Is a polar vortex to blame for the recent blasts of frigid weather throughout the Upper Midwest and Northeast?
Headlines throughout the media and Internet this week were enough to send chills through most: “Polar Vortex on Its Way to Colorado,” “Polar Vortex: Great Lakes Almost Fully Frozen,” “Polar Vortex to Once Again Grip Midwest, Northeast,” and “Did Someone Order Another Polar Vortex.” What’s the real story regarding polar vortexes?
First of all, there’s nothing new or unusual about a polar vortex. The term has been around since 1853, and was first used in the scientific literature in 1939. One of several semi-permanent weather systems over the Earth, a polar vortex is a very broad, cyclonic circulation of winds that occurs in the upper atmosphere, generally centered over both poles (North Pole and South Pole). Both hemispheres have a polar vortex, which forms in late fall and generally reaches peak intensity in mid-winter. Polar vortexes occur at high altitudes, being most well-defined in the stratosphere, and occur higher up in the atmosphere than where most weather occurs in the troposphere. Polar vortexes are influenced mainly by wind movement and transfer of heat. In the fall, circumpolar winds begin to increase, causing the polar vortex to spin up higher into the stratosphere. In winter, the winds around both poles decrease, causing the air in the vortex to slow and the vortex to quit growing in size. Then, in late winter to early spring, heat and circulation return, causing the vortex to shrink in size. It is during this final stage that fragmentation of the vortex occurs, causing pieces of the polar vortex to be drawn into the lower latitudes. This breakup of the polar vortex generally occurs sometime between mid-March to mid-May, and signifies the transition from winter to spring.
In the case of the January arctic outbreaks, “…a large piece of the vortex broke off and was forced well to the south over Ontario and the northern Great Lakes. Contributing to this southward buckling of the jet stream was a pronounced northward diversion of the polar jet stream over the eastern Pacific Ocean and West Coast of the U.S. To the east, or downstream of this northward diversion or ridge of high pressure aloft, the polar vortex was forced southward.” So “…instead of cold, Canadian air grazing the northern tier of the U.S., then draining off into the north Atlantic Ocean, the heart of this Arctic air plunged south into the U.S.” Freezing temperatures were felt as far south as south Florida.
While the repeated cold waves we’ve been experiencing this year are record-setting, they’re not unusual or unprecedented, according to The Weather Channel’s Senior Meteorologist Stu Ostro. “There have been others in the past which have been of greater magnitude in a number of ways (such as in 1996, 1994, 1985, 1983, 1977, and farther back in time, perhaps the most extreme one on record, 1899),” says Ostro. What is noticeable, however, is the intensity of the cold, which Ostro says, “has been relatively rare in the past couple decades.”
Ostro also points out that “This recent cold weather must also be viewed in geographical context. While there have been frigid arctic air masses and major snow/ice storms the past few weeks in the Lower 48 and Canada, the area of below average temperatures is amidst a large area of warmer-than-average temperatures.” He points out, for example, that in the Southern Hemisphere, especially in Australia and Argentina, the extreme heat has been more climatologically significant than the cold that has been occurring in the Northern Hemisphere.
So what about global warming—has it produced stronger polar vortexes? “Global warming did not create polar vortexes, though the changing climate might be changing the nature of them.” He also adds that “There is increasing evidence that the additional warmth in the atmosphere is leading to a change in nature of weather extremes, possibly including patterns such as ones associated with recent weather in the U.S. and elsewhere.” Case in point, just this week the Agence France-Presse reported that 21,341 birds were killed in France by violent winter storms, something that hasn’t occurred since 1900.
March may be “coming in like a lion” for many parts of the U.S. and the world, but we need to look at the bigger picture for perspective. Climate change may be influencing the nature of polar vortexes, but polar vortexes don’t “cause” Arctic blasts. The atmosphere is much more complicated than that. Maybe the question we need to be asking is how much more extreme can these weather events get? Based on records taken from ice core samples, today’s “extremes” pale in comparison with those of the past. Perhaps we’re just beginning to see the tip of the iceberg.
Link to Article on Network: http://www.gcnlive.com/CMS/index.php/component/k2/356-polar-vortexes
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