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# Material for school visits

This page contains material for presenting to primary school children on the subject of weather forecasting and thunderstorms. It was used on 12 March 2013 with Year 3 of St Columba's College, St Albans (a boys' school), and took around 3 hours with a short break. Feel free to reuse the materials below. There are some tips and thoughts on what worked well and what didn't.

Thanks to Chris Westbrook for his tornado slides, to Carole Peubey, Roger Brugge, Rob Thompson and Emma Irvine for their advice and ideas beforehand, and to Mr Bridge and Mrs Brown for their help on the day and suggestions for last-minute changes to the execution of the weather forecasting game.

## Part 1: Weather forecasting

The purpose is to explain why weather forecasting is useful and how weather forecasts are made.

### Measuring the atmosphere

We start looking at how the atmosphere is measured from the ground, using weather balloons and using satellites. Activities:
• Members of the Department of Meteorology can borrow some hand-held anemometers from the laboratory staff, and you can get the children to see what force on the Beaufort scale they can blow. Set all the instruments to mph first, if possible. Note that depending on the age group they may ignore the decimal point on digital instruments and report very high wind speeds.
• Likewise, you can borrow a broken RS92 radiosonde plus an uninflated weather balloon and parachute, and show them the instruments on it.

### Weather forecasting game

This is a primary school version of Richardson's Forecast factory. The children sit in a 5x4 grid (perhaps in pairs depending on the class size), each representing a town in England and Wales. They then make a 24-hour forecast in six timesteps. If this is being done in Reading or St Albans then the interesting question is whether they will get snow tomorrow (and so school might be cancelled). Rather than getting them to do the calculations for Euler's advection scheme (as in the secondary school version), the children simply pass sheets of paper representing the weather in the direction of the wind to their classmates elsewhere on the grid. Each weather sheet indicates the rain or snow that falls in the 4-hour period - they write this down and then at the end add up the 24-hour accumulations of rain and snow for their town. Boundary values need to be fed in at each timestep. Towards the end a tornado, thunderstorm and blizzard enter the domain.

The materials needed are:

My tips are:

• Make sure the arrangement of the grid is very clear to the children, e.g. by sticking tape down on the classroom floor, or if you have small tables by using each table as a town.
• Make sure that at the start all the weather sheets are aligned north-up/south-down so that the children interpret the arrows on the sheets correctly and pass them in the right direction
• To help the children get an idea what's happening in the whole domain, you can ask them at each timestep "hands up who's got rain or snow" or "hands up who's got a temperature of zero or lower" and point out the fronts passing over and the big area of cold area progressing across the country.
• At the end get them to read out their total rain and snow and write them on the "totals" sheet. You can then discuss the warnings that might be issued, e.g. flood warnings for people living near rivers and transport warnings concerning the snow.
• A modification could be to double the rain or snow accumulations in hilly areas due to orographic enhancement, and to explain why this happens.

I've only done this game once and I'm sure it could be improved, so please let me know if you have ideas or your experience of trying it yourself.

## Part 2: Thunderstorms

The purpose is to give the children a feel for how thunderstorms work: why air rises in thunderstorms, how we measure thunderstorms with radar, what a Doppler radar measures, why tornados form, and how lightning forms. This was done with the assistance of several classroom experiments. I didn't do the cloud in a bottle because they had already seen it, but it would be easy to slot in here.

### Experiment 1: A thunderstorm made of cream

The children will be very impressed with this if it works. The animation below is for a 40x25x25 cm tank and the frames are 10 seconds apart:

You need the following equipment (members of the Department of Meteorology can borrow mine if they want):

• A clear plastic tank - for 10-15 pounds you can get one from amazon for keeping pet insects and reptiles.
• Plastic pipettes with a capacity of around 3 ml, available very cheaply from amazon.
• Five polystyrene cups.
• A kettle.
• A pot of single cream.
• An anglepoise desk lamp.
• A piece of black card and a bulldog clip to hold it to the back of the tank.
• Optional: glycerine-based food colouring.

Instructions:

• Fill the tank almost to the top with cold tap water, and clip the black card to the back of the tank with the bulldog clip.
• Use a pipette to inject 10 ml of single cream into a puddle at the bottom of the tank of water.
• Support the tank with four upturned cups and slide a fifth polystyrene cup containing boiling water under the tank beneath the pool of cream. The water must be straight out of boiled kettle - if it comes from a water heater it will be too cool and the convection will not be very intense.
• Illuminate the tank from above with the anglepose lamp (this is very important, otherwise it is much more difficult to see the cloud). The black card behind will help to give good contrast when looking in from the front.
• Optional: when the convection has produced a big anvil cloud and the updrafts are weaker, inject a pipette full of the glycerine-based food colouring at the top of the tank near the front. The audience needs to be watching closely as this will sink and spread-out at the bottom rapidly - this represents a downburst and a gust-front.

There are videos on youtube of this experiment performed with food colouring as the tracer of the initial convection, but my experience is that this is not very impressive: firstly, food colouring doesn't illuminate well so is difficult to see, and secondly you would need a water based one as the glycerine-based ones are too dense and sulk and the base of the tank no matter how much you heat them. Single cream, on the other hand, has the same density as water and is very visible. I've also tried milk and double cream. Milk is a bit too dense, too optically thin, and looks like small particles rather than a cloud. Double cream is worth a try at home, but it is slightly positively buoyant even before you apply the heat so will start to rise of its own accord. It is also very optically thick, so produces impressive cumulus congestus initially but too soon the tank is completely opaque.

To demonstrate a Doppler radar working, I bought a "Bushnell Speedster III" radar gun, which can measure objects moving at more than 10 mph. Members of the Department of Meteorology can borrow this from me if they wish. In class, I got a child to point it at me with the other children behind it looking at the readout, while the teacher, who was with them, threw tennis balls at me and they then measured their speed. I did it with all the children behind the gun, rather than getting them to point it at each other, to avoid complaints from parents worried about the dangers of microwave radiation; note that the gun is powered by two C batteries, so the energy emitted is very small.

In practice the gun looks impressive and the children (especially boys) want to have a go, but in the end it just measures a number so is not hugely exciting.

### Experiment 3a: Conker on a string

The challenge is to explain how a tornado forms - the vortex stretching idea is in the slides, and this comes down to conservation of angular momentum (but best not to use that phrase). This is simply and effectively explained with a conker on a string but with the string also threaded through a piece of plastic tubing (I used the nozzle cap from a canister that goes in a sealant gun, and cut the closed end off) and knotted so that the tubing and the conker will stay on the string. Hold the plastic tubing and spin the conker round using the full length of the string so that the radius of rotation is large. With your other hand, pull the string from the back of the tubing so that the radius of rotation is reduced steadily to zero - the conker will speed up significantly. The children should all want to have a go at this. This may help to explain tornado formation: rising air in the middle of the cloud stretches any rotation below the cloud, which sucks the air inwards - this is like the shortening of the string and it makes the rotation increase.

### Experiment 3b: Tornado in a bottle

This is pretty standard on youtube, but you should expect to find your children are much more enthusiastic than the ones in this clip. My tips are:

• Use lots of glitter rather than dye to make the rotation easily visible
• Don't just remove the caps from the coke bottles before sticking the bottles together because the water will go down too quickly and the tornado will be shortlived. Better to leave the caps on but cut a circular hole in them about 1.5 cm in diameter to restrict the flow and make the tornado last longer. There is a trade-off, however: if the hole is too small then even with a lot of swilling by hand you may find it more difficult to get the tornado to start
• The children will want to have a go but younger groups may well have difficulty getting the spinning motion needed to start the tornado off.

### Experiment 4: Lightning at home

This is also quite well known but is more difficult to pull-off in a classroom context. I did it as described here, except that I picked the aluminium plate up with the pencil before giving myself a shock. It worked fine at home, but for a variety of reasons only about a quarter of the children got a shock:

• They tended to rup the polystyrene (styrofoam) plate so hard it sagged in the middle then was less effective at transfering its charge to the aluminium plate.
• They all wanted to grab the aluminium plate quickly, but a shock will only be felt if the finger is brought to the plate slowly.
• I think many were wearing rubber-soled shoes which didn't help.
I've got a disected woolly jacket (from a charity shop) if anyone in the Department of Meteorology wants to try, but my advice is that this is too unreliable to do in a classroom.