The jet stream has a lot to answer for – and not just here in the UK
This winter in the UK has been characterised by perpetual storminess that has seen low pressure after low pressure arrive on our shores, bringing disruption and flooding that has continued since the end of December.
The cause of the stormy weather has been the jet stream – the fast-moving ribbon of air five miles up in the atmosphere – that drives the weather that we experience down here at the surface.
It’s been particularly powerful this year thanks to extremely cold air flooding off eastern Canada and colliding with sub-tropical tropical air, boosting it to speeds of 200-230mph.
The jet stream doesn’t only play a big part in creating deep areas of low pressure, but also acts as an atmospheric superhighway – transporting them from one place to another.
With the jet stream being stuck in more or less the same position all winter, it has meant that we’ve been left with a stormy weather pattern for almost two months.
What drives the jet stream?
The jet stream is driven by the huge temperature contrast between the cold poles and warm equator and will often follow the zone where the greatest temperature difference occurs over the shortest distance.
This varies from season to season, with this zone often being north of the UK in late-spring and summer and close to or over the UK during autumn and winter – giving us our most unsettled spells of weather of the year.
As the temperature contrast has been especially strong this winter, the storms that have affected us have been frequent and intense.
Jet stream’s global influence
Across the Atlantic in the US, the jet stream has also been locked in the same position for much of the winter, having different effects on different parts of the country.
The jet stream has been taking a path northwards to the west of the US, before reaching into central Canada and diving southwards across the Midwest.
When the jet stream heads north, it takes warm air with it, as well as forming areas of high pressure. This has led to California suffering from a lack of rain and snow, with 90 per cent of the state in severe drought and 67 per cent extreme drought.
When the jet stream heads south, it takes cold air with it, as well as forming areas of low pressure. This has caused the eastern half of the US to experience its coldest weather in decades, as well as delivering lots of snow.
So, the jet stream being stuck in the same place for long periods of time this winter has brought extremes, albeit of a different nature, to different parts of the world.