a complex, multi-stage process that emanates from the massive energy release of a submarine earthquake, underwater or coastal landslide, or volcanic eruption. The first stage in this formation begins when the tectonic upthrust caused by the quake or impulse event causes massive amounts of ocean water to be displaced almost instantaneously. This action kick-starts a simple series of progressive and oscillatory waves that travel out from the event’s epicentre in ever-widening circles throughout the deep ocean. Due to severe levels of energy propagated from the impulse, the waves build in speed very quickly, reaching up to an incredible 805 kilometres per hour (500 miles per hour). However, due to the depth of water, the speed of the waves is not visible as they expand to have incredibly…

On a stormy day, if you can see a towering rod of clouds topped with a funnel-shaped horizontal cloud, there’s a chance you are looking at a supercell. What separates supercells from regular thunderstorms is the rotating movement of air at the centre as it’s drawn upwards to the top of the storm. Supercells are the least common form of thunderstorm. To spot a supercell in the distance, you need to observe the shape and movement of the clouds decorating them. The most important factor that causes a supercell to form is wind shear. Wind shear is conflicting wind direction and speed that stops the air travelling smoothly straight across Earth’s surface. The force of wind shear manipulates this movement into a rotating cycle. The strong winds, giant hailstones and…

There’s no doubt that our climate is changing – NASA says the evidence is unequivocal. Current warming is happening faster than at any other time in the past 10,000 years. But the effect a warmer world will have on hurricanes is hard to predict. Rising global temperatures are likely to impact hurricanes because tropical cyclones feed on warm, wet air. But the complex nature of these storms makes it impossible to know exactly how they’ll change over time. On average, the evidence suggests that hurricanes are likely to become more frequent and more dangerous. As the world gets warmer, the air will get wetter, and wetter air means heavier rain. It’s chemistry: the hotter it is, the more evaporation there will be. Storm-induced flooding will also be more likely as…

In January 1996, 100 million tons of snow fell on the streets of New York City and nearby Philadelphia was buried under a record 78 centimetres (30.7 inches). Ice storms and sub-zero temperatures stretched as far south as sunny Florida, trapping people in their homes, often without electricity. In 1891, easterly winds dumped 3.6 metres (11 feet) of snow in London. Trains were completely buried under tremendous drifts and 65 ships sank under the heavy ice and snow. Blizzards form exactly like thunderstorms. A cold front pushes warmer, moist air into the atmosphere, condensing into clouds. If temperatures stay below freezing, snow falls instead of rain. If huge amounts of snow are accompanied by gale-force winds, it’s possible to achieve a complete whiteout, when earth and sky merge in a…

Geoengineering projects are all created to change Earth’s climate, but they’re not all designed to function on our planet. Space geoengineering involves taking a large step back from Earth in an attempt to make more significant alterations. Entering space means being closer to the Sun, and so much of the geoengineering technology envisaged for Earth orbit involves manipulating the sunlight that illuminates and warms our planet. The first idea for this type of space-based technology came from engineer James Early in 1989. His concept involved building a giant glass sheet, around 2,012 kilometres (1,250 miles) in width. When orbiting Earth, this glass structure would serve as a barrier between the Sun and Earth, reflecting sunlight back into space and reducing the radiation that entered Earth’s atmosphere. This substantial solid structure…

Our atmosphere (made up of 78 per cent nitrogen and 21 per cent oxygen, with other gases making up the last per cent) is held in place by gravity and consists of a number of different layers that work together to protect us from solar radiation and to keep consistent temperatures. The atmosphere gets thinner with altitude, with 80 per cent of its mass in the first layer closest to the Earth’s surface. There are five main layers that make up the atmosphere. The troposphere is the first layer (and is where our weather occurs), followed by the stratosphere, mesosphere, thermosphere and exosphere. There is no definite boundary between where the atmosphere ends and outer space begins, though the Kàrmàn line at 100 kilometres (62 miles) above sea level is…

If you’ve ever looked out at a sunset and seen those intense beams of light radiating from what looks like the Sun sinking behind a cloud, then you’ve seen crepuscular rays. These rays only form when it’s partially cloudy, and they are at their best when the clouds are quite thick and low in the atmosphere, such as cumulus or stratocumulus clouds. As the light from the Sun falls on the clouds, gaps in the clouds let the light through. Dust particles and water vapour in the air cause the light to scatter, much like how the beam of a torch appears if you shine it through smoke. This is what makes the rays so obvious to the human eye. The shadows cast by the clouds themselves enhance this effect.…

Rain is defined as liquid precipitation. It is formed high above the ground in clouds by water vapour coming together into large droplets that become too heavy for the air to support. Gatherings of condensed water vapour are called clouds, and this is where rain comes from. Although a large amount of water is held in each cloud, rain does not fall all at once from the cloud because the water droplets grow at different speeds, with the fastest growing droplets becoming heavier quicker and falling first, the slower growing ones falling after. Although scientists are not sure if there is water on other planets, the phenomenon of rain has occasionally been recorded. This rain involves other liquids, such as methane which falls on Titan, Saturn’s moon, and sulphuric acid…

Lenticulars are slow-moving, lens-shaped clouds that form at high altitudes of over 1,980 metres (6,500 feet) above sea level. Their most intriguing feature is that they look a lot like classic B-movie UFOs and are frequently mistaken for extra-terrestrial flying saucers. They are formed when fast-moving air rises and is forced over a topographic barrier, such as a mountain. This interruption in airflow forms a trough in the middle of the cloud, creating their distinctive shape. These clouds are ideal for adrenaline junkies in hang gliders or sailplanes. Due to their high winds, they help push the aircraft along and create a fast-moving chamber of air for the glider. However, the clouds are a no-go area for aircraft with an engine, as these fast moving wind currents can cause huge…

Most of the time, clouds hover far above our heads at high altitude. In these colder conditions, the air loses the ability to hold onto water vapour and releases droplets of liquid water. Although it forms in a similar method to clouds, fog extends into lower altitudes and can lie just above the ground. Fog forms when the air’s water vapour content is high and conditions are humid. Being close to the ground, the water-filled air reduces visibility and limits the navigation of cars, ships and aircraft. The extent of fog disruption depends on the concentration of water droplets in the air, with the thickest fog usually arising under contrasting conditions, where cold air meets warm air. The foggiest place on the planet is an area of the Atlantic Ocean…

Lightning occurs when a region of cloud attains an excess electrical charge, either positive or negative, that is powerful enough to break down the resistance of the surrounding air. This process is typically initiated by a preliminary breakdown within the cloud between its high top region of positive charge, large central region of negative charge and its smaller lower region of positive charge. The different charges in the cloud are caused when water droplets are supercooled within it to freezing temperatures and then collide with ice crystals. This process causes a slight positive charge to be transferred to the smaller ice crystal particles and a negative one to the larger ice-water mixture, with the former rising to the top on updrafts and the latter falling to the bottom under the…

“Strong winds can be life-threatening, but wind also benefits the planet” 1 Polar easterlies These dry winds move from cold, high-pressure areas at the North and South pole to low-pressure areas. They blow from the east. 2 Polar front The region between tropical air and polar air is called the polar front. 3 Westerlies In the middle latitudes – between 30 and 60 degrees – westerlies are the prevailing winds from the west. They often produce anticyclones. 4 Hadley cells These cells make up the global tropical atmospheric circulation. Air rises near the equator and moves towards the poles. 5 Trade winds These easterly winds blow around Earth near the equator. Trade winds produce ocean currents, used by early sailing ships and modern commercial ships for quicker journeys. 6 Mid-latitude…

There’s always one thing that can brighten up a drizzly day, and that’s a rainbow. Arching across the sky, these spectacles of light are formed when moisture in the air interrupts the path of sunlight, splitting it up into all the colours of the spectrum. You might be surprised to discover that raindrops aren’t their assumed ‘teardrop’ shape, but are spherical, an important distinction when it comes to making rainbows. A raindrop’s spherical shape and increased density compared to air provide the conditions needed to bend light to the perfect rainbow-making degree. When sunlight passes through a raindrop, the direction the light is travelling is changed, known as refraction. The light is refracted as it enters the droplet, then internally reflected and sent back out the raindrop in the opposite…

Freezing rain usually begins as snow, ice, sleet or hail. When it passes through a layer of warmer air, it melts and turns back into a liquid. However, if the rain travels through a shallow layer of cold air – with a temperature below freezing – as it continues to fall, this supercools the water droplets. When these droplets hit an object, such as a road, vehicle or tree, they freeze on impact. This can create dangerous driving conditions, and the weight of ice on power lines or trees can cause them to collapse. While freezing rain is more common in the US, it is a rare occurrence in the UK, as conditions have to be so precise. The sub-freezing layer must be relatively shallow, at 600 metres (1,969 feet)…

It’s a weather phenomenon that has puzzled the minds of scientists for thousands of years. As far back as the ancient Greeks, there have been eyewitness accounts of floating, glowing balls of electricity emerging after a thunderstorm. These balls of energy have ranged from the size of a golf ball to a few metres/feet wide. There have even been reports of the plasma-like balls floating in the sky and entering people’s homes before vanishing. Explanations for these electrical oddities vary, but one of the only theories to be proven in a laboratory is the theory of vaporised silicon. In the ground, soil and sand have high quantities of silicon dioxide. When this compound is heated by the energy emitted by lightning it creates balls of light, which could explain ball…

Top tempests The super storms that left behind a trail of destruction Biggest ever typhoon Super Typhoon Tip developed out of a tropical storm over the western Pacific Ocean in early October 1979. Over the next three weeks it whipped up the sea and land between Micronesia and Japan with wind speeds that reached 306kph (190mph) over a diameter that stretched to 2,220km (1,379mi). Strongest cyclone Typhoon Tip is the most intense tropical cyclone on record. It holds the record for the lowest central pressure at just 870 millibars at sea level, as well as the highest sustained winds (10-minute average winds of 306kph/190mph). Longest-lasting tropical storm In 2024, Cyclone Freddy gained the world record for the longest-lasting tropical cyclone. It formed in February 2023 and travelled for more than…

Acid rain is the broad term used to describe precipitation that is more acidic than normal. Typically, rainfall has a pH of 5.6 – anything below that level is considered acid rain. Of course, clouds aren’t in control of the pH of their precipitation – just like the rest of the natural world, it’s impacted by pollution emitted by cars and industry. The two main gas pollutants responsible for acid rain are sulphur dioxide (SO2), released as a byproduct of the fossil fuel industry, and nitrogen oxides (NOX) from vehicle exhausts. When these gases drift into the atmosphere, they interact with sunlight and water vapour to form sulphuric acid and nitric acid mists. Under warm temperatures, the clouds of acid mist remain as vapour. However, when temperatures cool, the vapour…

On 26 December 2004, an undersea megathrust earthquake caused a huge earth subduction and triggered a series of devastating tsunamis that ravaged almost all landmasses bordering on the Indian Ocean, killing over 230,000 people in 14 different countries. The hypocentre of the main earthquake was approximately 161 kilometres (100 miles) off the western coast of northern Sumatra and emanated from the ocean floor 30.6 kilometres (19 miles) below the area’s mean sea level. Here, a massive rupture in the ocean floor caused massive tectonic plate movement – an event felt as far away as Singapore – as well as the creation of numerous secondary faults that elevated the height and speed of generated waves to titanic levels. The fallout from the earthquake and resulting tsunami was the worst for over…

Hurricanes are some of the strongest and most dangerous weather events on the planet. Between 2000 and 2020, they claimed the lives of 2,137 people in the US alone. These rotating thunderstorms are relentless, taking days to pick a path through towns and cities before burning out. Each one can measure 483 kilometres (300 miles) from end to end and stretch 15 kilometres (9.5 miles) into the sky. And they all have winds in excess of 119 kilometres per hour (74 miles per hour) – the Labor Day hurricane of 1935 topped out at 298 kilometres per hour (185 miles per hour). The ability to predict storms has changed the world. People in hurricane-prone areas now receive warnings days before deadly winds arrive. But it’s not an exact science. One…

Climate goes far beyond weather. It explains why there are such predictably disparate regions on Earth and such wide variations in things like temperature, precipitation, humidity, wind, vegetation and plant life. There are a lot of different factors that play into the different climates present on our planet, and they work together in a complex way. One is the differences in how air circulates around the Earth. Depending on where you are located, you are in the path of a different wind belt or cell, with its own unique characteristics. They are considered the ‘weathermakers’ for the latitudes they occupy, as they both affect and are affected by temperatures on the Earth’s surface. Each of the five main lines of latitude – Arctic, Tropic of Cancer, the equator, Tropic of…

There’s a limit to how much greenhouse gases our planet can absorb without a drastic change to the climate worldwide. The point at which this can no longer be reversed is called the tipping point. For each element of climate change – from melting glaciers to declining coral reefs – there is a point of no return. One way to envisage this is to think about a child on a slide. There is a crucial point in this journey in which someone has committed to going down the slide, and they can’t go back up. This transforms their state from being at the top to being at the bottom. It’s important to learn about and act on the impact of global warming on the planet before it becomes irreversible, but…

Weather forecast centres around the world are constantly analysing atmospheric conditions on Earth. The public are then supplied with this information in the form of pictographic maps detailing precipitation, cloud, wind speed/direction, temperature, and frontal systems. Have you ever watched the weather update on the news and wondered what all the symbols on the weather map mean other than just sunny or raining? Below you’ll find a more detailed view of weather symbols. Use them to decipher the next weather map you read. Types of weather The other symbols found on a weather map include the various types of weather. The following classification symbols are based on those the Met Office uses. There are additional symbols for day and night variations… Temperature Temperature is shown as a figure (measured in…

Ozone is a pale-blue gas composed of three bonded oxygen atoms. It occurs naturally high up in Earth’s atmosphere, where it protects the surface from harmful ultraviolet rays – unless dissipated by natural or human phenomena. It’s also considered a pollutant, with adverse effects for humans and other creatures when present closer to the ground. Ozone is a relatively unstable substance and can be destroyed by molecules containing nitrogen, hydrogen, chlorine or bromine, which rip ozone’s third oxygen atom away from its two partners. Starting in the 1950s, scientists began measuring ozone concentrations above Antarctica, giving them the first hints that there was a problem with the ozone layer. By the 1980s, researchers were able to map a yearly hole that opened in the ozone layer over Antarctica in the…

Everyone loves a blue sky, but why does it take on that colour when it isn’t obscured by clouds? The answer lies in the physics of what happens when sunlight passes through the atmosphere. The light rays are scattered in all directions as they hit air molecules, and light at the blue end of the spectrum is scattered more strongly than other colours. That’s why the sky usually appears blue when we look in any direction away from the Sun itself. Above Earth’s atmosphere, in space the sky looks black even in sunlight. That’s one of the most striking phenomena experienced by travellers on Blue Origin’s suborbital flights: “To see the blue colour whip by you, and now you’re staring into blackness,” as William Shatner put it after his flight.…

Despite being seen as an unwelcome form of weather by many, rain is an essential event for sustaining life on Earth. Communities throughout history have always welcomed rainfall as an aid to their growing crops – and scientists think it’s for this reason that so many still enjoy the smell that follows the rain. This is called petrichor. The raindrops themselves aren’t responsible for the scent that fills the air after it starts to rain. Rather, the water droplets cause various fragrant compounds to be released from the soil. As raindrops scatter over dry earth, the water traps tiny bubbles of air at the ground’s surface. These droplets then splatter, bursting the bubbles from the loose soil and carrying plant oils and other natural chemicals upwards into the air in…

This type of cloud was officially recognised by the UN’s World Meteorological Organization in 2017. After being unable to identify the clouds from photos sent in by sky watchers all over the world, the Cloud Appreciation Society proposed that they should be officially classified as Undulatus asperatus, inspired by the Latin word for ‘roughened’ as they look like choppy seas in the sky. Although their formation is not yet entirely understood, some experts believe that they form under the same conditions as mammatus clouds, which look as though they have a series of pouches hanging below them. These occur when ice crystals in the clouds sink, but are too large to evaporate in the air below. To form an asperitas cloud, strong winds then shear the underside of the mammatus…

Air in the atmosphere is constantly on the move. Composed of several layers – from just above ground level to high in the sky – air particles are subjected to varying pressures and energy distribution. Whether in slight movements to carry heat from the equator towards the poles or through strong currents called jet streams, air is on a continuous journey often impossible to see. Earth’s atmosphere is divided into five main layers, with the troposphere lying closest to the surface. Ranging from six to 20 kilometres (3.7 to 12.4 miles) in thickness, the troposphere consists of two layers: the upper layer, known as the free atmosphere, and the lower layer, known as the planetary boundary layer. The bottom layer begins at the Earth’s surface and stretches up around 1,000…

Regular rainbows occur when moisture in the air – commonly rain, but also mist or spray from a waterfall – refracts sunlight in such a way that it is broken up into its constituent colours. The phenomenon occurs when the Sun is positioned behind you and sunlight passes through the airborne water. The light refracts (bends) inside the droplets and the white light is broken up. Each colour has a different wavelength so, depending on the angle of refraction, a different colour of light will be reflected outwards; the result of this process is what we observe when we see a rainbow. Every rainbow is accompanied by another, secondary rainbow, but it’s usually too dim to see. This double rainbow effect is due to the continued reflection of light inside…

La Niña is defined by unusually cold ocean temperatures in the equatorial Pacific. It’s caused by a build-up of very cool water in the tropical Pacific, which is brought to the surface by easterly trade winds and ocean currents. This upsurge of water causes sea-surface temperatures in areas near South America to drop drastically. La Niña can trigger changes in rainfall patterns, atmospheric circulation and atmospheric pressure, having dramatic effects on the global climate. La Niña events are associated with cataclysmic flooding in Northern Australia. In 2010, they resulted in arguably the worst flooding in Queensland’s history, causing more than two billion Australian dollars’ worth of damage and requiring the evacuation of over 10,000 people. La Niña does have some positive effects, however, often boosting the South American fishing industry…

Lightning Collisions between water droplets and particles of ice in storm clouds create a strong electric field, which separates atoms into positively charged protons towards the top of the cloud and negatively charged electrons towards the bottom. Eventually the charge builds up so much that electrons shoot towards the protons within the cloud or towards the positively charged ground in a flash of lightning, one of Earth’s most breathtaking light displays. Bioluminescent phytoplankton Various species of phytoplankton produce light, but the most common are dinoflagellates. Movement of predators within the water likely starts a chemical reaction, which causes a protein called luciferin to produce a bright blue light. This is thought to act as a form of defence against predators. To catch this incredible light look out for calm, dark,…

For areas that rely on regular rainfall to nourish vegetation, animals and a large human population, drought can be devastating, but in other parts of the world, hot, dry weather is a normal everyday occurrence. These arid climate conditions are caused by circulatory patterns of air in the Earth’s atmosphere, known as Hadley cells. In this weather system, intense exposure to sunlight at the equator causes warm, moist air to rise. As the air rises, it cools again, forming a low-pressure system that results in regular thunderstorms across the region. Above these storms, the jet stream – a current that flows through Earth’s upper atmosphere – carries the air towards higher latitudes until it eventually descends over the tropics north and south of the equator. As it falls, it creates…

Northwest America hosts some of the strangest and most spectacular landforms on our planet. Scarred into the black rock are giant channels carved out by water – the largest is the Grand Coulee in Washington at 97 kilometres (60 miles) long. In 1922, geologist J Harlen Bretz began investigating how these channels formed. He initially attributed them to the slow action of rivers, but the more he looked into it, the more unusual landforms he discovered. Among them were piles of gravel some ten storeys high and hills shaped like boat prows. These gargantuan features were best explained by water tearing through the landscape – an unimaginably massive megaflood. The prow-shaped hills pointed in the direction of flow, while the gravel was dropped when the floodwaters receded. Bretz tracked the…

Severe storms have caused some of the world’s worst weather and inspired several highly implausible movies. Responsible for countless deaths and damage, super storms, scientists fear, could get stronger in the future due to climate change. The giant hailstones, violent winds, pounding rain and huge tornadoes that make wild weather a disaster-movie staple are mainly associated with two weather systems – the supercell thunderstorm and hurricanes. Depending on location and strength, hurricanes are also called typhoons, severe tropical cyclones or severe cyclonic storms. Hurricanes are around a hundred times bigger than supercell storms, but supercells pack vast energies into a thunderstorm less than nine kilometres (5.6 miles) across. Supercell storms can spawn violent tornadoes, which can reach wind speeds of up to 512 kilometres per hour (318 miles per hours),…

Polar/tundra Generally the tundra has one month with an average temperature of 0°C (32°F), but no months with an average high greater than 10°C (50°F). There is low rainfall and snowfall, and vegetation comprises dwarf shrubs, lichen and grasses. Examples: Alaska, northern Canada and Russia, Greenland, Iceland and northern Scandinavia. Boreal/coniferous forest Boreal/coniferous forests are usually in areas of higher elevation, between 900 metres (2,953 feet) and 1,300 metres (4,265 feet) above sea level. There is a high level of both rain and snowfall and very cold temperatures. Examples: Uplands of New England, inland Canada and Alaska, northern Norway, much of northern Asia. Mountain Mountain regions are above the tree line – the line at which trees stop growing due to extreme cold or dryness. High elevations mean colder temperatures…

1 Floating vessels The towers are constructed on a fleet of autonomous boats. 2 Sea to sky Water is pumped from the sea and sprayed into the sky through these towers. 3 Cloud composition The fine spray of seawater reduces the average droplet size within the surrounding clouds. 4 Light on white The small droplets in the clouds scatter light, making them appear white. These white clouds reflect more sunlight away from Earth. 1 Iron offload Boats release large amounts of iron into the ocean. 2 Phytoplankton Microscopic marine algae need iron to produce food and grow. Adding iron creates algal blooms. 3 Carbon dioxide absorption Phytoplankton absorb carbon dioxide from the atmosphere and release oxygen. 4 Sinking CO2 As phytoplankton die, they sink below the surface, carrying the absorbed…