I write at a time when the June temperature record has been broken three days in succession in the UK, and the reasons are instructive and again something that you study in detail in the class-room ~ or less engagingly online nowadays as ever ~ in preparation for flying airliners.
In fact jetstreams like that in the pic were only discovered circa the 1940s, as either bomber-crews headed for Japan realised they went one way faster than the other or when commercial airliners crashed in the Andes when they figured it must be time to descend when they'd been fighting a headwind all along instead.
Either hemisphere best-viewed as an LP record, you can see that the outside moves faster than the inside and thus a descending column of air incorporates a spin from the surface of the Earth as it does so... clockwise in the northern hemisphere. At the same time descending air produces high pressure, and in doing so it warms and so is less likely to condense to produce either cloud or rain.
Broadly speaking the jets emerge because hot air from the Tropics expands to slide toward the poles, but is transformed into fast-moving rivers of air by a planet that rotates at around 1,000 m.p.h. at the equator. In turn these sinuous rivers produce eddies of rising or descending air, producing the high- and low-pressure systems we enjoy from one week to the next.
Turns out that climate-change, so called because it sounds less like something we caused than global-warming and in the hope it will go away, is affecting the Arctic most of all. Here it is warming at three times the going rate, with Europe at twice the going rate.
This alteration to the status quo at the northern pole apparently allows a jetstream to split as illustrated, which in turn allows for a high-pressure dome to inhabit the continent as shown. Hence temperatures of around 38C in England and 41C in a city once considered delightful to be in during Springtime, or Paris.
I studied (when I could be bothered) what might be called Earth Science nowadays but Geography and Geology back then, and one of the few things that told on me was how the plant loves a positive feedback loop. They often occur over stretches of time, but can be flipped into one or other long-lasting state by, for instance, human interaction or more obvious actors like volcanoes or asteroids.
An easy one to remember for those of us living in urban heat-islands (as the bulk of humanity does), is use of air-conditioning units. These (a) consume fossil fuels at a distance to increase warming on a broader scale and (b) dump hot air externally so as to increase it on a local scale. Which persuades more of us to use them... and so on and so forth until the roundabout spins too fast as it did at Blackpool's Funhouse and we all fall off.
Good pub quiz question though for you:
Q. Which nation has the highest per-capita energy-use?
A. Qatar.
And ladies, gentlemen and the undecided that is because you cannot really function there without moving between air-conditioned homes, shops and workplaces in air-conditioned cars. All of which uses more fossil fuel beside that used to provide water that would otherwise be largely absent.
It's a party, like humanity, that can only go on for so long. Someone I know asked an American ex-pat of the sort who provided the means of extraction from the 1930 on that has allowed for all of this... how it might end?
'Back to the sand from which it came' apparently.
But then we're nothing but dust anyway, are we?
Ed. And you have a good weekend too...
