The Climate Change Schools Resources were developed by the Climate Change Schools Project, based at the then Science Learning Centre in Durham and led by Krista McKinzey. A large number of teachers and schools in North East England were involved in their development.
They have subsequently been updated by the Royal Meteorological Society.
Sailing is one of the most weather-dependent sports. Unfortunately, wind is not just a useful source of power for sailing craft but also a hazard. Strong winds can capsize boats, either directly or in combination with the waves they may produce.
The wind is never steady. It always fluctuates between gusts of higher wind speed and lulls that may be so light as to be near-calm. However, sudden increases of wind on a larger scale can sometimes occur. These are called squalls and are often associated not only with strong, gusty wind but also with heavy rain.
The importance of any hazard varies with the skill level of the crew, the type of boat and the kind of sailing being undertaken. For example, a novice crew in a small boat may underestimate wind strength before setting off. This is an easy mistake to make, especially if they are launching from a relatively sheltered location. Sailors who are more experienced are unlikely to be caught out like this but are still vulnerable in other ways. Hard sailing, especially in colder conditions, can tire a crew very quickly. Exhaustion or exposure can creep up on them before they know what is happening. For example, a dinghy crew might be having great fun practising sailing across the wind, only to find when they feel they have had enough that they do not have the reserves of energy for a long struggle upwind or a tricky run downwind.
These days, yachtsmen do not have to rely on old folklore or gamble on good weather. All sailors should pay attention to weather forecasts. These are available through radio, television, the internet and other means of broadcasting.
The particular forecast that is most appropriate depends on the kind of sailing being planned. The shipping forecast broadcast on the radio is perhaps the most useful to offshore sailors. The terms used in it are precisely defined, and the information that is included in it on pressure changes and movements of weather systems is very useful to anyone with a deeper than average understanding of meteorology.
When yachtsmen study meteorology as part of a training course, either at sea or ashore, they are often asked to create a weather map from a recorded shipping forecast as an exercise. The Royal Yachting Association can provide forms called ‘Metmaps’ that make recording and interpreting the shipping forecast a lot easier. Completing one of these is a good exercise for anyone who wants to go into meteorology seriously. The ‘Metmap’ is a two-sided A4 form. On one side, a shipping bulletin broadcast by the BBC can be taken down. On the other, a simple up-to-date weather map can be drawn from the information contained in the bulletin.
The shipping forecast gives a lot of information about visibility at sea. This is because poor visibility can sometimes be a greater hazard than strong winds. The forecast will not only give a guide to overall visibility in terms of ‘good’, ‘moderate’ or ‘poor’ but will often indicate if visibility is poor for a specific reason, such as ‘visibility poor in showers’. This particular occurrence can give a sailor a real fright, as views of nearby vessels or navigation marks can be lost suddenly when showers occur.
Two possible hazards are not often mentioned in weather forecasts for sailors but usually are in forecasts for land areas:
One of these is lightning, though the possibility of its occurrence may be indicated indirectly in a forecast or station report as ‘thundery showers’. In fact, lightning is not such a risk to sailors as it might at first appear. Boats are surrounded by a very good conductor of electricity – water – and unless the boat suffers a direct hit, which is unlikely, the current is dissipated much more quickly than on land.
The other neglected hazard is exposure to sunlight and sunburn. Sailors are at particular risk for two reasons. First of all, yachtsmen can get an increased dose of sunlight because of reflections from the water. Secondly, they may not notice this because the wind will make them feel cool and unaware they are ‘cooking’. Many a sailor has returned to work on a Monday morning with a ‘yachtsman’s tan’ (from the neck up!). This might seem a nice problem to have, but all sailors should note the example of the America’s Cup crews, who often display extremely colourful suncream to protect against harmful solar radiation.
Despite the apparently long list of hazards described, sailing is, in fact, a very safe sport. It is also a sport where knowledge of meteorology can increase a participant’s enjoyment and even give a competitive advantage!
Acapulco in 1968, sailors competing in the Olympic Games had an unusual surprise from the weather. While not actually hazardous, it was certainly not pleasant. One day, following a sudden squall, the covers of the boats were covered with maggots, which had, presumably, been drawn up into clouds by a whirlwind or waterspout, only to fall out in a downpour of rain.
The year 1979 is famous to yachtsmen for the worst possible reason. In August of that year, during the Fastnet Race (from Cowes on the Isle of Wight to the Fastnet Rock [51°24’N 9°35’W] off south-west Ireland and back again to Plymouth), the fleet of yachts ran into severe storms and rough seas. Fifteen lives were lost. Despite ‘survival conditions’, many crews kept records of the severe conditions, based on their barometers and wind instruments. To the meteorologists who have analysed the Fastnet Storm and its structure, these records have proved invaluable. For a recent analysis of the storm, see the article by D.E.Pedgley in the August 1997 issue of Weather (Volume 52, pp.230-242).
Shipping forecasts are currently broadcast four times a day on BBC Radio 4 Long Wave. They are also available via the websites of the Met Office and the BBC Weather Centre. In shipping forecasts, the Beaufort Scale is used for describing wind strength. This scale originated in the days of sail but is now defined precisely in terms of the wind at a height of ten metres averaged over a ten-minute period.
Every year people go and enjoy the wonders of the mountain scenery but for some the experience isn’t so pleasant as they venture onto the mountain unaware of the weather they may met. Every year, even in the UK people die on mountains as a consequence of the weather.
Some underestimate the mountain weather; some are unaware of the mountain weather and some leave decisions on the weather too late when on the mountainside.
Mountain tops are often hidden by clouds, which can result in people getting lost. But why does this happen? Clouds are formed by the condensation of water vapour in rising air. Air is very moist (holds lots of water) when it is near the sea or when there is persistent rain. In the UK the cloud base (i.e. the bottom of the clouds) is often below 1000m, so low in fact that much of the time the clouds cover the mountain tops. Cloud cover on the mountains is particularly common in the west of the UK where the moist air blows in across the Atlantic. Clouds can be supercooled i.e. water remains as a liquid even when the temperature is below freezing (0°C)! these droplets of water freeze when they hit solid objects such as fences and even people. The soft ice can build up into a think layer, known as rime which can cause as much difficulty for walkers as lying snow.
The rain and snow which falls over mountains tends to come from nimbostratus clouds, and occasionally cumulonimbus clouds, tend to be heavier and longer lasting than over nearby low lying areas. This is because the air is forced to rise over the mountains, causing the air to cool as it rises condensing the water from a gas to liquid; forming more clouds. However strong winds at the mountain top can blown the heavier rain over the mountain top, so the heaviest rain will not necessarily be at the highest point. Waterproof clothing and footwear on mountains is essential as there can be heavy rain, driving winds and mountain streams can become deep quickly. Deep depressions coming in from across the West coast of the UK can bring heavy rain and strong winds to the UK. Snow combined with wind can be life-threatening on a mountain top.
Wind chill on the mountains
The higher up the mountain we climb, the colder and windier it usually gets so that the wind chill factor increases. Warm clothing on the top of mountains is definitely needed. On the Munros (the Scottish mountains with tops above 3000m) it can be 10°C cooler at the top of the mountain in comparison to the valley bottom below. In fact air can cool by 6°C in every 1000m and sometimes as much as 10°C. But why does the air get cooler and windier? It is windy high up in the atmosphere as the effect of gravity is reduced and cooler because air temperatures decrease as you get closer to the poles. Therefore gale force winds are stronger and more common at the top of mountains than at sea level. Winds also get faster around mountains as they do around tall buildings in our towns and cities. Over the Himalayas winds of 150km/hr (approximately 42 metres per second) are not uncommon!
What is a whiteout?
Snow combined with poor visibility in cloud also causes problems because shadows disappear. Navigation becomes almost impossible and can lead to blundering into dangerous places ‘ even over the edges of cliffs. This is known as a ‘whiteout’. If there is already much lying snow and a risk of the cloud base descending onto the hills, many climbers often consider it wise to abandon the trip.
Local winds occur on a small spatial scale, their horizontal dimensions typically several tens to a few hundreds of kilometres. They also tend to be short-lived lasting typically several hours to a day. There are many such winds around the world, some of them cold, some warm, some wet, some dry. There are many hazards associated with the winds.
The main types of local winds are sea breezes and land breezes, Anabatic and katabatic winds, and Foehn winds.
This wind is caused by thermal (heat) processes. Anabatic (upslope) winds occur over slopes which are heated by the sun. Air which is in contact with slopes that are warmed expands upward and cool and sinks over neighbouring valleys (see diagram). Anabatic winds are usually slow, at only 1-2m/s and are rarely important expect near coasts where they can increase the strength of sea breezes.
Katabatic (downslope) winds occur over slopes which are cooled. Katabatic winds occur where air in contact with sloping ground is colder than air at the same level away from the hillside over the valley (see diagram). Katabatic winds are nocturnal phenomena in most parts of the world (i.e. they tend to happen at night) as there is surface cooling, especially when there is little cloud and due to lack of heating by the sun.
Katabatic wind speeds do not typically not exceed 3 or 4 m/s. However, where the ground is covered with snow or ice, katabatic winds can occur at any time of day or night with speeds often reaching 10 m/s, or even more if funnelling through narrow valleys occurs. Katabatic winds may lead to the formation of frost, mist and fog in valleys.
Sea breezes are the result of differential heating of the land and the sea. Sea breezes occur by day, when the land becomes warmer than the sea.
Warm air from the land cannot expand into the sea as the air is cooler and more dense, so it expands up into the atmosphere. Cumulus clouds tend to form as the warm air rises over the land to about 500-1500m.
The diagram below shows the whole sea breeze process.
Air in sea breezes is cool and moist compared to the air over the land. Sea breezes can move 70km inland in temperate climates by 9pm in the evening. Sea breezes can be noticed several kilometres out to sea. In the tropics they can be felt 20km from the land. Wind speeds from sea breezes can be about 4-8m/s but can be even stronger.
Land breezes occur at night and in the early morning, when the land is cooler than the sea. This is because as the air cools in the night time (as there is less heating from the sun) it contracts. Pressure is higher over the land than the sea. This causes the air to flow from the land to the sea which is known as a land breeze. The circulation is completed by air rising and moving towards the land at 100-300m.
This is shown on the diagram below.
Cumulus clouds from where there is rising air. Land sea breeze fronts tend to only affect a small area of 10-15km out to sea, in comparison to the much larger effect of sea breezes. Wind speeds are also lower at 2-3m/s.
As well as local winds and local weather phenomena, the following list includes seasonal winds with local names:
A cold dry wind which blows from the north-east, north or north-west in the mountainous regions of southeastern France and western Switzerland in winter months. The bise is accompanied by heavy cloud.
The bora is a strong, cold and gusty north-easterly wind which descends to the Adriatic Sea from the Dinaric Alps, the mountains behind the Dalmatian coast (the coast of Croatia). It is a winter phenomenon that develops when a slow-moving depression is centred over the Plain of Hungary and western Balkans so that winds are blowing from the east towards the Dinaric Alps. These mountains form a barrier which trap the cold air to the east of them whilst the Adriatic coast remains comparatively mild. Gradually, though, the depth of the cold air increases until the air flows over passes and through valleys to reach the Adriatic Sea.
The bora begins suddenly and without warning and the cold air typically descends to the coast so rapidly that it has little time to warm up.
The bora can reach speeds of more than 100 km/h and has been known to overturn vehicles and blow people off their feet.
The Chinook Wind
A warm, westerly wind found in western North America – Canada and the USA, when air from the Pacific blows over the Rocky Mountains and other upland areas. On January 15th, 1972, the Chinook caused the temperature in Lorna, Montana to rise from -48°C to 9°C in 24 hours! The fastest wind speed recorded during a Chinook was 107mph, in Alberta, Canada.
The name given to the drizzly weather with low stratus, mist or fog which occurs from time to time during the period January to April over the China Sea and in coastal areas between Shanghai and Cape Cambodia. It occurs when cool, moist air from the north encounters warm, moist air, and it is intensified by orographic lifting and/or by coastal convergence.
The Etesians/ Meltemi
The strong northerly winds which blow at times over the Aegean Sea and eastern parts of the Mediterranean Sea during the period May to October. The winds are known as meltemi in Turkey.
The Föhn (or Foehn)
The Föhn is a warm, dry, gusty wind which occurs over the lower slopes on the lee side (the side which is not directly exposed to wind and weather) of a mountain barrier. It is a result of forcing stable air over a mountain barrier. The onset of a Föhn is generally sudden. For example, the temperature may rise more than 10°C in five minutes and the wind strength increase from almost calm to gale force just as quickly. Föhn winds occur quite often in the Alps (where the name Föhn originated) and in the Rockies (where the name chinook is used). They also occur in the Moray Firth and over eastern parts of New Zealand’s South Island. In addition, they occur over eastern Sri Lanka during the south-west monsoon.
The danger of a Föhn where there are steep snow-covered slopes is that avalanches may result from the sudden warming and blustery conditions. In Föhn conditions, relative humidity may fall to less than 30%, causing vegetation and wooden buildings to dry out. This is a long-standing problem in Switzerland, where so many fire disasters have occurred during Föhn conditions that fire-watching is obligatory when a Föhn is blowing.
An explanation of the Föhn effect in the UK from BBC weather.
The Gregale (or Grigale)/ Euroclydon/ Euraquilo
A notorious wind of the western Mediterranean which also blows across central parts of the Mediterranean Sea. It is a strong and cold wind from the north-east and occurs mainly in winter. It is most pronounced on the island of Malta, where it sometimes reaches hurricane force and endangers shipping.
The Bible tells us that the ship which carried St Paul and other prisoners across the Mediterranean en route to Rome was driven by a storm from Crete to Malta, where it was eventually wrecked.
The ship set sail from a bay called Fair Havens near Lasea on the south coast of Crete, having put into this bay to wait for favourable conditions after being delayed by contrary winds. As the bay was exposed to storms, it was not considered a safe place to remain at the time of year in question, which was either late September or early October. The harbour at Phoenix on the south-western coast of Crete was considered a safer place to spend the winter. Soon after the ship left Fair Havens, however, a severe gale began to blow. So violent was the storm that the sailors could do no more than drift with the wind. The Bible tells us that the ship reached Malta fourteen days later.
Paul experienced a gregale. As these winds normally last no more than four or five days, the storm he experienced appears to have been unusually persistent.
A dry and comparatively cool wind which blows from the east or north-east on the coast of North Africa between Cabo Verde and the Gulf of Guinea during the dry season (November to March). It brings dust and sand from the Sahara Desert, often in sufficient quantity to form a thick haze which hinders navigation on rivers. Dust and sand are sometimes carried many hundreds of kilometres out to sea.
The Helm Wind
An easterly wind found in Cumbria, N. England, where the winds blow over Cross Fell and then descend into the Eden Valley. A bank of cloud forms over the hill tops, and the roaring of the wind can be heard as far away as Penrith.
The name given to the south-easterly winds which prevail in winter (December to April) in the Persian Gulf. They are accompanied by gloomy weather, rain and squalls and are sometimes followed by very strong south-westerly winds called suahili.
A hot, dry, dust-laden, southerly wind over Egypt, the Red Sea and eastern parts of the Mediterranean Sea ahead of eastward-moving depressions. It occurs during the period February to June, being most frequent in March and April. The Khamsin is a Sirocco wind, whose name comes from the Arabic word for ‘fifty’, which is approximately the length of time the wind blows for. In the nineteenth Century, the plague was worst in Egypt when the Khamsin was blowing.
A strong south-westerly wind which blows daily over the Gulf of Aden from about 22:00 hours until about noon the following day. It occurs in June, July and August (during the south-west monsoon) and frequently reaches gale force.
A hot, dry, southerly wind which occurs in winter and spring between Madeira and Gibraltar and along the coast of North Africa ahead of an advancing depression.
A moist wind which blows from the east over the Strait of Gibraltar. It is frequently accompanied by haze or fog and may occur at any time of year, though it is most common in the period June to October. A feature is the occurrence of a ‘banner cloud’ extending a kilometre or more downwind from the summit of the Rock of Gibraltar.
The strength of the Levanter does not normally exceed Beaufort Force 5. When it is strong, however, complex and vigorous atmospheric eddies form in the lee of the Rock, causing difficult conditions for yachtsmen and the pilots of aircraft. The levanter can also cause persistently foggy weather on the coast of Spain.
A hot, dry, southerly wind which blows on the south-east coast of Spain ahead of an advancing depression. It is typically laden with sand and dust, and its approach is often heralded by a belt of brownish cloud on the southern horizon.
A strong, squally, south-westerly wind which occurs over central parts of the Mediterranean Sea, most common in winter.
The name given to north-westerly winds over the Adriatic Sea, the Ionian Sea and coastal regions of Sardinia and Corsica.
A strong south-easterly wind over the Golfe du Lion. It is usually accompanied by warm, cloudy weather with rain.
The mistral is also a strong and often violent wind. It blows from the north or north-west down the Rhône Valley of southern France and across the Rhône Delta to the Golfe du Lion and sometimes beyond. Though strongest and most frequent in winter, it may blow at any time of year and develops when stable air is forced through the Rhône Valley. It occurs when a depression is centred over north-west Italy and the Ligurian Sea and a ridge of high pressure extends north-eastward across the Bay of Biscay.
It may blow continuously for a day or two and attain speeds of 100 km/h, causing considerable damage to crops and making driving conditions difficult in the Rhône Valley. It clears clouds and pollution out of the air. In the Rhone valley in France, trees lean to the South because of the force of the Mistral.
This name for a wind is used in more than one place. In Chile, a Norther is a northerly gale with rain. It usually occurs in winter but occasionally occurs at other times of year. Typically, it can be identified by falling air pressure, a cloudy or overcast sky, good visibility and water levels below normal along the coast.
Over the Gulf of Mexico and western parts of the Caribbean Sea, Northers are strong, cool, northerly winds which blow mainly in winter. Over the Gulf of Mexico, they are sometimes humid and accompanied by precipitation, but over the Gulf of Tehuantepec they are dry winds.
The name given to severe line squalls in Argentina and Uruguay, particularly in the Rio de la Plata area. They are associated with marked cold fronts and are usually accompanied by rain, thunder and lightning, a sharp drop in temperature and a sudden change of wind direction from northerly or northwesterly to southerly or south westerly. They are most likely to occur during the period June to September.
Strong westerly winds found in the Southern Hemisphere between 40 and 50 degrees South. Sailing ships have always made use of them. The winds are much stronger in the Southern Hemisphere because there is very little land to slow them down – only Tasmania, New Zealand and the very bottom of South America.
The Santa Ana
A hot, dry, strong, blustery, föhn-type wind which blows from the north-east or east over southern California and carries with it large quantities of dust. It is most frequent in winter but may also occur in spring or autumn. It may get its name from the Santa Ana Mountains or the Santa Ana Canyon but other possibilities are that it derives from santanas, meaning ‘devil winds’, or the Spanish Satanás, meaning Satan. These winds can cause a great deal of damage. As they are hot and dry, they cause vegetation to dry out, so increasing the risk of wildfires; and once fires start the winds fan the flames and hasten the spread of the fires. In spring, Santa Ana winds can cause considerable damage to fruit trees.
Strictly, the shamal is any north-westerly wind over the Persian Gulf and Gulf of Oman, but the term usually refers not to the normal prevailing winds but to the squally gale-force winds accompanied by rain and thunder which occur in winter.
The Scirocco/ Sirocco
A hot, dry wind southerly wind which blows from the Sahara in northern Africa into the southern Mediterranean. It picks up moisture as it crosses the Mediterranean and can reach Spain, France, Italy and Greece bringing Saharan dust and hot, windy, damp weather, often with fog or low stratus cloud. In spring, the Sirocco can bring gale force winds. There are many local names for the Sirocco, including chom, arifi, Simoom, Ghibli, Chili, Khamsin, Solano, Leveche, Marin and Jugo.
An easterly or south-easterly wind, with rain, which occurs in the Strait of Gibraltar and over south-eastern coasts of Spain.
The name given to the violent squalls which are associated with well-defined active cold fronts over coastal regions of southern and south-eastern Australia. They are accompanied by lightning, thunder and gale-force winds and are similar to pamperos. They are most frequent in summer but may also occur in spring and autumn.
These are characteristically squally local winds which occur over the Malacca Strait several times a month during the period April to November. They are always accompanied by heavy rain from cumulonimbus clouds and are almost always accompanied by lightning and thunder. They are initiated by katabatic winds and therefore tend to occur at night.
A violent squally wind from the north or north-east in the Gulf of Tehuantepec in winter. It originates in the Gulf of Mexico as a norther and blows across the Isthmus of Tehuantepec.
The Trade wind
Easterly winds in the Tropics (between the Tropic of Cancer and the Tropic of Capricorn). The Trade winds helped European explorers reach America.
A cold, dry, northerly or north-westerly wind over the coast of Catolina and a cold, dry northerly or north-easterly wind over the west coast of Italy and the north coast of Corsica. It is typically a strong wind but does not often reach gale force.
Strong, squally, south-westerly winds off the east coast of Spain and in the Strait of Gibraltar. They occur mainly during the period September to March and are often accompanied by violent squalls, heavy rain and thunderstorms.
A sudden, cold, violent wind found in Alaska and Cape Horn which blows from the mountains to the sea.
This term applies to two different phenomena. It usually refers to a dry and often dusty föhn wind that occurs over the eastern slopes of the Andes in central Argentina in winter months. It is also the name (or sondo) given to a hot, humid, northerly wind over the Pampas region of South America in advance of an eastward-moving depression and preceding a pampero occurrence.
Sunshine is essential for life on our planet. The existence of all plants, animals and life on land and sea depends on the sun. The movement of the atmosphere and the oceans are powered by the sun. Without sunlight plants would not grow and crops would not ripen. Sunlight in moderation is good for us; it helps us to maintain the balance of vitamins in our bodies and can help us to generate power through the use of solar panels. Many people do not like damp and cloudy weather and this is known as seasonal affective disorder. Black surfaces become hotter than white surfaces in sunlight, so buildings in sunny places tend to be painted white to keep them cooler, and people wear white clothes to keep cool.
Weather forecasters in the UK use the UV (ultra-violet index) to warn about the strength of the radiation from the sun. The index depends on two factors; the position of the sun in the sky and the amount of cloud cover. In the UK a scale of 1 to 10 is provided for the index, combined with risk categories, which basically tell you how harmful the sun is going to be to humans. The sun can burn our skin and hurt our eyes if we look at it directly.
LOW= sun will not prove harmful. MEDIUM= sun is not dangerous but you should not expose bare skin to the skin for over 1-2 hours HIGH= the sun is dangerous and you could burn in 30-60 minutes VERY HIGH= the sun is very dangerous and you could burn in 20-30 minutes
In addition to all of these the sun can cause overheating and dehydration.
Thunder is the loud noise which follows a flash of lightning. Lightning can be seen before thunder is heard as light travels faster than sound. The speed of sound in air is just over 300m/s. This means that if you count the seconds between seeing the lightning and hearing the thunder, and divide by three, you can work out how many kilometres away the storm is (for example, if you start counting when you see the lightning and get to 9, then the storm is about 3km away). The noise of thunder is caused by the rapid expansion of heating the air. You can normally hear thunder up to 6 miles (10km) away from the lightning flash. The sound can last quite a few seconds!
What is lightning?
Lightning can be seen virtually instantaneously as light travels very fast (about 300,000,000 m/s!). Lightning can be seen up to 50 miles away! lightning. Lightning is produced by discharges of electricity from cloud to cloud or from cloud to ground. A large positive charge builds up in the upper part of a thunder cloud and a negative charge builds up near the base of the cloud. When the potential difference between the charged areas becomes large enough, electrical energy is discharged and a flash of lightning occurs. Huge quantities of electricity are discharged in lightning flashes and temperatures of over 30,000°C or more can be reached!
What should you do in a thunderstorm?
In a thunderstorm you should not stand under a tree! Lightning tends to strike the highest point around and everything near this can be a target for the lightning too. Very few people survive being hit by lightning. To increase your safety in a thunderstorm you should avoid high ground, water, open spaces such as parks and golf courses, staying in a tent or shed, being within 30m of wire fences or using your umbrella. You should make yourself as small as possible – curling up in a ball is good. It is however safe to stay in the car…do you know why?! It is because the car acts as what is known as a Faraday cage, protecting you from the electric field generated by the storm.
Who discovered how to protect buildings from lightning?
Benjamin Franklin…in 1752 he flew a kite into a thunderstorm (don’t do this; he put his life at risk!) but luckily he survived and invented the lightning conductor. A lightning conductor is a metal rod or piece of wire which electrical discharges and led harmlessly to earth. They can now be seen on church towers and spires, skyscrapers and other tall building to protect them from damage.
How can a thunderstorm form?
For thunderstorms to occur, cumulonimbus clouds are required. These are heavy, dense, towering clouds with tops shaped like anvils or vast plumes, where the speed of air rising through the cloud can reach 20m/s. Pilots tend to fly around these clouds if they can. They can fly around them as often they are only 10-12km in width. In cumulonimbus clouds weather such as heavy rain, lightning, hail, turbulence and strong winds can occur.
Acid rain Rain that is more acidic than normal because water vapour has condensed on to particles of sulphate or nitrogen oxide.
Advection The transfer of some property (e.g. temperature or moisture) by the horizontal movement of air or water, such as wind or ocean current.
Advection fog Fog caused by the condensation of water vapour when warm, moist air crosses cold ground or sea.
Aerosol A suspension of microscopic liquid and solid particles in the atmosphere for at least a few hours. Can be natural or anthropogenic (man-made).
Air A naturally occurring mixture of gases, chiefly nitrogen and oxygen with small amounts of argon, carbon dioxide and water vapour- we sometimes call this our atmosphere
Airmass A large area of air which has similar temperature and humidity characteristics.
Air pressure The weight of the atmosphere pressing down on the Earth’s surface as a result of gravity.
Altitude The height of the something above sea level. It is usually measured in feet or metres. Sea level is an altitude of 0 m.
Anemometer An instrument for measuring the speed of wind
Anticyclone A large are of high atmospheric pressure, characterised by outward-spiralling winds- a ‘high’. In the northern hemisphere winds rotate around an anticyclone in a clockwise direction.
Atmosphere An envelope of gases surrounding the Earth. The main gases are nitrogen and oxygen, with smaller amounts of other gases such as water vapour, carbon dioxide and methane.
Barometer An instrument for measuring atmospheric pressure
Beaufort scale A scale that indicates wind speed by the effect wind has on familiar objects.
Biofuel Any fuel (liquid, solid or gas) produced from organic matter (matter from animals or plants).
Blizzard Blowing snow reduces surface visibility. There are low temperatures, strong winds and heavy snow.
Celsius A scale of temperature based on one introduced in 1742 by Celsius, a Swedish astronomer and physicist, who divided the interval between the freezing and boiling points of water into 100 parts. The present system, where the freezing point is marked 0 and the boiling point is marked as 100, was introduced by Christin Lyons in 1743.
Climate The long term (often taken as 30 years) average weather pattern of a region.
Cloud A structure formed in the atmosphere by condensed water vapour.
Cold front The boundary between two different air masses where the cold air pushes the warm air out of way and brings colder weather.
Condensation The process by which water vapour becomes liquid water.
Conduction The process of heat transfer through materials by molecular motion.
Convection The process of heat transfer through fluids by means of rising currents.
Coriolis force An effect caused by the Earth’s rotation, which causes winds and currents to follow a curved path across the Earth’s surface- to the right in the northern hemisphere, to the left in the southern hemisphere.
Cyclone A large area of low atmospheric pressure, characterised by inward-spiralling wind often called a ‘low’ or a ‘depression’. Also the name used for a hurricane in the Indian Ocean and Western Pacific.
Depression A low-pressure weather system.
Dew Liquid water that has condensed on to objects at or near the Earth’s surface.
Dew point The temperature below which water droplets can form in the air.
Downburst A strong downdraught of short duration produced by some thunderstorms.
Drizzle Very small droplets of liquid precipitation.
Evaporation The process where liquid water turns into vapour (e.g. a rain puddle may evaporate into water vapour when the sun comes out). It is the opposite of condensation.
Eye Centre of a hurricane
Fahrenheit A scale of temperature introduced in about 1709 by the German Physicist, Fahrenheit, who was the first to use mercury as a thermometric substance. Primary fixed points were the temperatures of a mixture of common salt and ice and the temperature of the human body; with reference to these the freezing point of water was marked 32 degree and the boiling point of water was marked 212 degrees.
Fog Water droplets in the air that reduce visibility to less than 1000m (1100 yards).
Front The boundary between two air masses.
Frost White ice crystals deposited on the surface of objects that have a temperature below the freezing point of water.
Global Warming The increase in global mean temperature, linked to the artificial increase in greenhouse gas concentrations.
Greenhouse Gases Gases which absorb some of the outgoing radiation from Earth and re-emit it back down towards Earth.
Hail Pieces of hard, solid ice falling from clouds.
Hemisphere One half of a sphere. The term is usually applied to regions north or south of the equator or east or west of the Prime (Greenwich) meridian.
High Also known as an anticyclone- an area of high pressure with a system of winds rotating outwards. This usually means dry weather.
Humidity The amount of water vapour in the air. May be absolute or relative.
Hurricane A tropical revolving storm with sustained wind speeds of more than 118km/h (73mph). It is called a hurricane in the North Atlantic, but in other parts of the world it is known as a typhoon or tropical cyclone.
Isobar A line on a map or chart that links points of equal atmospheric pressure.
Jet stream A strong, high level wind that can reach speeds in excess of 320km/h (200mph) – it is usually around 5-10km (3-6 miles) above the ground.
Katabatic wind A wind which blows down a slope.
Latitude Position on the Earth’s surface north or south of the equator.
Lee The side of a mountain, hillside or island what is facing away from the prevailing wind.
Lightning Discharge of static electricity in the atmosphere, usually between the ground and a storm cloud.
Longitude Position on the Earth’s surface east or west of the Greenwich (prime) meridian.
Low Also called a depression- this region of low pressure can mean wet weather- it is the opposite of high pressure or anticyclone.
Meteorologist Someone who makes a scientific study of weather, weather processes and/or the climate.
Meteorology The science of the atmosphere- meteorology embraces both weather and climate and is concerned with all aspects of the Earth’s atmosphere (and those of the planets) and with the interaction between the atmosphere and the surface. The term was first used by Aristotle.
Millibar Unit for measuring air pressure. Now a hectoPascal (hPa) is the standard unit for pressure.
Monsoon The seasonal shift in wind direction that brings alternate very wet and very dry seasons to India and much of South-East Asia and other regions.
Occluded front The combination of warm and cold fronts as a cold front overtakes a warm front. The front develops during the later stage of the life cycle of a frontal depression and is so called because of the associated occluding (shutting off) the warm air from the Earth’s surface.
Precipitation Moisture that is released from the atmosphere as rain, drizzle, hail, sleet or snow.
Radiation Process by which energy travels across space.
Rainbow A rainbow appears when sunlight shines through water droplets in the air. White light is made of seven colours. As the light shines through the water droplets the light is bent. The different colours of light bend by different amounts, so they separate and become visible.
Sea-level The normal level of high tide, used as a baseline for measuring height or depth.
Snowline The vertical limit of snow lying on mountain side throughout the year.
Synoptic chart A map showing large-scale weather patterns in an area at a given time.
Temperature The heat content of the air.
Thunder Sound caused by intense heating of the air by lightning.
Typhoon A name of Chinese origin, meaning ‘great wind’ applied to the intense tropical cyclones which occur in the western Pacific Ocean. They are the same as the hurricanes of the Atlantic Ocean and the cyclones of the Bay of Bengal.
Warm front The boundary between two different air masses where warm air pushes cold air away to bring warmer weather.
Water vapour Water in its gas form. The proportion of water vapour in the air varies with time and place. The dominant greenhouse gas.
Weather The state of the atmosphere (with regard to wind strength and direction, temperature, precipitation and pressure) at a specific time and place.
Subscribe to MetLink updates
Weather and climate resources and events for teachers