Weather watchers

Gathering information is a very important part of weather forecasting. Before the experts can even begin to work out what the weather is going to be like, they need to know what is happening now. To do this they need a lot of weather information.

The information reaches the Met Office in Exeter throughout the day, where we have very powerful computers which help with the forecasting. The supercomputer in Exeter takes around 90 minutes to make a global forecast for the next five days using all the information it has received

Around the country there are just over 200 meteorological stations which measure elements such as wind speed and direction, air pressure and air temperature. Some make observations every hour, both day and night.

Some 4,000 other land stations from around the world regularly send in information, together with observations from ships and buoys.

Weather information is collected from weather stations around the world, on land and sea, weather balloons carrying radiosondes, aircraft, satellites and weather buoys.

Weather balloons

Information is received from radiosondes. These are small boxes of weather instruments which are carried into the upper air by balloons. The balloons are tracked by radar and send back information on wind speed and direction, temperature, pressure and humidity.
	Fig 1: Weather balloon.

Satellites

Two types of satellite provide information:

Polar satellites
There are two of these operated by the USA which pass around the world in 1 hour 42 minutes at a height of 870 km. During this time they transmit pictures of the Earth. The UK gets images from them twice a day.

Meteosat

Meteosat is the European Geostationary Satellite which sends pictures of Europe and the North Atlantic. The satellite is 36,000 km above the ground and orbits the Earth once every 24 hours. It is geostationary, which means that is stays over the same point on the Earth all the time.

Satellites carry cameras, which take either visible or infrared images of the Earth and clouds. Visible images show what you would see if you were sitting on the satellite looking down on the Earth. Infrared pictures measure the temperature of clouds and ground to form an image.

Weather buoys

	These have been used since 1970. They float in the sea and transmit information back by satellite. Each buoy is about 6 m tall, 3 m wide and weighs over 4.5 tonnes, using solar power to run its electrical systems. Air temperature is measured 2 m above the water, and sea temperature is taken at a depth of 1 m.
Fig 2: Weather buoy.

Let's find out

Make a booklet showing some of the different ways in which weather information is collected.

Based on last week's weather, make your own forecast for the next five days. Draw some pictures to show what it will be like.

Fig 3: Cloudy and snow.	Fig 4: Sunshine and showers.	Fig 5: Sunny.	Fig 6: Thunder and lightning.	Fig 7: Hail showers.

Things to make

Fig 8: Home-made wind vane.

A wind vane.

You will need:

• a pen top;
• card;
• matchsticks;
• plastic lemonade bottle;
• knitting needle.

Cut out an arrow on the card which is 25 cm long. Draw around it and make another the same size.

Take the pen top and glue both of the arrows together as shown in the picture.

Push four of the matchsticks into the cork. Write down and cut out the four points of the compass (N, S, E and W) from the card and stick these to the matchsticks.

Fill the bottle with sand to weigh it down. Push the knitting needle through the cork and balance the pen top on the top of the needle.

Take the vane outside. Find north using a compass and point the north of the vane in that direction.

Take recordings over a period of two weeks to find out which directions the wind tends to blow. Remember that the arrow shows the direction from which the wind is blowing.

Amazing weather facts

In the USA, they have ten Hercules aircraft that have been modified to carry weather-recording equipment. These aircraft are flown directly into hurricanes as they move across the oceans. Weather forecasters take the information from the aircraft to help them accurately forecast the direction the storm is moving over the next few days.

Snowflakes can take as long as one hour to fall to the ground.