Jet stream crosses equator (hint: maybe not a good thing)

Here’s a bit from the Robert Scribbler blog mentioned in the story:

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.