Sudden Stratospheric Warming and Polar Amplification: How Climate Change Interacts With the Polar Vortex

Over the past few years, the term Polar Vortex has dominated the broadcast weather media — gaining recent notoriety due to increasingly extreme weather events associated with a number of disruptions to Arctic atmospheric circulation patterns. In short, this swirl of cold air over the furthest north regions is being intensely disrupted by warm air invasions — both at the surface and in the upper levels of the atmosphere. A subject that we’ll explore further as part of this analysis.

Take the recent extreme February warming at the North Pole in which temperatures there rose to above freezing even as a major cold snap slammed into Europe this week. We’ve seen such varied headlines as Yes the North Pole is Warmer than Europe Right Now and Arctic Warm Event Stuns Scientists.

When it’s warmer at the pole than in Europe, it’s a sign that the weather is clearly out of whack. Especially when temperatures in a region spanning tens of thousands of square miles over the Arctic rocket to between 40 and 63 degrees Fahrenheit above normal. Scientists are notably concerned. Dr. Michael Mann, one of the world’s foremost experts on climate change characterized the polar warming event as:

…an anomaly among anomalies. It is far enough outside the historical range that it is worrying — it is a suggestion that there are further surprises in store as we continue to poke the angry beast that is our climate.

But what’s driving all this? Dr. Mann gives us a bit of a hint by describing our climate as an angry beast that’s being poked.

(Polar Amplification writ large. The entire region of the Arctic above the 80 degree North Latitude line has been 8.64 degrees Celsius warmer than normal for all of 2018 thus far. This is an extraordinary departure for a region that plays a critical role in how the Earth’s climate system functions. Image source: DMI.)

Perhaps another way to say it is that it’s a warming atmosphere that’s prodding the Jet Stream to take a chunk out of the Polar Vortex.

How might this work?

First, surface warming in the Arctic caused by increased radiative forcing from rising greenhouse gas levels and by follow-on reductions of Arctic sea ice and snow result in less temperature difference between the Pole and the Equator. This surface warming translates into higher levels of the atmosphere through convection.

Temperature difference is what drives the upper level winds. So a lower difference in temperature causes these winds to slow. When the Jet Stream winds slow, they tend to meander — forming large ridges and deep troughs. The elongated ridges and troughs eventually break like waves — pushing against the circulation of the Polar Vortex.

(NOAA graphic shows how a weak jet stream results in changes in atmospheric circulation and increased disruption of the Polar Vortex.)

When this happens, the speed of the winds that make up the Polar Vortex slow down and sometimes reverse. This results in the collapse of the column of upper level air held aloft by the Vortex’s winds. When the air collapses, it compresses, causing the stratosphere to warm. This falling column of warm air then can end up acting like an atmospheric wedge — driving the Polar Vortex apart and causing it to split.

The split then tends to generate smaller funnels that capture polar air and pull it south. Beneath the funnels, it can be quite cold as Arctic air invades places like North America or the UK (as happened this week). But at the Pole, where the cold air should typically reside, it warms up enormously.

That’s how, under a regime of human-forced climate change, you can end up with periods where temperatures are warmer at the Pole than they are in Europe.

It’s worth noting that Polar Vortex collapse events did occur in the past. But not in such a way that generated the kinds of historically extreme Arctic temperatures we see today. The primary driver for the recently increased extremity of weather driven by Polar Vortex collapse events being human-caused climate change, Polar Amplification, and related influences on the Jet Stream.


Warm Arctic Winds Rip Polar Vortex in Half, Blast East Face of Greenland Ice Sheet

Last night, at around 9 PM Eastern Time, a broad region just south of the North Pole was undergoing an extraordinary warm-up. Temperatures along the 37 W Longitude line just 80 miles south of the pole had surged to 33 degrees Fahrenheit. A reading warmer than a region of central Michigan thousands of miles to the south but running over an area of sea ice more accustomed to -5 F or lower temperatures during the great dark of the December night.


(Knife of warm air drives above freezing temperatures to within 80 miles of the North Pole on December 1 of 2014. Image source: Earth Nullschool. Data Source: UCAR, OSCAR, NCEP.)

It was the much warmer than normal core of an intense and anomalous Arctic heat surge. One that blasted up over Svalbard and flooded into the high Arctic. Meeting with a similar but weaker air surge to the south, both surface and upper layers of the Arctic Ocean atmosphere hosted a joining of rivers of warm air.

This warm air double envelopment neatly sliced the polar vortex in twain. The remnant cold air cores at the Jet Stream level slipped down over both the Canadian Archipelago and Central Asia. Leaving open the lane for warm, maritime air to surge over the Arctic Ocean region.


(Jet Stream level atmospheric circulation shows polar vortex cut in two with one circulation over the Canadian Arctic Archipelago and the other over Yamal, Siberia — scene to the freakish methane blowholes earlier this year. Image source: Earth Nullschool. Data Source: UCAR, OSCAR, NCEP.)

It is a pattern of negative phase Arctic Oscillation (AO) — featuring a warming in the central Arctic which flushes the cold air out. But this ripping of the polar vortex in half is also related to polar amplification due to the human heat forcing. In which the high Arctic has warmed dramatically in comparison with the rest of the globe. So the heat anomalies we see now are much higher than they would otherwise be, with abnormal warmth remaining even into a positive phase of the AO (which we may see a bit more of, should El Nino finally emerge).

It’s a feature also related to a warming of the upper atmosphere at stratospheric levels. Such Sudden Stratospheric Warming (SSW) events can often be associated with the kind of polar vortex split we are seeing now. And, from recent observations, we find temperatures over the Arctic Stratosphere are now in record range.

According to weather blogger, Matthew Holliday:

Even though I wouldn’t categorize this as a *sudden* stratospheric event as of yet, the warming that has already occurred will likely have effects by middle December. In fact, the warming that has occurred is currently at record levels for this time of year.

Recent scientific studies have also indicated an increasing prevalence of SSW events as atmospheric carbon dioxide levels rise.

Extraordinary Arctic Warming

For much of November, readings in the Arctic as a whole have ranged from +1.5 to +2.5 degrees Celsius above the global average. A region featuring the highest global anomalies in a world that just saw its hottest ten months in the past 136 years, and probably its hottest ten months in many thousands of years. A region well known for its cold — but warming far faster than almost anywhere else.

Global anomaly Dec 1

(The Arctic hits an extraordinary early December +3.16 C positive anomaly on the first day of the month amidst a flood of warm air from the Atlantic and Pacific Oceans. Image source: The University of Maine. Data Source: Global Forecast System Model.)

Today, beset by this abnormal heat, overall Arctic departures hit 3.16 C above the already hotter than normal 1979 to 2000 average. Regions within this warm zone showed readings well above 36 F higher than average. A kind of winter Arctic heatwave. One that will keep worsening as the human heat forcing continues its terrible advance.

Near Freezing Temperatures Over Zachariae Glacier During Meteorological Winter

Much of the added heat expanded through the region between the North Pole and Greenland, wrapping in a surface circulation that has tended more and more to envelop the frozen isle, Baffin Bay and the accompanying Canadian Archipelago.


(Warm front off Atlantic Ocean featuring blow torch like wind flow over the Zahcariae Glacier collides with Greenland, pushes far into Arctic Ocean. Image source: Earth Nullschool. Data source: Data Source: UCAR, OSCAR, NCEP.)

This morning, some of that circulation and its entrapped warm air flow rode up over the East Coast of Greenland, surging over the ocean-facing cliffs of the Zachariae Glacier. Pushing temperatures to almost above freezing in a period where much deeper cold should be firmly established.

A great flood of abnormal winter warmth and moisture. The leading edge of a flow of ocean and atmospheric heat driven all too obviously by human warming.



James Hansen: If It’s Warm, Why is it So Damned Cold?

Earth Nullschool

University of Maine



Global Forecast System Model

National Climate Data Center

Changes in Northern Hemisphere Stratospheric Variability Under Increased CO2 Concentrations

Hat Tip to Wili

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