The Jet Stream flows in a more or less continuous band around the globe
from west to east. It is caused by the changes in air temperature where
the cold polar air moving towards the equator meets the warmer equatorial
air moving north. It is an area of strong winds that are concentrated in
a relatively narrow band in the upper troposphere of the middle latitudes
and subtropical regions of the Northern and Southern Hemispheres. It is
marked by a concentration of isotherms and strong vertical shear.