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Ooops, got it back to front.
Interesting thing, the Jet Stream.
The Jet stream.
Huge volumes of air of different temperatures are rising and falling at the point where the two cells meet and the boundary shifts constantly, waving snake-like, north and south, as one cell expands against the other, only to contract as pressure builds on the other side. This is not a fixed line around the world but, if it could be made visible, would be more akin to an ever-changing battleground where one army pushes polewards with reinforcements of warm air, only to be repulsed by greater quantities of cold pressing the other way. The result is to create huge differences in pressures in the air aloft, and just as any wind on the ground is created by differences in pressure between blocks of air, so very strong winds build up at the top of the boundary, creating fast-moving rivers of air that encircle the planet. These are the Jet Streams, current of air typically hundreds of kilometers long, 100 kilometers wide and a kilometer or more deep, which can reach speeds of 300-500 kilometers per hour.
Taken from the book 'Wild Weather'. BBC TV series
Ken
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