Hooked Cirrus

High wispy clouds

Cirrus Uncinus

cirrus uncinusHave you ever noticed clouds like those in the upper part of the picture on the right? They are often seen when a warm or occluded front is approaching, generally 12 hours or more before the front’s precipitation arrives.

The clouds are high in the troposphere, the layer of the atmosphere where precipitation and most clouds occur. They are composed of ice crystals and their height is typically 8 to 10 km. They are called cirrus uncinus (from the Latin cirrus, meaning ‘a curl or tuft of hair’, and uncinus, meaning ‘hooked’). At cloud level, the temperature is typically -40 to -50°C.

Even at temperatures as low as this, the first products of condensation are believed to be water droplets, but the droplets are supercooled and freeze very rapidly. Indeed, they freeze too quickly for clouds of water droplets to become observable. The upcurrents responsible for the cloud formation are slow (typically 5 to 10 cm/s). The fall-speeds of ice crystals are, however, greater than this (50 cm/s or more), so the crystals descend.

Supersaturated Air

Air that is saturated with respect to water is supersaturated with respect to ice. Newly-formed crystals can grow, therefore, even when descending, because they find themselves in air that is supersaturated. Once in air that is not saturated with respect to ice, however, they evaporate as they fall. They then become smaller and smaller and eventually disappear, about a kilometre below the level at which they formed initially. As they become smaller, their descent speed decreases.

When the ice crystals grow, latent heat is released. This warms the air sufficiently (about 0.5°C) for buoyant thermals to form. Thus, cloud regeneration takes place, because additional condensation, and therefore additional ice-crystal formation, occurs in these rising thermals. The small tufts of cloud that are often observed near the heads of cirrus uncinus are formed in this way.

The ice crystals are blown along by the wind, and in the layer where they exist (a kilometre or so deep) wind increases with height. Thus, the tops of the clouds blow ahead of the lower parts, so that hook-shaped streaks of cloud are created. The smallest crystals are blown almost horizontally.

In the upper troposphere, narrow currents of fast-moving air called ‘jet streams’ accompany warm and occluded fronts. They are usually many hundreds of kilometres in length and a few hundreds of kilometres in width, and they contain strong vertical and horizontal wind shears. Vertical shears are typically 5 to 10 m/s per km but can be much more. In the jet streams of middle latitudes, winds are strongest at a height of 9 or 10 km and often exceed 50 m/s, especially in winter. They blow from a westerly point. As the tops of cirrus uncinus clouds blow ahead of the lower parts, the tails of the clouds point towards the west.

Vertical Section through a Warm Front of an Active Depression

Vertical Section through a Warm Front of an Active DepressionWhen an active warm or occluded front approaches a given point, the following sequence of clouds is usually observed: Cirrus uncinus, Cirrostratus, Altostratus, Nimbostratus. Sometimes, the sequence also includes Cirrocumulus and Altocumulus clouds. As the slope of the warm or occluded front is typically 1 in 100 to 1 in 150, Cirrus uncinus clouds normally begin to appear twelve hours or more before the precipitation arrives. The passage of a warm front is marked by a change of cloud type to Stratus or Stratocumulus. The passage of an occluded front is marked by a change from Nimbostratus to Cumulonimbus clouds.

Demonstrations and experiments of supersaturation and supercooling

laboratoryA supersaturated solution contains more than the normal saturation quantity of a solute. Air is therefore supersaturated if it contains more than enough water vapour to saturate it at its current temperature. Because the atmosphere contains condensation nuclei, significant amounts of supersaturation with respect to water rarely occur. As the example overleaf suggests, however, supersaturation with respect to ice occurs quite often.

To demonstrate supersaturation, try the following:

  • Clean an area of a laboratory bench;
  • Place a few small crystals of sodium acetate on this area;
  • Slowly drip a solution of sodium acetate over the crystals.

This should cause a column of crystals to form. The supersaturated solution may be prepared as follows:

  • Place 50g of sodium acetate trihydrate in a small flask;
  • Add 5ml of water and slowly warm the flask;
  • Make sure the solid is completely dissolved;
  • Remove the flask from the heat, cover it with aluminium foil and allow it to cool at room temperature.

Alternatively, a supersaturated solution may be seeded by addition of a small crystal. This will create a solid mass of the chemical.

To demonstrate this:

  • Half fill a glass with crystals of sodium thiosulphate (Na2S2O3);
  • Heat the glass in a bath of hot water until the crystals melt to form a transparent liquid;
  • Filter out any impurities using a funnel and cotton;
  • Cover the glass and allow the liquid to cool to room temperature;
  • Shake the glass, whereupon the liquid freezes immediately

Notice that the glass feels warm.

Sodium thiosulphate freezes at a temperature of 48°C. Thus, a solution of this chemical is supercooled when at room temperature (around 20°C). The shaking of the glass, or the addition of a small crystal, triggers the freezing process. When freezing occurs, latent heat is released and the glass is therefore warmed.

Fog

What is the difference between fog and mist and other fog questions.

Fog is literally a cloud on the ground. It can cover vast areas and comes in a variety of types, just like clouds do. Fogs seen over the sea are different to those found in valley lowland areas and over mountains for example.

Download fog fact file for printing, or have a look at our Experiments and Demonstrations page for experiments which demonstrate how clouds can look dark from below but white from above, or how to make a hygrometer to measure air humidity.For a deeper understanding of how and where clouds form, have a look at our exercise using height/ temperature graphs to investigate atmospheric stability, lapse rates and cloud formation with a worksheet for students with an introductory PowerPoint or this paper.

Why is fog different to mist?
The density of fog and mist are different. In fog the distance you can see (known as visibility) is less than 1km, but in mist the visibility distance can be 1km-2km.

Radiation Fog

When does this type of fog form?

radiation fogThis kind of fog forms when the sky is clear and the wind speeds are low (1-5 kilometres per hour). This type of fog usually forms at night and dissipates (disappears) during the day. In mid-winter, however, particularly in latitudes where the sun is low in the sky (e.g. north-west Europe), it may stay all day. It commonly forms in the dips with sources of moisture such as streams and rivers. Radiation fog is particularly common in autumn and winter in the UK.

What is the science behind this type of fog?

dew on a leafWhen the sky is clear at night, land surfaces radiate heat to space and therefore cool.Sea and lake surfaces do not, however, cool by more than a small amount overnight (much less than 1°C). If the air in contact with a surface is cooled to its dew-point temperature, small water droplets form (condensation). If there is no wind, droplets of dew form on, for example, grass. If there is a very gentle breeze, the tiny water droplets are stirred upwards to form a shallow layer of radiation fog, as in the picture of fog at Cardiff shown. Fog can reach 30m high in some cases. This type of fog does not form over the sea because the temperature of the sea’s surface stays much the same day and night. During the day, the sun’s rays heat the ground beneath the fog. Most of the rays are actually reflected from the top of the fog but some reach the surface, otherwise it would not be daylight in the fog! The ground is gradually heated until the dew-point temperature is exceeded. The fog then dissipates (disappears), often very quickly.

Steam Fog

When does this type of fog form?
thermometerThis kind of fog forms when cold air flows over water that is more than 9° or 10°C warmer than the air. Over sea water, steam fog is called sea smoke.

What is the science behind this type of fog?
sea smokeCondensation results mainly from the cold air mixing with the air that is in contact with the water surface. However, convection also occurs, because the water is so much warmer than the overlying air. This convection causes the mixed air to rise a metre or more, thus enhancing the process of fog formation. Because of the convection, the water appears to ‘steam’. The photo shown was taken in the Canadian province of Quebec.

morning sunrise1. Morning sunrise- the sun’s rays heat the ground beneath the fog and the water droplets evaporate to become water vapour. This effect spreads up through the fog and the fog dissipates. This is often called ‘burning off the fog’.
strong winds2. Strong winds- these can cause turbulence within the fog and disperse the water droplets.

Cumulus Clouds and Fog

Related discussion

coastal fog and cumulus cloudsThe picture shows a view south over Poolewe, north-west Scotland. It was taken at 14:00 UTC on 10 June 1963 and shows something unusual: coastal fog coexisting with cumulus clouds.

For several days, an anticyclone had been centred near Iceland, giving sunny days and light north-easterly winds over Scotland. At low levels, air had travelled to north-west Scotland from well to the north of the Shetland Islands. In this air’s source region, the temperature of the sea’s surface was about 10°C. As the air travelled southwards, it was moistened considerably.

Radiation cooling into the clear skies of the anticyclone favoured fog formation at night over the moister part of the land, but the sun dispersed the fog rapidly by day, except on the coast, where it persisted until early evening. An increase in fog depth occurred over Loch Maree (left-hand side of the picture). The flow of the cool air that maintained the fog was disturbed by a small island (Isle of Ewe), thus causing the water on the bottom right of the picture to be clear of fog.

Cumulus clouds began to form over Beinn Eighe (1009 m) and Beinn Alligin (985 m) around 10:00 UTC, when the sun had warmed the slopes sufficiently. Examination of the 12:00 UTC upper-air temperature and humidity profiles measured at Stornoway (a meteorological station roughly 100 km north-west of Poolewe), shows that a temperature of about 22°C was necessary on the slopes to start cumulus convection. Until this temperature was reached, air over the hillsides did not become warm enough to penetrate the anticyclone’s inversion. Over the sea, where there was virtually no heating of the low-level air, the inversion persisted. The temperature of the sea varies little between day and night, even on the sunniest of days. In contrast to land surfaces, water heats up very slowly. The reasons are that (a) water has a large thermal capacity (b) water moves around, whereas land does not (c) water evaporates (d) sunlight penetrates much farther into water than into the surface of land.

Rime and Glaze

rimeWhen fog occurs at temperatures below 0°C, its water droplets are supercooled, i.e. they exist in the liquid state at a temperature below the normal freezing point. When these droplets strike obstacles such as fences, masts or vegetation, they freeze almost instantaneously to form milky opaque deposits of ice crystals on the windward sides of the obstacles. These deposits are called rime. In the British Isles, supercooled fogs are uncommon at low levels. They occur much more frequently on the tops of hills and mountains.

Glaze is the name given to a coating of ice that forms on objects when supercooled water or drizzle droplets fall on them and freeze. The ice can become thick enough to bring down telegraph wires and power cables. Glaze on a road surface can be extremely dangerous, as the layer of ice (called ‘black ice’) is typically thin, hard and transparent. The road appears to be wet, rather than ice-covered.

fog signCool air tends to flow downhill. Accordingly, radiation fog is most likely to be encountered in dips, especially where there is a stream or river and therefore a source of moisture.

A motorist driving along a fog-free stretch of motorway is legally entitled to drive at 70 mph, except where otherwise indicated. If the motorist suddenly encounters fog, the immediate instinct is to brake. If another vehicle is following too closely, a collision may occur. Remember that the driver who is following does not react instantaneously to the brake lights of the vehicle in front. There is a reaction time, which is short if the driver is alert but may nevertheless be sufficient to make a collision inevitable. Once two vehicles have collided and come to a halt in fog, the likelihood of a multiple collision is great.

Some discussion points and questions

Even if drivers obeyed the Highway Code in respect of safe distances between vehicles, motorway pile-ups in radiation fog might still occur, given that reaction time has to be taken into account.
Given the patchy, unpredictable nature of radiation fog, signs that warn of fog may not be effective. Such signs cannot provide information on precisely where fog is present.
Mandatory speed limits on motorways where fog was known to be present would be ignored by drivers on fog-free stretches, for they would see no reason to obey them
Which are the most fog-free stretches of motorway in the UK, and why?
Can motorway pile-ups in radiation fog be prevented? If so, how?

Cumulus Clouds

Typical Summer Clouds

Related Demonstrations and Experiments 

cumulus cloudsClouds like those in the picture to the right are very commonly observed. They are called ‘cumulus’ because they have a heaped-up form (from the Latin cumulus, meaning ‘heap’). When their vertical extent is small, they are called ‘cumulus humilis’ or ‘fair-weather cumulus’. When their vertical extent is such that cloud width appears to be about the same as cloud height, they are called ‘cumulus mediocris’. When they are taller than that, they are called ‘cumulus congestus’. The tops of cumulus clouds often resemble cauliflowers.

The towering clouds that produce showers of rain, snow and/or hail are called ‘cumulonimbus’ (from the Latin nimbus, meaning ‘rainy cloud’). The tops of these clouds are often anvil-shaped, as shown in the picture below.cumulonimbus clouds

Cumulus clouds are manifestations of convection. They form when bubbles of buoyant air rise.cumulo nimbus

These bubbles, called ‘thermals’, form over ‘thermal sources’ such as concrete, bare sand and rocky hillsides, which become warmer on sunny days than surrounding areas of grass or forest. As the bubbles rise, the air inside them cools, because of adiabatic expansion. The rate of cooling is 9.8°C per kilometre of ascent. If bubbles rise far enough, the air inside them cools sufficiently for saturation to occur, at a height called the ‘condensation level’. Above this level (i.e. inside the cloud), the latent heat that is released when condensation occurs reduces the rate of cooling to about 6°C per kilometre.

The height at which condensation occurs depends upon the temperature and dew-point of the surface air. If this air is moist, the condensation level is low. In the British Isles in winter, it is typically at a height of about 600 metres. On a summer afternoon, it is typically at a height of 1,200 m or more. Over deserts, surface air is often so dry that saturation does not occur at all, even when convection is vigorous enough to lift air to substantial heights.

clouds spread out sidewaysConvection is controlled by buoyancy relative to a thermal’s surroundings. When ascending bubbles encounter an ‘inversion’, a layer where temperature increases with height, they tend to lose their relative buoyancy and spread out sideways, as shown in the picture to the right.. As cumulus clouds grow higher, their tops become colder. Eventually, when a temperature of about -10°C is reached, the water droplets of the cloud (which are by then supercooled) begin to freeze and become ice crystals. The anvils of cumulonimbus clouds are composed predominantly of ice crystals.

Experiments

Convection Currents in a Cup of Tea

cup of teaInstead of tea, we heat a beaker of water. First, we put a small crystal of potassium permanganate in a beaker of water. Then (right), we heat the beaker with a bunsen burner positioned under the crystal. Currents should form in the water. Can you explain these currents? How can you demonstrate convection currents in a cup of tea?

Convection Currents in the Field

Cumulus clouds sometimes occur over the cooling towers of power stations or downwind of them. How do they form? Clue: Large volumes of buoyant moist air rise from the cooling towers of power stations. Cumulus clouds may be seen above forest fires, factory chimneys and other sources of hot air (see picture on the right). Insects are lifted and birds and gliders can soar in the rising air beneath cumulus clouds. How fast does the air rise? Answer: About 1 m/s under a fair-weather cumulus, maybe 4 or 5 m/s under a cumulus congestus cloud. Air can rise at 10 m/s or more beneath and inside vigorous cumulonimbus clouds. What does it feel like to ascend at (a) 1 m/s (b) 10 m/s? Relate to the speed a lift ascends. To work out the speed, divide the height the lift rises when it goes from one floor to another by the time taken to travel that height. Question: Is it safe for birds, gliders or, indeed, any other aircraft to be caught in the upcurrents of cumulonimbus clouds?

Contrails

What are contrails and where do they come from?

ContrailsContrails are trails of ice crystals left in the wakes of jet aircraft. These condensation trails (known as ‘contrails’) sometimes persist for many minutes or even hours. On other occasions, they disappear quite quickly.

Download contrails fact file for printing

What is the Science behind Contrails?

Aircraft and contrailsThe exhausts of aircraft engines are hot and moist. The water vapour in them comes mostly from combustion of hydrogen in the aircraft’s fuel. Behind an aircraft, exhaust gases cool rapidly, mainly from mixing with their surroundings but also to a small extent as a result of radiation loss. This cooling takes a finite (small) time (a fraction of a second), so there is normally a gap of some 50 to 100 m behind an aircraft before a contrail appears. The water droplets that are produced freeze very rapidly if the temperature is low enough. The resulting trails of ice crystals persist and spread if the atmosphere at contrail level is moist enough.

Contrails (and water droplets) form when the saturation vapour pressure with respect to liquid water is exceeded. They persist when the air is saturated or supersaturated with respect to ice.

 

What is Supercooling and how does it affect the formation of Contrails?

Supercooling is a normal occurrence in the atmosphere. Clouds composed of water droplets can persist at temperatures well below 0°C, even at temperatures below -30°C. At temperatures below about -40°C, however, all cloud droplets freeze very quickly. On long-haul routes, commercial aircraft usually reach altitudes of 10 to 12 km, where temperatures are typically below -40°C. Planes on these routes therefore tend to leave contrails behind them. Over the British Isles, trails rarely form below about 8 km in summer, 6 km in winter. When the weather is as cold as it often is in mid-winter in Alaska, Siberia and central Canada, contrails can even form at ground level. Indeed, airfields in these regions have sometimes had to be closed when low-level clouds (ice fogs) composed of aircraft-generated ice crystals have proved persistent.

How do Contrails Disappear?

CirrusOnce formed, contrails are distorted by upper winds and spread by diffusion. Persistent contrails often form large patches of cloud that look like cirrus, cirrocumulus or cirrostratus. Sometimes old contrails sometimes cannot be distinguished from these clouds. Image below: Contrails, to the right: Cirrus. For more information about identifying clouds please see the Cloudwheel (link to the right).Contrails

WOW

The Met Office’s Weather Observations Website (WOW) is a rich source of weather data for locations in the UK and worldwide. 

Here  are some lesson resources which can be used in conjunction with the data:

 

KS2/ Upper Primary

Using data to record and interpret the weather 

11+

A simple and effective lesson plan which uses WOW data to identify Urban Heat Islands

Using weather data to investigate whether sports events can go ahead

Using WOW data to investigate a depression passing across the UK with notes for teachers.

14+

Use WOW data to track a cold front across the UK and work out its speed.

Using WOW data to investigate the weather associated with different air masses on UK weather with  teachers notes. (Find an introduction to Air Masses)

Met Office resource looking at correlation between classroom behaviour and weather 

Help and Hints for Observing

Introduction

With a bit of care and a few precautions, weather observations can be made quite accurately at school or home. This page contains guidance and advice on how observations should be made.

However simple your weather instruments, you can make weather observations.

You should try to make your weather observations at the same time each day. You need to decide in advance what time suits you best and then stick to it as closely as you can from day to day.

Wind force

You do not need equipment for measuring the strength of the wind. You can estimate the strength by means of the Beaufort Scale. All you need to do is observe the effects of the wind on leaves, dust, smoke, flags, etc.

If you have a device for measuring wind speed (called an anemometer), you can use the Beaufort Scale to convert speed to force.

Wind direction

When you measure wind direction, you should do so in an open area. Wind gets funnelled between buildings and hedges and deflected when it flows around and over buildings and other obstacles.

To gauge wind direction, you need some sort of indicator. This may be, for example, a home-made wind sock (to view one, click on home-made wind vane) or a flag or pointer on top of a pole or building. You can also use soap bubbles to indicate wind direction. Ignore the movements of clouds; wind direction normally changes with height.

If you are using a hand-held device to measure either wind direction or wind speed, make sure you are not standing between the device and the direction from which the wind is blowing.

Please note that wind direction is the direction from which the wind is blowing. If, for example, the wind is blowing from the south, you have a southerly wind. If it is blowing from the west, you have a westerly wind.

When the wind is very light, the direction may vary.

Current temperature

You are endeavouring to measure air temperature. Therefore, you must make sure the sun does not shine on your thermometer. Ideally, you should place it in a louvred screen, i.e. a screen which has slats to allow the air to circulate around the thermometer. Do not place a thermometer too near a building, because walls retain heat. The walls can heat up the air nearby so that it is warmer than the air circulating over an open area such as a school playing field.

Maximum and minimum temperature

Do not forget to reset your maximum and minimum thermometers each day. The highest temperature of the day normally occurs during the early afternoon and the lowest near dawn, though exceptions occur in certain weather circumstances (when a belt of rain arrives, for example).

You should reset your thermometers at the same time each day. A good time is 09:00 (9 a.m.) Local Time. If you choose that time, you should remember that the maximum temperature you record will be the maximum since 9 a.m. the previous day and probably occurred during the afternoon of the previous day. The minimum temperature recorded at 9 a.m. probably occurred around dawn on the day in question.

You must make sure your minimum thermometer is not exposed to the sky at night. If it is, it will lose heat to space and thus give a temperature reading that is too low – maybe several degrees too low on a clear night. To measure the minimum air temperature, you need to shade the thermometer whilst still allowing air to circulate around it. Ideally, both maximum and minimum thermometers should be placed inside a louvred screen.

When you record maximum and minimum temperatures, consider whether or not the figures you have obtained are reasonable. Was the maximum temperature yesterday really as high/low as that? Was the minimum temperature this morning really that low? Were the temperatures you measured today higher or lower than the highest and lowest ever recorded in your part of the world at this time of year?

Another useful check is that the maximum temperature should be higher than the ‘current temperature’ readings of both yesterday and today. The minimum temperature should be lower than these readings.

If you are making more than one observation a day, you should report maximum temperature, minimum temperature and rainfall amount only once each day. You should reset maximum and minimum thermometers and empty rain gauges only once each day.

Rainfall

Do not place your rain gauge too near a wall, tree, hedge or fence, and do not forget to empty your gauge each day.

As with maximum and minimum temperatures, consider whether or not the rainfall amount you measured over the past 24 hours was reasonable. Was the amount you measured really that great? Was there really that much rain yesterday? What was the greatest amount ever recorded in 24 hours in your part of the world?

Relative humidity

If you are using a wet- and dry- bulb thermometer, do not forget to top up the reservoir of the wet-bulb – and do so with pure water. Use can then be made of a set of meteorological tables to compute the relative humidity.

If the temperature is below 0°C, special care needs to be taken because the ‘wet-bulb’ will probably be dry at the time of observation. If you can, brush a small amount of pure water over the cloth of the wet-bulb about 20-30 minutes before making the observation. This will allow evaporation to take place and cool the bulb, thus giving you an ‘ice-bulb’ reading.

 

Barometric pressure

How do you set a barometer, and why do you need to set it?

How do you find out what the barometric pressure is near you? To obtain weather observations, including pressure values, from many hundreds of places around the world, click here. For places in the United States, choose a state from the drop-down menu and then, by means of the Go button and “Select a location”, choose a place in that state. For places not in the USA, select a country from the drop-down menu under the heading “International Weather Conditions” and then choose a place in that country.

To go directly to stations in the UK, click here and select a location.

Cloud amount and type

If you cannot see the sky because of fog, haze, dust, smoke, etc, record 8 eighths of cloud (8 oktas) and that the sky was obscured.

If you cannot distinguish cloud type during hours of darkness, record “No reading made”.

For assistance over cloud recognition, go to our cloud key. If you would like to buy a cloud identification chart, which is a laminated card for use in the field, click on Buy a cloudchart from the Royal Meteorological Society’s online shop.

Automatic weather stations and electronic instruments

Care is needed when using automatic weather stations or electronic instruments (particularly electronic thermometers). Readings need to be checked. This is very important, as these weather stations and electronic instruments can give readings that are significantly in error. For guidance and advice on the use of automatic weather stations and electronic instruments, click here.

Automatic rain gauges must be reset each day. So, too, must maximum and minimum thermometers. Maximum temperatures generally occur in the early afternoon and minimum temperatures in the early morning.

Converting meteorological units

To convert a Fahrenheit temperature reading to Celsius: first deduct 32 and then multiply the value you get by 5/9.
Thus: 59°F = (59-32)x5/9 = 27×5/9 = 15°C.
To convert a Celsius temperature reading to Fahrenheit: first multiply by 9/5 and then add 32.
Thus: 20°C = (20×9/5)+32 = 36+32 = 68°F.

To convert inches to millimetres and vice versa:
1 inch = 25.4 mm and 1 mm = 0.03937 inch.

To convert barometric pressure units:
millibars = inches times 33.8639, so 30 inches = 1015.9 mb and 1000 mb = 29.53 inches;
millibars = millimetres times 1.3332, so 760 mm = 1013.23 mb and 1000 mb = 750.1 mm.

To convert wind-speed units:
[kt = knot; m/s = metres per second; kph = kilometres per hour; mph = miles per hour]
1 kt = 0.515 m/s and 1 m/s = 1.94 kt;
1 kt = 1.853 kph, so 1 kph = 0.54 kt;
1 kt = 1.152 mph, so 1 mph = 0.87 kt.

Observations and Data

Weather and climate data sources and resources to support schools making their own observations.

 

Other Useful Links

Contour Drawing

If you’ve ever looked at an Ordnance Survey Map, you’ll have seen the contours – lines joining places which are the same height above sea level. You can spot high places, low places and places where the slopes are steep. The contours are drawn at equal intervals – there might be one every 5m or 10m.

But contour maps are useful for many things other than height. In meteorology, isobars link places where the atmospheric pressure is the same, we use isotherms for temperature, isotachs for wind speed and isohyets for rainfall.

How do you go about creating a contour map from a set of observations? 

Here are a few practise resources:

Isotherm and Isobar drawing exercise based on a depression: student worksheet. A simpler version of the T/ isotherm map can be found here or a complete depression based exercise where students draw contours of temperature, pressure and precipitation to work out what the system looks like: Student worksheets and
notes for teachers.

Urban heat island isotherm drawing exercise:notes for teachers, idealised weather station data for isotherm drawingsatellite image of Birmingham and solution for teachers.

Interpreting isotherms

Drawing isolines on WOW data from depression EVA

Isoline mapping Exercise

Isotherm – Notes for Teachers

Other Useful Links

A beginners Guide from the Ordnance Survey.

Weather Stations

Automatic Weather Stations

An automatic weather station usually consists of a number of outdoor weather sensors which communicate with a display unit indoors, which can in turn often be linked into a PC to store and display data. The link between the instruments outdoors and the display inside can be wireless, although the range will be 100m at best.

A weather station for your school – guidance for setting up a school weather station: Why you need one; what to buy; where to put it; what to do with the data.

What can I use my school weather station for?

If you would like to submit high quality weather observations to a UK network, try the Met Office Weather Observations Website or COL.

Some specific lesson ideas:

Several resources at all levels based on using weather station data from the WOW website

KS2/3 science: Use automatic weather station data together with the Met Office resources to study the difference between day and night and to look at the seasons .

KS3/ 5 geography or maths: Use automatic weather station data to see whether there is a relationship between air pressure and rainfall amount. Does most of our rainfall in the UK occur when the pressure is low?

KS 4/5 geography, science or maths: Does it rain more at weekends? An experiment trialled at Manchester Science Festival

KS3/ 4 science or geography: fieldwork ideas for teachers and students Red sky.pdf with an introductory concept cartoon from the ASE.(The full workbook may be purchased at http://www.amazon.co.uk/Edexcel-Level-Projects-Student-Extended/dp/1846903645)

KS3/ 5 geography: look at the current wind speed and direction (you could also use WOW data for this). How do they relate to the orientation and spacing of the isobars on the current analysis chart? This could be used in conjunction with the introduction to weather maps.

What are other schools using their weather stations for?

Have a look at the websites of
Pitsford Hall school weather station
Reigate Grammar School 
Maiden Erlegh School

London grid for learning together with curriculum links

Why have an automatic weather station?

There are many advantages to an automatic weather station. Weather observations can be made more quickly and conveniently. The sensors can be placed well out of the way and reduce the chances of vandalism – and (in the case of wind measurements, for example) in a better exposed location than would be possible with manual instruments. With a PC link, the data can be used for all sorts of projects, from simple averaging ones to looking at correlations between different measurements such as wind direction and temperature. The main disadvantage of an automatic weather station is that it removes the observer from the real elements being measured, and so the experience of what -5ºC temperatures or 30 knot winds feel like, is lost.

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