A torrent.

A strong and narrow airflow in the upper troposphere or stratosphere. It is generally thousands of kilometers long, hundreds of kilometers wide and several kilometers thick. The long axis of the jet center is called the jet axis, which is almost horizontal. Near the axis of the jet, the shear of wind speed is very strong, the vertical shear is about 5 ~ 10 m/s per kilometer, and the horizontal shear is about 5 m/s per hundred kilometers. According to the regulations of the World Meteorological Organization, the lower limit of the wind speed on the jet axis is 30m/s. The jet winds around the whole hemisphere, and the wind speed on the jet axis is uneven, with one or more maximum wind speed centers. Interrupt when the wind speed is less than 30m/s ... Generally, the wind speed at the center of the jet is 50 ~ 80m/s, sometimes it can reach 100 ~ 150m/s in winter, and occasionally it can reach150 ~180m/s. In some areas, the axis of the rapids branches, and in some areas, two rapids meet. The distribution and structure of the jet can be seen from the isobaric surface near the tropopause (such as 200 hectopascals) and the average zonal wind speed distribution map (see atmospheric circulation). Because jet is related to the transport of atmospheric heat and angular momentum, it is an important link in global atmospheric circulation. Jet stream is often associated with front area, so it is closely related to the occurrence and development of weather system. Jet stream is one of the important research topics in meteorology.

At the end of World War II, American pilots encountered high-speed airflow when flying westward near the tropopause over Japan, which made navigation difficult. After meteorologists' research, they found that this is the westerly jet at high altitude. With the establishment of high-altitude detection network, the existence of high-altitude jet was found over other areas. However, westerly jet, which is located on the coast of East Asia and over Japan, is the most powerful. Because the wind speed of the jet stream is sometimes very high and its vertical and horizontal shear is very strong, it is easy to cause flight accidents when the aircraft flies along the jet stream near the jet stream area or in the shear zone with strong wind speed (see aviation meteorology). Therefore, it is often required to provide accurate information and forecast of jet position and intensity in time. According to the formation area and structure of jet stream, it can be divided into polar front jet stream, subtropical jet stream, tropical easterly jet stream and extreme night jet stream. The low-level jet in the lower troposphere is another kind of jet.