It’s as if global warming were ringing the Earth’s atmosphere like some great, cacophonous alarm bell. The upper level zonal winds are swinging wildly from record high positive anomalies to record low negative anomalies. Gravity waves — the kinds of big atmospheric waves that tend to move air from the Tropics all the way to the Poles and are powerful enough to cause the Caribbean Sea to ‘whistle’ in the satellite monitors — are growing larger. And the Jet Stream now has redefined all boundaries — flowing at times from the East Siberian Sea in the Arctic across the Equator and all the way south to West Antarctica.
(Northern Hemisphere Jet Stream crosses the Equator in this Earth Nullschool screen capture to merge with the Southern Hemisphere Jet Stream. It’s the very picture of weather weirding due to climate change. Something that would absolutely not happen in a normal world. Something, that if it continues, basically threatens seasonal integrity.)
The big trough today begins near the Northern Hemisphere Pole. It pulls Arctic air down over Eastern Siberia and into a Pacific Ocean storm track. There, a second big dip in the Jet Stream pulls a crazy loop of this upper air flow further south. And here is where things get really weird — for the upper level river of air that began in the Arctic then makes a jump directly across the Equator.
But our story of a wayward Jet Stream doesn’t end there. The upper level air flow that originated near the North Pole joins with a building Southern Hemisphere Jet Stream ridge pattern over the Southeast Pacific. Feeding into very strong upper level winds, it turns southward into a high amplitude wave that crosses the Horn of South America and slams itself, carrying with it a big pulse of extreme warmth, into the upper level airs over Western Antarctica.
(An injection of hot, Summer air from the Northern Hemisphere into Southern Hemisphere Winter appears to have aided in the generation of 8 C above average temperatures over Western Antarctica during June of 2016. Image source: NOAA ESRL.)
A Climate Change-Driven Loss of Seasonal Integrity?
Like many extreme events resulting from human-forced climate change — this co-mingling of upper level airs from one Hemisphere with another is pretty fracking strange. Historically, the Tropics — which produce the tallest and thickest air mass in the world — have served as a mostly impenetrable barrier to upper level winds moving from one Hemisphere to another. But as the Poles have warmed due to human-forced climate change, the Hemispherical Jet Streams have moved out of the Middle Latitudes more and more. More and more it has invaded regions both within the Polar zone and within the Tropics. Now, it appears that the old dividing lines are so weak that flows of upper level air between Hemispheres can be exchanged.
That’s bad news for seasonality. Prevention of mixing of air between Hemispheres by the thick, hot tropical air mass is what has generated a strong division between Summer and Winter during the Holocene Climate Epoch. However, erode that boundary and you get more Summer heat spilling over into the Winter zone and vice versa. You get this weather-destabilizing and extreme weather generating mixing of seasons that is all part of a very difficult to deal with ‘Death of Winter’ type scenario.
In the very recent past, scientists favored a view that such mixing between Hemispheres was not possible. But recent observations of zonal wind patterns in the Tropics have shown that the zonal winds are now starting to enter periods when they move in concert even as much more powerful than usual atmospheric wave generating patterns are starting to emerge. The result appears to be really enormous gravity waves that transfer heat from Equator to Pole even as cross Equator upper level air flows are enabled.
(Upper level Equatorial zonal winds moved from record positive anomalies to record negative anomalies within a mere three month timeframe. Extreme variations in these wind patterns can generate very strong gravity waves and result in an increased Equator to Pole propagation of upper air flows. Image source: Sam Lillo.)
All these observations combined point to a very serious concern that Polar warming is flattening the atmospheric slope from Equator to Pole to such an extent that an increasing violation of the Hemisphere to Hemisphere seasonal dividing line may be a new climate change related trend. And that’s a kind of weather weirding that we are not at all really prepared to deal with.