DAUNTLESS Dotty has an important place in the history of meteorology; it was she, allegedly, who discovered the existence of the jet stream in November 1944. Dotty, apparently, was the lead aeroplane of a group of B29 bombers which took off westwards from the US on the first high level bombing mission to Japan in the closing months of the second World War. The flight encountered unexpected head winds of unprecedented strength, which proved to be a more formidable adversary than the enemy's anti aircraft guns and fight planes: Dotty was the first to experience the previously unsuspected jet stream on the nose.
The jet stream is a narrow ribbon of very strong winds in the middle latitudes, which may lie anywhere between 25,000 and 40,000 feet above sea level. It varies in width from 60 to 300 miles and the wind at its core typically blows at speeds of 100 to 150 m.p.h. winds as strong as 300 m.p.h. have been experienced on a number of occasions.
This slender tube of high speed wind is in sharp contrast to the much quieter atmosphere surrounding it, with the wind speed dropping off very sharply at its edge, and also above it and below. It is orientated in a roughly west to east direction, sometimes relatively straight but often meandering in a wavy U shaped pattern. It is caused by a very sharp contrast of temperature in the horizontal, a local exacerbation of the otherwise gradual increase in temperature from the pole to the equator and its position usually roughly coincides with that of the polar front at lower levels of the atmosphere.
American meteorologists, unlike their European counterparts, like to make a feature of the jet stream in the forecasts. No television presentation is complete without a shot of broad red wavy line.
Meandering across the Great Plains or further north or south, to convey a pictorial impression of the general character of the weather over a large sub continent like the US.
Its usefulness is twofold. Firstly, since it indicates the approximate position of the polar front, it also delineates the average track of the most vigorous depressions on the weather map, and therefore the zone which the most active weather is likely to be concentrated. Secondly, and for the same reason, its meandering path provides a convenient dividing line between the cold polar air to the north, in which harsh wintry conditions are likely to be prevalent and the much milder air of semi tropical origin further south.