|jet stream |
A narrow current of strong wind circling the Earth from west to east at altitudes of about 11 to 13 km (7 to 8 mi) above sea level. There are usually four distinct jet streams, two each in the Northern and Southern hemispheres. Jet stream wind speeds average 56 km (34 mi) per hour in the summer and 120 km (74 mi) in the winter. They are caused by significant differences in the temperatures of adjacent air masses. These differences occur where cold, polar air meets warmer, equatorial air, especially in the latitudes of the westerlies.
A narrow band of swiftly moving air found at very high altitudes.
Note: Movements of the jet stream have important (but generally short-lived) effects on weather patterns.
Note: Travel time in an airplane can be lengthened or shortened by the jet stream, depending on the direction of flight and the strength of the stream.