Posted by
David Eric Smith on
Feb 16, 2021; 9:29pm
URL: http://friam.383.s1.nabble.com/Nothing-to-do-with-nick-do-we-have-a-formula-tp7600785p7600792.html
Gillian,
I was told several years ago (2018) by a specialist in this area that these extreme southerly dips in the jet stream are a consequence of the weakening of the polar vortex on Earth. It happens I was in Korea at a time corresponding to the Winter Olympics in PyeongChang, and we were freezing our asses off under a cold spell similar to this one. It too was due to a very southerly dip in the jet stream. So it was timely for this scientist to talk on the subject, and I got to sit with him at lunch and ask more questions.
I have an impression the jet stream functions, at least during part of the year, a little like a wall between arctic air contained to the north of it, and temperate or equatorial air to the south side. So when it swings very far south, the domain of arctic air extends further south than it normally would, and since we don’t normally experience winter arctic air, it seems very cold. But apparently these more extreme north-south swings are due to weakening of the vortex — when it turns faster the jet stream has less severe excursions.
My impression, in looking at jet stream patterns after that, is that when we see these swings we tend to see them in three places around the world: the central-to-eastern US, Eastern Europe or very-west Asia, and then over the Korean Peninsula. I haven’t checked whether they are doing the same thing just now.
(The fact that the jet stream likes to make these polygonal shapes reminds me of the pictures of the hexagonal patch on the north (?) pole of Saturn, the boundary of which I think is a similar kind of formation (roughly). The presence of continents on Earth causes this to not be a pure fluid phenomenon as it would be on Saturn.)
The non-intuitive part of it is that the vortex weakens because the arctic is not as cold as it should be. So we feel more cold, but on a global average, we are less cold. A similar phenomenon becomes more intuitive during the summer, when northern Sweden is experiencing uncontrollable forest fires.
n.b. There may be things in what I said above that are wrong because I haven’t understood them or didn’t hear it all correctly. So do find somebody who does this for a living to ask.
Eric
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