Last weekend, at 4am on Saturday a thermometer at Switzerland’s Glattalp weather station 1,900m above sea level plunged to -44 degrees Celsius, the coldest temperature ever recorded in Switzerland.
However, the record was disqualified because the thermometer was not in the open air at 2 metres from the ground. Instead it was buried under snow.
The coldest qualifying temperature ever recorded in Switzerland remains -41.8 degrees Celsius, recorded at La Brévine (1,043m) in 1987.
The freezing temperatures in Europe and North America were associated with a sudden stratospheric warming about 30 km over the North Pole. The polar vortex, a body of cold air surrounding the north pole, is normally held in place by a swirling westerly jet stream. However, when this jet stream weakens it allows cold air from the polar vortex to spill out into Europe and North America and for warmer air to enter the Arctic. The effect is sometimes called a wandering polar vortex.
Some meteorologists believe climate change is be behind the weakening jet stream, which is partly driven by temperature differences between the pole and the equator – the Earth’s rotation also drives it. However, as polar ice melts, it is reducing this temperature differential, leading the jet stream to weaken and the polar vortex to wander.