Every winter in the Northern Hemisphere, a cold wind circles the North Pole like water around a drain. This is an annual weather pattern that meteorologists are watching – any significant changes may indicate that Europe is seriously cold. At the moment, the wind is tearing in two.
Researchers from the universities of Bristol, Exeter and Bath have devised a new way to predict the effects of various changes to this large airflow high in the stratosphere, 10 to 50 kilometers (6 to 30 miles) above. .
Ironically, the cause of this cold fever is a sudden heat eruption that seeps into the swirling currents over a window of just 24 to 48 hours.
As the temperature rises by as much as 40 degrees Celsius, the vortex undergoes rapid changes, changes course or erupts dramatically in daughter vortices that move against the surrounding atmosphere.
The results can be devastating. Only a few years ago, a sudden stratospheric warming (SSW) pushed an icy polar air from Siberia into Europe, delivering a snow-laden cell under high pressure that the media called The Beast from the East.
Centered across Scandinavia, the shock of icy weather has shed a frozen light as far as the west of the UK, helping to transport chaos and even a number of deaths.
That said, not all shifts in this polar vortex end in freezing conditions. Two years ago, the warming of the stratospheric polar winds was one of the warmest winter days in the history of the United Kingdom.
Knowing which deviations are the most important from the rage in winter, and which will fizzle, will go a long way in making weather forecasts more accurate.
Surprisingly, such stratospheric warming events themselves are not exactly rare, and records indicate that on average about half a dozen of them occur in the Arctic vortex every decade.
“While extreme cold weather is not a certainty, about two-thirds of SSWs have a significant impact on surface weather,” said Richard Hall, meteorologist at the University of Bristol and lead author of the new study.
Observations dating back more than six decades, the researchers provided 40 such examples of oscillation and tearing in the northern stratospheric polar vortex, which informs a detection algorithm that attempts to predict the impact that each type of change will have on weather systems in the northern hemisphere. . .
The results suggest that every time the polar vortex is divided into two smaller winds, we can expect worse cooling events compared to other SSW variances.
This is a timely result, with predicted changes to the air currents appearing over the weekend.
“As predicted, atmospheric observations now indicate that the Arctic stratosphere is experiencing a sudden warming event associated with a weakening stratospheric polar vortex,” said Adam Scaife, head of long-range forecasting at the British Met Office.
What’s more, the change has all the hallmarks of the more dangerous type of SSW, meaning the chances are high that the predicted drop in temperature will be significant.
Having informed climate models can definitely improve your chances of knowing what to expect. But while modeling on this scale benefits from improved algorithms, there is still room for much uncertainty when it comes to nailing down the exact details in the coming days.
Oddly enough, it may even seem that Europe is sweating instead of shivering.
The UK experienced a record-breaking winter heat after a SSW in February 2019, so the Met Office does not rule out the possibility of a similar swell in the coming weeks.
“Although the prolonged cold and snow events in February and March 2018 – which the British media called the ‘Beast from the East’ – were linked to a sudden excitement of the stratosphere, the record heat that took place in February 2019 , also followed by such an event, ”says meteorologist Matthew Lehnert.
We still have a long way to go before we can confidently promise what direction the weather will go in the wake of these polar changes.
But tools like this new algorithm will improve the chances of guessing, and it will continue, the more we learn more about our atmosphere.
“Despite these advances, there are still many questions about the mechanisms that cause these dramatic events, and how they can affect the surface. It is therefore an exciting and important area for future research,” says mathematician William Sevior of the University of Exeter.
This research was published in JGR atmosphere.