Polar Vortex Weakens Toward Earliest Breakdown in 75 Years of Records
The Arctic polar vortex is weakening toward its earliest recorded breakdown, the Met Office says. Here is how a reversal works and what it could mean for winter.
The ring of winds circling the North Pole high above the Arctic is weakening fast enough that some forecasters expect it to reverse direction by mid-November, which would be the earliest breakdown of the polar vortex ever recorded. The previous record was set on Nov. 28, 1969, The Telegraph reported.
Jeff Knight, lead climate scientist at the UK Met Office, told the BBC it would appear to be the earliest on record over the 75 years that scientists have been observing the vortex. A breakdown of this kind can push cold Arctic air south into Europe and change where the jet stream runs for weeks.
How the polar vortex works
The polar vortex forms every year as the Arctic cools in autumn. It is a band of westerly winds about 10 to 30 miles above the ground, in the layer of the atmosphere called the stratosphere. It usually builds in late summer and is strongest in December and January. While it holds, it keeps cold air locked over the pole and supports a strong jet stream that carries milder air toward Europe.
Disturbances rising from the lower atmosphere can weaken the vortex. Forecasters have measured a large drop in wind speed this autumn, and some now predict a sudden stratospheric warming, or SSW. In an SSW the westerly winds quickly flip and blow from the east, which can displace the vortex, stretch it or split it apart.
Judah Cohen, a climatologist at the Massachusetts Institute of Technology, told Scientific American the event was a big one for weather watchers “because it’s so unprecedented.”
Why it is happening so early
Scientists have not pinned down the cause. One explanation points to the current El Niño, which is forecast to be the strongest on record. Met Office meteorologist Aidan McGivern said El Niño strengthens the waves in the jet stream in the lower atmosphere. Those waves can travel upward into the stratosphere and knock the circle of polar winds off balance.
McGivern said El Niño years raise the odds of an SSW, and an SSW in turn raises the chance of colder weather in the UK. Seasonal outlooks built around El Niño had pointed to a stormy start to winter followed by a colder, drier January. Because this SSW would arrive so unusually early, forecasters say it is hard to tell when any cold spell would start or whether Britain will get snow in November.
What it means for Europe this winter
The atmosphere is chaotic and the outcome is uncertain, said Andrew Charlton-Perez, a professor of meteorology at the University of Reading. He told The Telegraph that a reasonably large collapse would shape the weather for 30 to 40 days. He compared it with the Beast from the East in 2018, when cold continental air settled over the UK, but noted that the air over Europe is not that cold yet, so he does not expect it to be as severe.
Where the cold air would end up is still open. Jim Dale, a meteorologist and founder of British Weather Services, said Norway, Sweden, Denmark and Germany were the current favorite but called the location “just guesswork” for now.
An SSW tends to bring less rain, which worries water planners after a summer drought across much of Europe. Charlton-Perez said the UK needs 120 percent of average rainfall this winter to be out of drought by next summer.
Energy is the other concern. A cold spell would raise heating demand. The EU is entering winter with gas storage about 72.4 percent full, the lowest for this time of year since records began in 2011, and the Institute for Energy Economics and Financial Analysis warned that a cold snap would drain reserves faster.
A separate worry in the Atlantic
Scientists are also watching a patch of unusually cold water south of Greenland, nicknamed the “cold blob.” Some researchers fear the Atlantic Meridional Overturning Circulation, a system of currents that carries warm water north, is starting to weaken. A severe slowdown would bring harsher winters to Europe, though a full collapse would probably unfold over many decades. Britain is funding an early-warning system for it.
What happens next
Forecasters will watch whether the winds fully reverse by mid-November, as some expect. The Met Office is the official forecaster for the UK, and readers should follow its warnings and the advice of local authorities as conditions change.
Source: Yahoo
