Jet Stream

A narrow band of very fast, high-altitude westerly wind, typically found near the tropopause where cold polar air meets warmer air to the south, strong enough to cut hours off an eastbound flight and add them to a westbound one. Pilots crossing the Pacific during the Second World War were among the first to report winds of the strength now known, though the Japanese meteorologist Wasaburo Oishi had tracked similar high-altitude currents by pilot balloon in the 1920s, publishing in Esperanto to a readership that mostly missed it. The theoretical account of how such jets form, tied to the same air-mass boundaries the Bergen School mapped at the surface, came together over the following decades.