In the first of our series of articles about how the weather affects surfing, we look at what causes our swell in the South West of Britain;

Low pressure systems

As you know the UK is situated on the Eastern side of the North Atlantic Ocean. Out at sea there is  a lot of activity in the weather.  Understanding how the weather works will help you see how waves are formed.

Our UK waves are formed by low pressure systems. To find out about low pressure systems and how they are created, we need to first consider what is happening to air pressure across the world.

No prizes for guessing that the equator is hotter than the rest of the planet, so we can also guess that over the equator the air is heated. This air rises, and is replaced by cooler air from the poles. These pockets of air are called ‘highs’ and ‘ lows’.

Low pressure areas suck in air from hotter areas. When a pocket of warm and cooler air meet the hot air passes over the top, which lowers the pressure, and makes the air spin. Low pressures spin anti-clockwise and highs clockwise. As you can imagine, in winter, when the difference in temperatures is greater, these low pressures are more dynamic and the air spins faster.

In the Atlantic the pattern we see is a low pressure system predominantly coming from the South West heading North East for our Western coastline. Why does it go this way? Well, its all down to the jet-stream. This is the name for the flow of air at high levels in the atmosphere. The jet stream travels faster than the air lower down in our atmosphere, where the highs and lows are moving. The jet stream moves West to East around the world. This movement is caused by the rotation of the Earth. It can be pushed North or South, and can be stronger or weaker, depending on the other weather systems it comes into contact with. Some scientists have said that with climate change these jet streams are being pushed further towards the polar regions.

These highs and lows are often depicted on TV weather charts called ‘synoptic charts’. (We’ll look at these in more detail later in our series.)

So next time you tune in see if you can spot one, and predict which way it is heading!

In our next article we will look at what these low pressure systems are doing to the surface of the ocean.