Early polar vortex disruption: record-early Arctic shake-up draws scientists' attention
The Arctic polar vortex has weakened and split earlier in the season than meteorologists have seen before, raising questions about winter weather in North America and Europe.
An early polar vortex disruption is unfolding high above the Arctic, and climate scientists say its timing is unprecedented in modern observations. The polar vortex, a spinning mass of cold air over the North Pole, has weakened and shifted position in recent days, and forecasts suggest it could reverse direction by mid-November.
What is happening in the atmosphere
The polar vortex normally strengthens each autumn as Arctic temperatures fall. Strong westerly winds form in the stratosphere, roughly 10 to 30 miles above the surface, keeping the coldest air locked near the pole.
Disturbances in the atmosphere can warm the stratosphere, weakening those winds. This process, called a sudden stratospheric warming (SSW), can eventually cause the westerly winds to reverse into easterlies. The vortex has already stretched and briefly split into two smaller circulations.
If the winds keep weakening and reverse as forecast, the event would be classed as a major SSW. Scientists say such disruptions usually occur in mid-winter, which makes an event in early November stand out.
A record for the calendar
Jeff Knight, lead climate scientist at the UK Met Office, told the BBC that the event would appear to be the earliest on record across the 75 years of observations. Andrea Lopez Lang, an associate professor at the University of Wisconsin–Madison, described the disruption as happening at what may be the earliest point in the year on record.
Earlier sources cite November 28 in 1968 and 1969 as the previous earliest dates for a major SSW, depending on the report. The reports differ on this detail, so the exact prior record should be read with that caveat.
Judah Cohen, a climatologist at the Massachusetts Institute of Technology, said the event was exciting for weather watchers. "Everybody's hair is on fire in the climate or meteorologist community," he said.
Possible effects on winter weather
A vortex disruption can push cold air toward North America and Europe, and it can shift the jet stream into a blocked pattern that brings colder, northerly or easterly winds. It can also raise the chance of snow, especially in eastern parts of the UK.
Timing and location remain uncertain. Lopez Lang said the disruption looks likely, but "where everything sets up is still in question." Cohen noted that the event could turn out to be minor and be quickly forgotten, or major and be recorded as a landmark.
The UK Met Office had already pointed to a stormy start to winter, with a colder spell possible late in the season, in line with an El Niño pattern. Professor Andrew Charlton-Perez of the University of Reading said the typical response to an SSW is colder, drier conditions over Europe and the UK, but that the unusual timing makes a cold spell harder to predict now.
Why it is happening so early
Scientists have not confirmed the cause of the early timing. Knight said it could be part of normal variability, but suggested the current strong El Niño may have "helped load the dice" for this event, while adding that there is not yet enough evidence to say so. A link between strong El Niño years and early SSW events is unclear and will need further research.
What we know so far
The polar vortex has weakened, split and may reverse in the coming days, an event described by experts as unprecedented for this time of year. Its effect on winter weather in North America and Europe is still unclear. Forecasters say it is too early to know whether these changes will alter the winter outlook, and the picture is expected to become clearer as the vortex evolves.
Notes for editors: the BBC report cites a Met Office scientist; CT Insider and Scientific American reports were used for context. Neither the 1968 nor 1969 date has been independently verified in this article.
