Every winter in the northern hemisphere, a cold wind surrounds the North Pole like water around a drain. This is an annual weather pattern that meteorologists keep an anxious eye on: any significant change could suggest that Europe is cold. Right now, this wind is tearing in two.
Researchers at the universities of Bristol, Exeter and Bath have found a new way to predict the effects of several changes in this important airflow at the height of the stratosphere, at 10 to 50 kilometers (6 to 30 miles). .
Ironically, the cause of this cooling is a sudden burst of heat that drains into currents that spin through a window for only 24 to 48 hours.
With its temperature rising to 40 degrees Celsius, the vortex undergoes some rapid changes, changing course or breaking drastically into daughter vortices that sink against the surrounding atmosphere.
The results can be devastating. Just a few years ago, a sudden stratospheric warming (SSW) propelled Siberian cold air into Europe, delivering a high-pressure snow-laden cell that the media called The Beast from the East.
Focused on Scandinavia, the shock of the icy climate drove the ice westward to the UK, contributing to the transport of chaos and even several deaths.
That said, not all changes in this polar vortex end up in freezing conditions. Two years ago, the warming of stratospheric polar winds preceded one of the warmest winter days in UK recorded history.
Knowing which deviations are the presence of winter fury and which will be destroyed, will help a lot in making the weather forecast more accurate.
Surprisingly, these stratospheric warming events in themselves are not exactly rare, with records suggesting that an average of about a dozen of them occur at the Arctic polar vortex every decade.
“While an extreme cold weather event is not a certainty, about two-thirds of SSWs have a significant impact on surface climate,” says Richard Hall, a University of Bristol meteorologist and lead author of the new study.
Observations dating back more than six decades have provided researchers with 40 examples of such hesitations and splits in the northern stratospheric polar vortex, which report a tracking algorithm that attempts to predict the impact that each type of change will have in the meteorological systems of the northern hemisphere. .
The results suggest that each time the polar vortex splits into two smaller winds, we can expect more severe cooling events, compared to other SSW abnormalities.
It is an opportune result, with changes in the forecast of the air currents that appear during the weekend.
“As predicted, atmospheric observations now show that the Arctic stratosphere is experiencing a sudden warming associated with a weakening stratospheric polar vortex,” says Adam Scaife, head of long-range prediction at the Met UK office.
In addition, the change has all the hallmarks of the most dangerous type of SSW, meaning there are many chances that the predicted temperature drop is significant.
Having informed climate models certainly helps to improve the chances of knowing what to expect. But while modeling at this scale benefits from improved algorithms, there is still room for great uncertainty when it comes to clarifying the precise details in the coming days.
Interestingly, it could even turn out that Europe is sweating instead of chills.
After all, the UK experienced a record winter heat after an SSW in February 2019, so Met Office does not rule out the possibility of a similar blower in the coming weeks.
Although the prolonged periods of snow and cold periods in February and March 2018, dubbed by the British media as the ‘Beast of the East’, were related to a sudden stratospheric warming, the record warm period that is produced in February 2019 also followed event, “says meteorologist Matthew Lehnert.
We have a long way to go before confidently promising the path that the weather will take as a result of these polar changes.
But tools like this new algorithm will improve the chances of guessing and will continue to do so as we learn more about our atmosphere.
“Despite this progress, many questions remain about the mechanisms that cause these dramatic events and how they can influence the surface, so this is an exciting and important area for future research,” says University mathematician William Seviour. of Exeter.
This research was published in JGR Atmospheres.