What is wind?

Have you ever felt a freezing gust of wind in the wintertime or a warm breeze during the summer? Then you have felt two different types of wind.

But what is wind, and where does it come from?

The Earth has a layer of air around it, called the atmosphere - and it isn’t equally spread. In some places, the atmosphere is thicker – there is more air squeezed in over the ground. We call this high pressure. In some places, the atmosphere is thinner with less air taking up the same space. We call this low pressure.

The differences in air pressure make the air move. A bit like air rushing out of an inflated balloon, the air moves from places with high pressure to places with low pressure. We call this moving air wind. The bigger the difference in air pressure,the faster the wind.

Winds are named by the compass direction they are coming from - north, south, east or west.

Northerlies can be bitterly cold in winter as they are moving cold air from the northern Arctic Regions.

Southerly winds bring in warmer air from Southern Europe or Africa and make the weather warmer. And Westerlies bring rain as the winds carry a lot of moist air full of water vapour from the Atlantic Ocean.

Easterly winds come from over Europe. Because they come from over land instead of the ocean, they bring drier air.

Have you ever noticed that it’s very windy when you’re in a wide open space or on top of a hill? This is because there aren’t as many objects such as buildings, trees, hills and mountains that get in the way of the wind. Any obstacles like these cause friction when the air brushes past them and this slows the wind down.

In the UK the strongest recorded wind was 173mph, it was recorded at Cairngorm summit in Scotland in 1986. You wouldn’t want to get caught inthat!

The windiest place in the world is Antarctica. It can be hard to measure though, because its winds can be so strong that they can destroy the measuring instruments!

When you’re out on a windy day and can feel and see the effects of the wind, try and guess where it’s coming from. Is it a northerly? Is the wind being affected by the buildings or the landscape around you?

KAWSER: There's a strong wind coming across the country today. And if we take a look at the weather map. We can see these white arrows showing the wind coming in from the southwest, spreading across the country.

But why is it so important knowing which direction the wind is coming from? And how do we measure it?

Knowing about wind direction is important for many people and activities. Planes point into the wind to help them take off. Sailors and windsurfers need to know the wind direction, so they can move their sails to be blown in the right direction.

Weather forecasters will try to work out the direction the wind has come from and what weather that will bring.

Wind direction is easy to measure. You can use a weather vane, a wind sock or even a flag or ribbon. Even though we can't see wind, we can see and feel the effects of air moving. Leaves on trees, flags and hair being blown.

Wind direction is worked out using a compass, which shows the directions: north, south, east and west.

A weather vane shows the compass directions and needs to be lined up with the north point on a compass. Weather vanes are usually placed high up on a building or a tall mast, so that other buildings or trees don't get in the way. The wind causes the weather vane to move and point in the direction that the wind is coming from.

If the wind comes from the west, we call it a westerly wind. Westerly winds blow in over the Atlantic Ocean and often bring mild, wet weather. If the wind changes and comes in from the east. It's called an easterly wind. These blow from over mainland Europe and often bring drier weather. If the wind comes from the north, it's a northerly wind and often brings colder weather. And finally, if the wind comes up from the south, it's a southerly wind and will often bring warmer weather.

We can also measure wind direction using a wind sock. You might have seen a wind sock at an airport. Pilots use them to see the wind direction. Windsocks point away from the wind. They also show wind speed. The higher the sock is flying, the stronger the wind is.

PUPIL: Put the wind sock in the air and look at the direction it's pointing.

PUPIL: The wind sock points in the opposite direction from where the wind is coming from. Compare this to a compass to see which direction the wind is coming from.

PUPIL: There is a southwesterly wind today.

KAWSER: So now you know how to measure wind direction, maybe you can find out where the wind is coming from where you are and what weather it might bring with it.