What jet streams?

The lowest layer of the atmosphere is called the troposphere. Above it is the second layer, the stratosphere. Around the border between the two layers are strong winds, called jet streams, which blow mostly from west to east at over 160 km/h (100mph). Pilots avoid flying into them, but they often use them as tail winds, so as to increase their speed and save fuel. Jet streams also influence the movements of weather systems in the troposphere.