Hemisphere Jet Stream crosses the Equator in this Earth
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.)
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.
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.
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
Climate Change-Driven Loss of Seasonal Integrity?
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.
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.
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.
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
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.