Gillian, n all,
This is my story and I am sticking to it: Air rises in the intertropical convergence zone which roughly separates the northern hemisphere atmosphere from the southern. The air rising in this zone sheds its moisture and moves poleward, and is jerked rightward until it consists of a dry current moving West to East in the northern hemisphere, at about 30 degrees, the sub tropical jet. It’s moisture relieved, it is dry and so tends to sink. The return flow descends (and warms) forming the subtropical highs, the subtropical inversion, and eventually, a current of most air at the surface moving steadily south westward, the trade winds. This whole cycle is called a Hadley Cell. There are two more Hadley cells, one at around 30-50 degrees, and the other, the polar vortex. (Do not over dramatize the polar vortex; fill wash basin with warm water and a little suds, get it rotating in a counter clockwise direction as best you can, and then let it go by itself. There’s your polar vortex.) Between the polar vortex and the midlatitude Hadley cell, there is another Jetstream at 40-60 degrees N. which tends to seal off the arctic from mid latitudes to some degree. Jetstreams can be more or less sinuous and more or less synchronized. The poleward humps in a jet stream are called ridges and the equator-ward dips are called troughs. There is some sort of relation between the velocity of a jet stream and the amplitude of it’s troughs and ridges, but I am hazy on that. Because of their clockwise circulation, ridges tend to capture and foster high pressure areas; Because of their anti-clockwise circulation, troughs tend to capture and foster low pressure areas. The speed of jetsteams is governed by the temperature contrasts between Polar and equatorial regions. In the winter hemisphere, as you move poleward, days shorten and the sun angle becomes lower, each effect enhancing the other, and, therefore, pole-to-equator contrasts are enhanced, and jet stream velocities are increased; in the summer hemisphere, the effect of day length and sun-angle compensate for one another, air temperature contrasts are greatly reduced, and Jetstream speeds are reduced. Also, the ITCZ is constantly moving north and south, so that the summer hemisphere is squished by comparison with the northern and the structure of the Hadley cells is less clearly defined. Local effects take over. Also the two jet streams become “shorter”, since as they are moved northward they have less distance to complete their circle around the globe. There is apparently a natural rhythm for every diameter of travel so as the jetstreams move N and S. they become more or less chaotic as they approach natural rhythms for a given diameter. A line between warmer air to the south and colder air to the north tends to form under the polar and the southern Jet, called the Arctic Front and the Mid-latitude front, respectively. When the jets are synchronized and the amplitude is great, then cold air at the surface is allowed to plunge southward , beneath the warmer air aloft. And Bob’s Your Uncle, everybody starts talking about the polar vortex. Nick Nick Thompson <mailto:[email protected]> [email protected] <https://wordpress.clarku.edu/nthompson/> https://wordpress.clarku.edu/nthompson/ From: Friam <[email protected]> On Behalf Of David Eric Smith Sent: Tuesday, February 16, 2021 3:29 PM To: The Friday Morning Applied Complexity Coffee Group <[email protected]> Subject: Re: [FRIAM] Nothing to do with nick, do we have a formula 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 On Feb 16, 2021, at 1:58 PM, Gillian Densmore <[email protected] <mailto:[email protected]> > wrote: For how ass the weather is because of artic air? I am prepared for to see a lot of fur-fetched replies. We can Wolf down some facts, or just retriever it out as just how it is. - .... . -..-. . -. -.. -..-. .. ... -..-. .... . .-. . 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