|Boston during the winter of 2015. Will a warming|
Arctic paradoxically give us more winters
like the one pictured?
As the Washington Post's Capital Weather Gang reported this week, we're going to have to talk about the polar vortex again, that weather system that became such an internet sensation a couple winters back.
The polar vortex is always up in the Arctic in the winter. It's a tightly wound circulation of frigid air that is perfectly normal, not the monster it was made out to be in the winter of 2013-14.
But a warming Arctic might be screwing around with that polar vortex.
Says the Washington Post:
"Occasionally (the polar vortex) fragments and pieces of it plunge into eastern North America, carrying bitter cold air. The winters of 2013-2014 and 2014-2015 witnessed several such polar vortex disintegrations and resulted in record setting cold snaps."
The polar vortex has showed a weakening trend over the past three decades, says the study in Nature Climate Change, making it easier to fragment and sent cold air into parts of Europe, Asia and North America, especially in the late winter and early spring.
Other studies have shown this overall polar vortex weakening, but the latest study takes things a little further. It's complicated, but an oversimplified version of it is this:
There's more open water in the Arctic in the autumn and early winter in recent years. That means more evaporation, and more water vapor in the air that falls as snow in Siberia and other high latitude locations.
The snow cover up there is thus, counterintuitively, more widespread than usual, which helps sets off weather pattern changes that make the polar vortex more likely to fall apart.
Additional complicated weather patterns favor fragments of the polar vortex to unload on eastern North America in late winter and early spring, mostly March, so we would be more prone to terrible cold snaps during that time of year, which prolongs winter.
Or at least give us weather whiplash. There have also been notable heat waves in recent years during March when the polar vortex isn't unloading on us. Remember the 80s in mid-March, 2012. And 70 degrees plus in early March last year?
The hints of spring might be prone to getting clobbered by these cold waves. Which screws ups and freezes early budding plants and fruit trees, causing crop losses, and less importantly, aggravated gardeners. It's a situation we saw last year, I know.
Of course, this doesn't always happen. A strong El Nino last year kept the Arctic air pretty much bottled up over the far north, and many of us in the Northeast enjoyed (or cursed) the warmest winter on record.
Even then, a brief very sharp cold wave around Valentine's Day brought some daily record low temperatures, and there was a temporary chill down in the second half of March and early April before the warmth returned. Which created the above mentioned havoc with frozen flowers on fruit trees.
As Scientific American notes, this is just another piece of evidence that global warming can cause more extremes in weather. Occasionally, those extremes are bitter cold, despite the overall warming trend.
This new study the Washington Post cites is not the final word, as there is controversy among scientists as to what Arctic thawing means, exactly how it affects the polar vortex, and howwe might feel the effects down here where we live.
We just know that things are getting screwed up with climate change, and we're only beginning to understand the picky details of how this will play out.
By the way, as I write this on a mild early November morning, there is much above snow cover in Eurasia, including Siberia, and much below normal Arctic sea ice, the Weather Channel notes.
Many forecasters are saying this will lead to a bitter winter this year. Starting as soon as just before Thanksgiving, according to some predictions.
Bundle up and stow cash for those high winter heating bills!