Jet Stream

Since the progress of an airplane is aided or impeded depending on whether tailwinds or headwinds are encountered. | Jet stream, narrow, swift currents or tubes of air found at heights ranging from 7 to 8 mi (11.3-12.9 km) above the surface of the earth. | They are caused by great temperature differences between adjacent air masses. There are four major jet streams. | In the Northern Hemisphere, the jet stream is sought by eastbound aircraft, in order to gain speed and save fuel, and avoided by westbound aircraft. | Instead of moving along a straight line, the jet stream flows in a wavelike fashion; the waves propagate eastward (in the Northern Hemisphere) at speeds considerably slower than the wind speed itself.