The Science Behind the Beast from the East – Fiona McBride

As the tail end of February slid into March this year, bitingly cold weather sunk its teeth into the whole of Britain: the Beast from the East had struck. The UK and surrounding areas of the North Atlantic experienced temperatures that were, on average, seven degrees lower than usual for this time of year. So, what are the origins of this icy meteorology – and what is its future?

The weather we experience in Britain originates in the North Polar jetstream – a ribbon of fast-flowing air around 10 km above our heads, that winds its way along the boundary between cold polar air and the warmer air above more southern regions. This is ultimately caused by something called the Coriolis effect: because the earth spins on an axis, the further a point is from the equator, the faster it must spin. Usually, the Coriolis effect sends the UK mild, wet weather systems formed over the Atlantic on a south-westerly prevailing wind.

However, sometimes the jetstream path gets twisted up. Earth’s atmosphere is essentially one big, spherical cloud of air and water, so events in one part can affect the weather across the whole globe. In late January this year, some of the largest and strongest thunderstorms ever recorded struck the tropical west Pacific, sending shockwaves through the atmosphere that stirred up Cyclone Gita, and stormy weather over New Zealand, and disrupted the atmospheric wind patterns above the North Pole. The impact of this was multiple changes of direction to the jet stream, ultimately causing the main airflow direction to change. Cold Arctic air flowed south and snaked across Scandanavia to the relatively low pressure zone above the UK, while the warmer air that usually characterises our home climate caused a 20 degree temperature rise at the North Pole. Although it froze the toes off Britain, this is what lead to the meteorological classification of the Beast from the East as a Sudden Stratospheric Warming Event.

So, the Beast from the East, in all its Arctic glory, flew in on winds from the North Pole that were actually caused on the other side of the globe. Different areas of the UK were impacted to greater or lesser extent as a result of a number of factors: the Southwest of the island was the last to receive the storm clouds, so more of the snow had been released by this point. Cites tend to produce heat, which keeps the air moving and creates a warmer microclimate, so most metropolitan areas experienced slightly higher temperatures and a smaller proportion of snow sticking on the ground. However, built-up areas create wind tunnels along streets, leading to extra strong winds, lowering the temperature most people experience.

The Beast is gone for now, leaving us with milder weather more characteristic of spring – but could it return? The last few weeks represented some of the harshest winter conditions many of us have experienced in a while, and there is a suggestion that this mightn’t be the last of it. Hurricanes, storms, and wildfires have all been occurring across the globe with increasing frequency over the last couple of decades, and Sudden Stratospheric Warming Events such as this one appear to be following a similar pattern. More data is needed, but it appears that the Beast from the East is a snarling, bitingly cold example of climate change across the globe.

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