Jet stream

Jet streams are fast flowing, narrow air currents in the atmosphere. It is the physical mechanism of a teleconnection. The main terrestrial jet streams are located near the altitude of the tropopause and are westerly winds, flowing west to east around the globe. The Northern Hemisphere and the Southern Hemisphere each have a polar jet around their respective polar vortex at around 30,000 ft (5 mi; 9 km) above sea level and typically travelling at around 110 mph (180 km/h) although often considerably faster. Closer to the equator, somewhat higher and somewhat weaker, is a subtropical jet. The northern polar jet flows over the middle to northern latitudes of North America, Europe, and Asia and their intervening oceans, while the southern hemisphere polar jet mostly circles Antarctica. Jet streams may start, stop, split into two or more parts, combine into one stream, or flow in various directions including opposite to the direction of the remainder of the jet. The El Niño–Southern Oscillation affects the location of the jet streams, which in turn affects the weather over the tropical Pacific Ocean and affects the climate of much of the tropics and subtropics, and can affect weather in higher-latitude regions. The term "jet stream" is also applied to some other winds at varying levels in the atmosphere, some global (such as the higher-level polar-night jet), some local (such as the African easterly jet). Meteorologists use the location of some of the jet streams as an aid in weather forecasting. Airlines use them to reduce some flight times and fuel consumption. Scientists have considered whether the jet streams might be harnessed for power generation. In World War II, the Japanese used the jet stream to carry Fu-Go balloon bombs across the Pacific Ocean to launch small attacks on North America. Jet streams have been detected in the atmospheres of Venus, Jupiter, Saturn, Uranus, and Neptune.