Jet Stream

a high-speed westerly wind in the region of the tropopause. The principal jets are the polar front and subtropical jets, which occur at heights between 10 and 15 km. The winter jet stream occurs between 50 and 80 km in the upper STRATOSPHERE. The wind speeds can reach 300 km/h. The air streams move north and south of their general trend, in surges, which are probably the cause of depressions and anticyclones. There are a number of separate jet streams, but the most constant is that of the subtropics. Jet stream speed and location are of importance to high-flying aircraft.

Taken from Dictionary of Science