A Displaced Polar Vortex and Its Causes

By WUWT Regular “Just The Facts”

If you aren’t familiar with Stratospheric Polar Vortexes, you can get acquainted here, here and here.

“A strong link exists between stratospheric variability and anomalous weather patterns at the earth’s surface. Specifically, during extreme variability of the Arctic polar vortex termed a “weak vortex event,” anomalies can descend from the upper stratosphere to the surface on time scales of weeks. Subsequently the outbreak of cold-air events have been noted in high northern latitudes, as well as a quadrupole pattern in surface temperature over the Atlantic and western European sectors, but it is currently not understood why certain events descend to the surface while others do not. This study compares a new classification technique of weak vortex events, based on the distribution of potential vorticity, with that of an existing technique and demonstrates that the subdivision of such events into vortex displacements and vortex splits has important implications for tropospheric weather patterns on weekly to monthly time scales. Using reanalysis data it is found that vortex splitting events are correlated with surface weather and lead to positive temperature anomalies over eastern North America of more than 1.5 K, and negative anomalies over Eurasia of up to −3 K. Associated with this is an increase in high-latitude blocking in both the Atlantic and Pacific sectors and a decrease in European blocking. The corresponding signals are weaker during displacement events, although ultimately they are shown to be related to cold-air outbreaks over North America. Because of the importance of stratosphere–troposphere coupling for seasonal climate predictability, identifying the type of stratospheric variability in order to capture the correct surface response will be necessary.” Mitchell et al. 2012 – Paywalled

During January 2014 the Northern Stratospheric Polar Vortex appears to have experienced a weak vortex event and displacement, i.e. here is a 10 hPa/mb – Approximately 31,000 meters (101,700 feet) Height Analysis showing the low pressure area of the Stratospheric Polar Vortex being displaced (squeezed) on January 7th;

and this Northern Hemisphere Temperature Analysis at 10 hPa/mb shows the Northern Stratospheric Polar Vortex apparently with two lobes on January 11th, 2014:

Northern Polar Wind at 10 hPa/mb also shows the Stratospheric Polar Vortex still displaced at present (if you click on the picture it will link to an animated version):

and when Polar Wind is overlaid with Temperature, you can clearly see the cold “air from very high altitudes” that descends “through the center of the vortex, moving air to lower altitudes over several months,” “NASA” (Click the pic to animate):

“Large regions in northern Asia, Europe and North America have been found to cool during the mature and late stages of weak vortex events in the stratosphere. A substantial part of the temperature changes are associated with changes in the Northern Annular Mode (NAM) and North Atlantic Oscillation (NAO) pressure patterns in the troposphere. The apparent coupling between the stratosphere and the troposphere may be of relevance for weather forecasting, but only if the temporal and spatial nature of the coupling is known. Using 51 winters of reanalysis data, we show that the development of the lower-tropospheric temperature relative to stratospheric weak polar vortex events goes through a series of well-defined stages, including the formation of geographically distinct cold air outbreaks. At the inception of weak vortex events, a precursor signal in the form of a strong high-pressure anomaly over north west Eurasia is associated with long-lived and robust cold anomalies over Asia and Europe. A few weeks later, near the mature stage of the weak vortex events, a shorter-lived cold anomaly emerges off the east coast of North America. The probability of cold air outbreaks increases by more than 50% in one or more of these regions during all phases of the weak vortex events. This shows that the stratospheric polar vortex contains information that can be used to enhance forecasts of cold air outbreaks. As large changes in the frequency of extremes are involved, this process is important for the medium-range and seasonal prediction of extreme cold winter days.” Kolstad et al. 2010

Here is Northern Hemisphere – Vertical Cross Section of Geopotential Height Anomalies and the Northern Annular Mode (NAM) or Arctic Oscillation (AO) Index, which shows large positive Height Anomalies and the AO swinging negative in January:

And here is North Atlantic Oscillation (NAO) Index for the prior 4 Months, showing a positive swing in mid-January:

So what caused the weak vortex event, displacement of the Northern Stratospheric Polar Vortex and cold air outbreaks?

There are several potential factors:

“A vortex displacement event is associated with anomalously high wavenumber-1 planetary wave activity entering the stratosphere and is characterized by a vortex with a comma-like shape that is shifting equatorward. Often this shifting occurs ‘‘top down’’ and the vortex has a baroclinic structure. Subsequently the Aleutian high, a weak anti- cyclone, encroaches over the pole and is especially dominant at lower levels.”

“A vortex splitting event is associated with anomalously high wavenumber-2 planetary wave activity entering the stratosphere. During such an event the vortex barotropically splits into two ‘‘daughter’’ vortices that tend to align along the 90°E – 90°W axis, with one centered over Siberia and the other centered over northeastern Canada (Matthewman et al. 2009, hereafter M09).”

“Analyses show that the most extreme vortex variability occurs most commonly in late January and early February, consistent with when most planetary wave driving from the troposphere is observed. Composites around sudden stratospheric warming (SSW) events reveal that the moment diagnostics evolve in statistically different ways between vortex splitting events and vortex displacement events, in contrast to the traditional diagnostics.” Mitchell et al. 2011

Planetary Wave 1 activity can be see on this Zonal Wave #1 Amplitude Jan, Feb, March Time Series;

and Planetary Wave 2 on this Zonal Wave #2 Amplitude Jan, Feb, March Time Series:

There was some Planetary Wave 2 activity in early January, however there was strong Planetary Wave 1 activity throughout much of the month.

A second likely factor in the weakening and displacement of the Polar Vortex is Eddy Heat, i.e. “strong negative fluxes indicate poleward flux of heat via eddies. Multiple strong poleward episodes will result in a smaller polar vortex, Sudden Stratospheric Warmings and an earlier transition from winter to summer circulations. Relatively small flux amplitudes will result in a more stable polar vortex and will extend the winter circulation well into the Spring.” NOAA

Here you can see that 10 day Averaged Eddy Heat Flux Towards The North Pole At 100mb neared a record daily maximum in early January:

A third potential factor in Polar Vortex behavior is that “geomagnetic activity (used as a measure of solar wind parameters)” plays a role in the “variability of large-scale climate patterns and on changes in the global temperature.”, i.e.: “We have found positive statistically significant correlations between global temperature and the distribution of surface temperature over Eurasia, the East and Equatorial Pacific and over the North Atlantic for the period 1966-2009 correspond to large-scale climate patterns defined by climate indices. We found very similar positive correlations between geomagnetic activity and the distribution of surface temperature in the mentioned regions. As an effect of geomagnetic storms, energetic particles penetrate from the magnetosphere into the region of the stratospheric polar vortex. The increase of temperature and pressure can be observed over northern Canada. The vortex shifts towards Europe, rotates counter-clockwise and the wind blows from the polar region over Greenland southwards. It diverts the warm flow proceeding northward over the Atlantic, eastward along the deep Icelandic low extending as far as the Barents Sea and takes part in warming Eurasia. The strengthened zonal flow from Siberia cools the western Pacific with the impact on the warming of the equatorial and eastern Pacific when also a distinct 1976-78 climate shift occurred. Processes in the Atlantic and Pacific play a significant role and a time delay (wind forcing over the previous 1-4 yr) appears to be the most important for the relocation of the oceanic gyres. Results showing statistically significant relations between time series for geomagnetic activity, for the sum of climate indices and for the global temperature help to verify findings concerning the chain of processes from the magnetosphere to the troposphere.” Studia Geophysica & Geodaetica, Bucha 2012

A Coronal Mass Ejection (CME); hit Earth around January 1st:

Ensemble WSA-ENLIL+Cone Model Evolution Movie for Median CME Input Parameters – Dynamic Pressure:

and the Magnetosphere was rocking and rolling:

However, potential influences of Solar activity on Polar Vorticity are speculative and in the past Leif Svalgaard has challenged the potential that Solar influences on the upper atmosphere could influence Earth’s climate.

Finally, we have the Wobbly Jet Steam hypothesis put forth by Jennifer Francis, of Rutgers University and other, i.e.:

“The Arctic is heating faster than the rest of the world, hurried along by the disappearance of polar sea ice. Bright white ice reflects energy back into space; dark blue water absorbs it. Arctic temperatures are about 2 degrees Celsius warmer there than they were in the mid-1960s. (The average temperature increase for the Earth’s atmosphere overall is about 0.7 degree C, since 1900.)

In other words, the temperature difference between the Arctic and North America is shrinking. That’s one factor causing wobbliness in the jet stream, the west-east current that circles the Northern Hemisphere, according to Jennifer Francis, research professor at Rutgers University. Normally, that river of air keeps low-pressure cold air contained above the Arctic and holds higher-pressure warm air above the temperate regions, where most people live.

Scientists tend to call the jet stream a “polar vortex,” Francis says.

A slowing in the jet stream has caused it to zigzag, carrying warmer temperatures farther north than usual—and Arctic cold farther south. “The real story,” Francis says, is that the jet stream is “taking these big swings north and south and that’s causing unusual weather to occur in a number of places around the Northern Hemisphere.” Bloomberg Businessweek

I am not sure which scientists beyond Jennifer Francis “tend to call the jet stream a ‘polar vortex,'” as these are two distinct and separate climatic phenomena, i.e.:

“The jet stream consists of ribbons of very strong winds which move weather systems around the globe. Jet streams are found 9-16 km above the surface of the Earth, just below the tropopause, and can reach speeds of 200 mph.” Met Office  Whereas “the polar vortex extends from the tropopause (the dividing line between the stratosphere and troposphere) through the stratosphere and into the mesosphere (above 50 km). Low values of ozone and cold temperatures are associated with the air inside the vortex.” NASA

This graphic is helpful in seeing the height and location of the Polar Jet, one of the Jet Streams in relation to the Tropopause, down to which the Stratospheric Polar Vortex can extend:

Additionally, in the following image the Stratospheric Polar Vortex is delineated by the “Arctic Front”, whereas the Jet Stream is delineated by the “Polar Front”:

Jennifer Francis’ comment that “Scientist tend to call the jet stream a ‘polar vortex'” reminds me of this graphic:

But I digress, there are two key weaknesses in the Wobbly Jet Steam hypothesis.  Firstly, there does not appear to be a correlation between Sea Ice Area and Extent and the Cold Air Outbreaks. Secondly, it seems highly suspect that the extent of Arctic Sea Ice in September and October could have a significant impact on Stratospheric Polar Vortex behavior in January.

From a correlation perspective, the prior most notable Polar Vortex associated Cold Air Outbreak was the January 1985 Arctic Outbreak:

“The January 1985 Arctic outbreak was the result of the shifting of the polar vortex further south than is normally seen. Blocked from its normal movement, polar air from the north pushed into nearly every section of the eastern half of the United States, shattering record lows in a number of states. The effects of the outbreak were damaging. At least 126 deaths were blamed on the cold snap and 90 percent of the citrus crop in Florida was destroyed in what the state called the “Freeze of the Century.” Florida’s citrus industry suffered $1.2 billion in losses ($2.3 billion in 2009 dollars) as a result of the inclement weather. The public inauguration of President Ronald Reagan for his second term was held in the Capitol Rotunda instead of outside due to the cold weather, canceling the inaugural parade in the process. (Because Inauguration Day fell on a Sunday, Reagan took a private oath on January 20 and the semi-public oath on January 21.)” NOAA

(An interesting aside, on January 12, 2014 “KinkyLipids” changed the Wikipedia January 1985 Arctic Outbreak page from ‘Arctic outbreak’ to ‘cold wave’, ‘Janaury’ to ‘Winter’ and “moved page Winter 1985 Arctic outbreak to Winter 1985 cold wave” because “Sources do not use the term ‘Arctic outbreak’. The term ‘cold wave’ matches other Wikipedia articles”. Not sure why one wouldn’t call “the outbreak of cold-air events” an “outbreak”, but you can visit the new Wikipedia “Winter 1985 cold wave” at the old January 1985 Arctic Outbreak link http://en.wikipedia.org/wiki/January_1985_Arctic_outbreak)

Regardless of what it’s called, the January 1985 Cold Air Outbreak occurred during a time of slightly above average Northern Sea Ice Area, where the January 2014 Cold Air Outbreak occurred during a time of slightly below average Northern Hemisphere Sea Ice Area:

Also, Arctic Sea Ice Extent was within two standard deviations of the 1981 – 2010 average for the entirety of 2013:

and there was signifacantly more Sea Ice Area prior to the recent the strong Cold Air Outbreaks occurred, versus 2012 when the Cold Air Outbreaks weren’t as strong:

Aside from the apparent lack of correlation between Cold Air Outbreaks and Arctic Sea Area and Extend, there is another aspect of Arctic Sea Ice that makes the Wobbly Jet Stream hypothesis even wobblier. The Arctic is mostly land locked and freezes over quickly in the Fall. Thus by December Sea Ice Extent has reached across much of the Arctic:

For the Wobbly Jet Stream hypothesis to be correct, either the approximately 1 Million Sq. km Sea Ice Area Anomaly in September and October must have a long lasting residual effect that lingers into January to disrupt the vortex, or the approximately 500K Sq km anomalies in November and December around the periphery of the Arctic are what must weakened and displaces the Stratospheric Polar Vortex.

Even Kevin Trenberth thinks the melting sea ice, warming Arctic, Wobbly Jet Steam causes cold January weather hypothesis is weak, i.e. “So with regards to the Arctic, there are certainly major changes in the Arctic Sea Ice. And those are biggest in the fall. We’ve had record low Arctic Sea Ice, about 40% decline in Arctic Sea Ice overall, since the 1970’s, in September. But the Arctic fills up in the winter time.” “And so at those times of years the Arctic Sea Ice it seems to me plays a much lesser role. The area affected is a lot less, simply because the arctic is land locked.”

So Planetary Waves, Eddy Heat, Geomagnetic Storms or Sea Ice, what do you think caused the weakening and displacement the Northern Stratospheric Polar Vortex in January 2014?

For an array of real time Northern Stratospheric Polar Vortex graphs and graphics please visit the WUWT Northern Polar Vortex Reference Page.