Illustration showing the paths of the jet streams around the globe. Jet streams are fast flowing high-altitude narrow air currents that circle the Earth. The major ones on Earth are the polar jet stream (7-12 km altitude, blue) and the subtropical jet stream (10-16 km altitude, red), which occur in both hemispheres. Also shown are Hadley cells in the tropics, where the winds flow from east to west, and mid-latitude Ferrel cells, where the winds flow from west to east. For an unlabelled version of this image see C057/9080.