Dipole. It’s a word often used among meteorologists and climate scientists. But what does it mean?
In weather terms we can simply think of it as this: one side hot, one side cold. So, as a basic principle, it’s pretty direct. But in a world where extremes between hot and cold are becoming more intense, in North America which has just experienced its most extreme dipole anomaly since record keeping began in 1960, it’s also something that’s important to understand as it relates to ongoing human-caused climate change.
For a recent blockbuster scientific paper by Dr. Simon Wang and associates and published in Geophysical Research Letters has now linked this extreme temperature differential, related polar vortex collapse events, and the California drought with both ongoing physical changes to the Earth System due to human caused climate change and to the first rumblings of a monster El Nino in the Pacific.
Envisioning a Dipole Pushed into An Extreme Form by Climate Change
But to understand how an excessively extreme dipole relates to the historic events of the winter of 2013-2014, it helps to open up one’s imagination. It helps to describe the ground-breaking information provided by Dr. Wang’s new paper in descriptive terms. It helps to, at first, envision a wave. Then to imagine the up-slope of the wave forming a hot, red shape. Now imagine the down-slope forming a cold, blue shape. Now think of this wave growing more intense, extending further in both its up-slope and in its down-slope. Growing hotter on the up-slope side and comparatively colder on the down-slope side.
(GFS Model summary of Polar Vortex Collapse event on January 19, 2014 shows 850 mb temperatures over the Eastern US colder than the same temperatures over parts of Greenland and the Arctic Ocean. 850 mb temperatures over St. Augustine, FL are the same as 850 mb temperatures over central Greenland. Anomalies on the hot side of the dipole in the Arctic hit +40 degrees Fahrenheit in some places. Anomalies on the cold side of the dipole hit more than -35 degrees F in some places. Note the twin, dense high pressure systems sitting sentinel just off the California Coast and deflecting storms north into Alaska. Image source: NOAA/GFS.)
Having established the wave form and related temperature extremes, lay the shape over North America and adjacent Pacific Ocean. The up-slope covers the Eastern Pacific, Alaska, a section of the Beaufort Sea in the Arctic, Western Canada and the Western US. The down-slope swings from the eastern side of the Beaufort, on in through Central and Eastern Canada and bisects the US diagonally from the Dakotas to the Gulf Coast east of Texas.
Now let’s envision this wave as a flow of upper level air called the Jet Stream and let’s think about the various atmospheric aspects that feed it. Looking west, we happen upon a very warm pool of water in the Western Pacific east of the Philippines. This warm pool is the source of an El Nino that will likely occur within one years time. A heat pocket given added intensity by both rising atmospheric temperatures and strong winds transferring that added energy into the vast Pacific Ocean. The heat waits, wanting to spread out across the Pacific surface in an energetic return to the air. But, for now, it simmers in its deep pool, providing energy for the powerful dipole we’ve just described.
The heat from this warm pool radiates into the atmosphere creating lift. Further north, a cold pocket is driven south by another strong atmospheric wave pattern over the Asian continent. The cold air pocket runs south over Japan. The hot and the cold difference generates a very strong upper level synoptic (horizontal form weather patterns stretching more than 1,000 kilometers) wind pattern that stretches all the way across the Pacific Ocean.
The winds run southwest to northeast until they encounter the hot bulge of our already described dipole over the Eastern Pacific near the US west coast and Canada. This warm current turned the already rapid winds due north where they rushed up over Alaska and into a sea ice pack far weaker than in decades past. A sea ice sheet gradually thinning, breaking up, and venting heat from a warming Arctic Ocean below. And so these, already strong, winds were not turned back by the now much weaker cold until they had driven far, far into the Arctic Ocean (and it is here that we must give a hat tip to Dr. Jennifer Francis, who finds her predictions regarding sea ice loss and high amplitude Jet Stream waves again validated).
(Upper level wind pattern on January 23, 2014 shows a polar vortex that has essentially been ripped in half by the warm side of the west coast dipole and the high amplitude Jet Stream wave forming over top of it. Image source: University of Washington.)
Now imagine a strong dome of high pressure forming in the wake of this powerful and ongoing wind flow, sheltered and growing ever stronger on the hot side of the dipole. Imagine it blocking the path of storms, even as it concentrated heat and warmth. Imagine California receiving 1/4 or less of its typical winter rainfall as a result. A most recent and extreme insult to years of drought forcing authorities to ration water in many places.
Now return to that strong wind finally being turned south somewhere in the far, far north, in the Beaufort Sea just south of the North Pole. Then imagine these now cold-laden winds rushing south. Running over Hudson Bay and eastern Canada. Roaring over the Great Lakes and carrying with them a cyclone of cold Arctic air that should have remained in the far north. The polar vortex that should have stayed over places like Svalbard but instead collapsed under the warm wind flow and shifted far south to places like Toronto or Chicago or Detroit or Washington DC.
Now at last imagine another synoptic pattern as the Arctic air of the polar vortex encounters the warmth of the Gulf Stream. This pattern is laden with powerful storms that bomb out over the UK again and again, resulting in the stormiest winter for that island nation in over 200 years.
And here we have the dipole of the winter of 2013 and 2014. A west coast that was hot, hotter than usual all the way from California to the far north of Alaska and an East Coast that from Canada to the Gulf Coast became the repository for cold, cold Arctic air that was shoved south as the polar vortex collapsed down the steep face of the one of the largest and longest lasting Jet Stream waves on record.
(Dr. Francis explains how polar amplification results in higher amplitude Jet Stream wave patterns.)
Dipole. One side hot. One side cold. But, in this case, in the case of the winter of 2013-2014, it’s a historic and anomalous dipole. A freak born of the climate change we’ve caused mixing up with the Pacific Ocean heat of a rising El Nino. A record hot, dry winter for the US West that ignites wildfires in winter and forces the government to ration California water resources. A severe dry spell that closes farms and drives US food prices up by 15%. A record cold, stormy winter in the Eastern US and a series of super-intense storms screaming across the North Atlantic to submerge Somerset and rip massive chunks out of a rocky UK coastline.
This clear picture of a climate-change caused event was this week provided through the groundbreaking new research by Dr. Wang and fellows. These top scientists engaged climate models and analyzed past records to find the culprits of the weather extremes we witnessed during this past winter. And what they found was a very high correlation in the models with the extreme dipole over North America and the Arctic, an oncoming El Nino, and climate change driven impacts.
For not only was this year’s dipole the most extreme on record, it was also likely made far more extreme by an emerging Monster El Nino acting in concert with severe global-warming related reductions in Arctic sea ice cover, increases in Pacific Ocean heat and atmospheric moisture content, and related changes to the upper level air flows of the Northern Hemisphere polar Jet Stream.
Read Further Excellent Reporting on the Wang Report Here:
Large and Growing List of Scientific Studies Linking Human Climate Change to Current Weather Extremes (hat tip to Weather Underground)
(Partial list, view the rest here)