Stratospheric Warming & A Failing Jet Stream - How The Polar Climate Is Disintegrating
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.
Link to tweet
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.
EDIT
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.
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(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.
EDIT
https://robertscribbler.com/2018/02/28/sudden-stratospheric-warming-and-polar-amplification-how-climate-change-interacts-with-the-polar-vortex/
= new reply since forum marked as read
When I started to fly airliner class aircraft in the early 1980s, the behavior of the jet streams was pretty consistent. The polar jets flowed roughly west to east, shifting south in the winter and back north in the summer
Over the years, these jets have become steadily more erratic. They typically undulate much more, often flowing north-south, then south-north and even curling to east west in spots. In more recent years, they have even broken up at times and not even been there.
This is the current NAM loop at 300millibars:
What you are seeing is the polar and subtropical jets actually merging and then splitting apart again. That did not happen-ever-when I started flying. Today, this is considered normal behavior. Although this isn’t a big problem for flying, it is a huge problem for a consistently cold arctic. It won’t be fixable in my lifetime.
