‘Beast from The East’ – the science behind Europe’s Siberian chill

The so-called “Beast from the East” has arrived in the UK, bringing unusually cold weather – about 7°C colder

than the historical average for this time of year. Wind chill is making temperatures feel particularly arctic. So how did the Siberian gusts come to arrive on Europe’s doorstep?

The movement of air across the globe, and the weather it brings with it, is governed by three major influences: gravity, the sun, and something called the Coriolis effect. The influence of gravity is simple, constantly pulling air towards the Earth’s surface.

The rise and fall of the sun dictates whether the air stays there. During the day, radiation from the sun heats the Earth, warming air directly above the surface and causing it to rise, leaving behind a region of low pressure (a low density of air particles). As the air rises, it cools and spreads outwards. This mass of air, now denser than the air below it, sinks back down under the force of gravity, and naturally flows back towards the lower pressure region of air, creating a cycle of air circulation. These circulating patterns of wind exist on an intercontinental scale, transporting heat all the way from the tropics to the poles.

However, thanks to the Coriolis effect – the deflection of objects moving in a straight path due to the Earth’s rotation – the winds do not travel directly north or south. To illustrate this effect, imagine a spinning top. Parts of the spinning top closer to the spindle rotate at slower speeds than parts further away, as they have less distance to travel to complete a full circle. Similarly, the equator has to travel much faster than the poles do as the Earth rotates. As air travels north from the equator, its extra momentum compared to the slower rotating land that it is moving over makes it curve across to the east, while air travelling to the south pole curves westward.

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