Jet streams

You may have noticed that when you look into the sky, clouds at different levels move in different directions.

Within the troposphere, there are two zones of high winds. These are called the "Jet Streams" and they move perpendicularly to the vertical wind cells previously discussed. These winds move from east to west rather than from the north to south or vice versa. At the Polar Front, the region along where the cold and dense polar air mass meets the warmer and less dense tropical air, there is a large temperature difference. Due to this large temperature difference there is a correspondingly large pressure difference which causes significant high level winds perpendicular to the front. These winds are known as the Polar Front Jet Stream. There is a similar temperature and pressure difference that occur at high levels between the Ferrel and Hadley Cells that create winds known as the Sub-tropical Jet Streams. Jet streams are defined as being those winds that exceed velocities of 30 m/s.