The North Atlantic Jet Stream is born high in the atmosphere, more than 7km from the earth's surface. The temperature difference between the cool Arctic and the warm equator creates a pressure difference, and a narrow band of powerful wind. The turning of the earth makes this strong current, it averages around 170kph, flow from west to east, and helps explain why it is quicker to fly from New York to London than in the opposite direction.
The jet stream was first identified around the turn of the 20th century — early research efforts by scientists even included a few ill-fated voyages in air balloons. Technically there are four jet streams that circle the planet — two in each hemisphere — but the most studied is the northern hemisphere polar jet, due to its central role in European weather patterns. This area of research expanded during the second world war but it was not until the 1980s, and the advent of modern satellites, that really good data on the jet stream and other atmospheric currents became available allowing measurement of its precise speed and direction.
This relatively short time period is part of the reason why it is so hard to tell how the jet stream is being affected by climate change. Unlike temperature records, which stretch back to the pre-industrial era, there is no detailed account of what the jet stream was doing before human-induced global warming kicked in.
"Often in physics you can write down equations and out pops the answer and everyone agrees, but we can't do that with the jet stream," says Paul Williams, professor of atmospheric science at Reading university.
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