Wind

Wind is air moving from places of high pressure to places of low pressure. Like water running downhill, air flows from where there is more to where there is less.

We describe wind by its speed and its direction. A strong wind off the sea and one from the desert are very different.

Who needs wind data?

• weather forecasters
• pilots and sailors: wind affects flying and sailing a lot
• farmers: wind direction hints where rain will come from, and strong wind dries the soil faster

Wind vane (weather vane): an arm that turns, with a pointer at one end and a broad tail at the other. The wind pushes the tail away, so the pointer swings round to face into the wind. Even a light breeze moves it. At airports, a fabric wind sock does the same job for pilots taking off and landing; factories that give off ash or gas use them too.

Anemometer: three or four cups spin on an upright rod. The stronger the wind, the faster they spin. A meter counts the spins and gives the speed in kilometres per hour (km/h).