Glossary · Khoa học Trái Đất
Jet stream
A relatively narrow band of strong wind in the upper atmosphere. On Earth, jet streams typically occur around 9,100 m (30,000 ft) up, with winds blowing from west to east.
The winds blow from west to east because Earth rotates: the surface moves east fastest at the equator, slowing to zero at the poles. Air moving from the equator toward the poles keeps its eastward momentum while the surface beneath it slows, so it moves east faster than the ground — the Coriolis effect. Jet streams follow the boundaries between hot and cold air, so the band often shifts north and south; because those boundaries are most pronounced in winter, jet streams are strongest during the winters of both hemispheres. Earth has several different jet streams: the polar jet lies between 50° and 60° latitude in both hemispheres, and the subtropical jet around 30°. They vary in height from about 6 to 13 km (four to eight miles) and can reach speeds of more than 442 km/h (275 mph).
Other planets have jet streams too. Saturn is blanketed with clouds that appear as faint stripes, jet streams and storms; at the north pole a wavy jet stream with winds of about 322 km/h forms a hexagon some 30,000 km across, with a massive rotating storm at its centre.