Stu Ostro's Meteorology Blog

Polar Vortex, Global Warming, and Cold Weather

By: stuostro, 11:47 AM GMT on January 10, 2014

Image credit: Skreened



I just searched for "polar vortex" and got about 17,000,000 results.  Apparently the number doesn't display when specifying a date range; I wonder how many would have come up if I had searched a week ago!  And searching for "polar vortex" "global warming" gives 78,300,000.

Looking at those topics in relation to the recent cold weather over parts of the U.S. and Canada from an objective, scientific perspective ...


POLAR VORTEX



Image credit: NOAA/CPC

  • A polar vortex is not only not something new or mysterious, it's a standard feature of the atmosphere, strongest in winter.  The term has been used in the scientific literature at least back as far as 1939 in a paper by Rossby. [Update: I don't know if it was in a scientific journal back this far, but the term was used at least as early as 1853. (H/T to the commenter below.)]  This meteorological phenomenon has likely been present for as long as there has been weather on Earth.  
  • A polar vortex is large circulation in the upper atmosphere that has generally west-to-east winds circling the Earth.  It's not a cold wave or a storm.  As the name implies, polar vortexes (or vortices -- either is grammatically correct) are usually centered in the polar regions, one near the North Pole and another near the South Pole. 
  • Polar vortexes exist at a high altitude.  They are most well-defined in the stratosphere, higher up than the portion of the atmosphere in which most of what is typically thought of as weather is (troposphere).  Their circulations extend down to lower altitudes (the atmosphere is a continuum) but are more irregular and chaotic in the troposphere.  As observations and understanding of higher altitudes have evolved, the American Meteorological Society Glossary definition has evolvedoriginally referring to the middle and upper troposphere (which is where I originally learned it was), and then the middle troposphere to the stratosphere, and the now the scientific literature mostly refers to the stratospheric polar vortex.  NASA Goddard refers to it extending from the tropopause (boundary between troposphere and stratosphere) all the way up to the mesosphere, which begins approximately 50 kilometers (~31 miles) above the Earth's surface, and indeed the current chart above of the *1* millibar height shows the polar vortex very pronounced at almost that altitude!    [Update: The AMS has again changed the definition.  There's what seems to be an a typo at that link: "not merely a stratospheric phenomenon" must mean "not merely a tropospheric phenomenon," since it's referring directly to the original Glossary entry that cited only the troposphere. They still refer to two "centers" when they're really axes or lobes, and only in the long-term means, which can be misleading, as they're not necessarily there at any given time (and much of the time are not).  And it says the vortex is strongest during the winter in the upper troposphere and stratosphere, whereas what started all the "endless media mangling" was the L in on the chart below at 500 mb in the mid troposphere.  And about that troposphere ... interestingly there are apparently many more uses of "circumpolar vortex" in the literature in regard to that level than just "polar vortex" ... which makes sense, since while a subtle semantic difference, the definition of circum- seems to apply well to the tropospheric manifestation, given that there it's largely a band of westerlies circulating around, but removed from, the pole, and relatively irregular and chaotic, stretching (figuratively and literally) the term "vortex," whereas the stratospheric polar vortex is more truly polar and more truly a vortex.]
  • Its air flow spins around like a large wheel.  There are "waves" which rotate around like spokes in a wheel. Sometimes (in the Northern Hemisphere, rarely in the Southern) the wheel breaks into separate smaller wheels displaced farther from the Pole, and around the smaller wheels some of the air flows from east to west.
  • The recent arctic blast might have had a connection to the stratospheric polar vortex, but's that's tenuous at best. At lower altitudes, there was a sharp dip in the jet stream ("trough") over Canada and the U.S. that could be considered a portion of the tropospheric polar vortex circulation, but such a trough is not uncommon; this one was just particularly strong.  And on the first map below, from Monday evening at the peak of the cold, while what I've circled over Ontario is what caused all the hype and hysteria, is that the polar vortex? What about all the other things I've circled?  Or is the polar vortex the large circle/circulation within which the others are?  What about the circulations outside that which broke off from the main polar jet stream?  Well, on the second map, of the stratosphere (squarely in it at 30 mb, a bit lower than the 1 mb map above), you sure can see what/where the stratospheric polar vortex is!  Lines on the map represent the air flowing counterclockwise in the direction of the lines with the center of the vortex over the North Pole. And on the third map, three days later, even though the frigid arctic air had retreated and there had been a big warm-up the circulation is nearly the same and still extending southward well into the Lower 48, in fact if anything slightly farther!  Further illustrating the problem with the polar vortex meme!  (At that level by then there had been an elongation of the core and a couple of centers show up.  A bit lower, at 70 mb, that is more apparent; higher at 10 mb, not so much.  There has been some stratospheric warming that this might be related to, but only a modest amount, and the vortex has not completely split like at other times such as last January, when one of my images of the year was of that vortex split, and this is occurring as the temperatures on the Earth's surface in the U.S. and into southern Canada are getting a lot warmer, not colder. And ironically, there was more of a collocation of the vortex in the stratosphere & troposphere and very cold air at the Earth's surface on New Year's Day, but it didn't sweep across the U.S. because the other factors that ensued a few days later were not present.) 
  • There was that system dropping south from the Arctic and one from the Pacific which combined to bring cold air down from Canada.  That sort of thing happens frequently; this arctic plunge was just colder than usual.
  • The recent cold wave was not unprecedented, and 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). The intensity of this cold has been relatively rare in the past couple decades, however.   Temperatures during this cold wave were not nearly as cold as they can get on Mars, which is approximately -225°F.


500 MB  MONDAY EVENING JANUARY 6

Image credit: Colorado State University


30 MB  MONDAY EVENING JANUARY 6



30 MB  THURSDAY EVENING  JANUARY 9 

Image credit: NOAA/CPC


GLOBAL WARMING


  • Global warming did not create polar vortexes, though the changing climate might be changing the nature of them.  Nor did humans create the term this week: as noted above, it's been an accepted scientific one for at least 75 years

  • Cold weather at a particular place/time does not disprove global warming -- it does not negate the decades of temperature rise in the graph below.  Global warming and a cold wave are not mutually exclusive




Image credit: NASA GISS

  • 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 there has been amidst a large area of warmer-than-average temperatures.  In the Southern Hemisphere, heat which has been extreme and more climatologically significant than the cold has occurred in places such as Australia and Argentina.  


Image credit: NOAA/ESRL

 

Winter Weather Climate Change

Updated: 3:53 AM GMT on February 25, 2014

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About stuostro

Senior meteorologist at The Weather Channel. Proud to be a weather-obsessed weather geek. Would be a DJ if not a meteorologist.

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