A “sudden stratospheric warming” event took place in early January 2021, according to the UK National Weather Service Met Office. These phenomena are some of the extremes of atmospheric phenomena and I study them as part of my academic research. The stratosphere is about 10 to 50 kilometers above the surface of the earth, with atmospheric levels and sudden warming leading to severe winter weather in Europe and Siberia, increasing the likelihood of snowstorms. In winter the Polar Regions are dark 24 hours a day and so the stratosphere of the northern polar region drops to -60 ℃ or less. The pole is surrounded by strong westerly winds, known as polar vortices, a common occurrence that develops every winter.
However, about six times in a decade this vortex can break in a dramatic fashion, it can raise the temperature at the poles to 50 degrees Celsius in a few days, even though the temperature is so low that they still remain below freezing. The average wind direction around the pole may also be reversed, in which case a “sudden stratospheric warming” event has occurred. The disruption in the stratosphere can then be transmitted downwards through the atmosphere. If this instability reaches the lower levels of the atmosphere, it can affect the flow of jets, a stream of air that usually blows eastward around the planet, splitting the cool polar air from the hot air to the south.
Where the jet stream crosses the Atlantic it usually points to the British Isles but sudden stratospheric warming can move it to the equatorial region. As air currents are temporarily rearranged, warmer Atlantic winds are replaced by cooler winds from Siberia or the Arctic, and Europe and North Asia may experience unusually cold weather.
Where the jet stream crosses the Atlantic it usually points to the British Isles but sudden stratospheric warming can move it to the equatorial region. As air currents are temporarily rearranged, warmer Atlantic winds are replaced by cooler winds from Siberia or the Arctic, and Europe and North Asia may experience unusually cold weather. When the infamous “Beast of the East” crossed Europe in 2018, there were dozens of snowstorms and dozens of deaths.
The effects of stratospheric warming may take several weeks to reach the surface, or the process may take several days. These events are hard to predict in advance. Some can be predicted a few days in advance while others can predict about two weeks in advance. Several factors, including the La Nina event in the tropical Pacific region, contributed to a strong cyclone in early winter 2020/21. Strong vortices are hard to transfer, meaning the sudden stratospheric warming event probably didn’t show up very likely. However, just before Christmas, the weather forecast model began to transform into a potential stratospheric warming event in early January.
