Why do jet streams form

The result is the wind moves faster than the earth rotates so it moves from west to east relative to us at the surface. The Coriolis effect. Please Contact Us. Toggle navigation JetStream. The Jet Stream How the earth's rotation effects the west to east direction of the jet stream. North hemisphere cross section showing jet streams and tropopause elevations.

The strength of the wind increases toward the core of the jet stream. It also does not reside at any one particular height but can extend across hundreds of mile wide and 1,s of feet in height. Cross section of the jet stream. Disclaimer Information Quality Help Glossary. Jet streams exist because of a difference in temperature between two air masses. As the warm air expands, it becomes lighter and creates a warm air current. The denser cold air then sinks to replace the warm air and creates a cool air current.

When these air currents are formed high in the atmosphere, they are known as jet streams. The greater the difference in temperature, the stronger the winds within the jet stream.

Winds within a jet stream are normally between 80 to miles per hour , but they can reach more than miles per hour. While jet streams are situated high above the earth, they also shape weather patterns on the ground far beneath them. Jet streams are always in motion, changing speed, moving up and down, looping around, buckling, shifting their flow, or breaking up.

However, jet streams can move in different ways, creating bulges of winds to the north and south. With this technology, meteorologists can detect the location of the jet streams. The moving band of air between the two is the polar jet stream. Monitoring jet streams can help meteorologists determine where weather systems will move next. But jet streams are also a bit unpredictable. Their paths can change, taking storms in unexpected directions. A jet stream forms high in the upper troposphere between two air masses of very different temperature.

The greater the temperature difference between the air masses, the faster the wind blows in the jet stream. This river of air has wind speeds which often exceed mph, and sometimes peak over mph. Jet streams usually form in the winter, when there is a greater contrast in temperature between cold continental air masses and warm oceanic air masses. The following image shows an example of this from the National Weather Service's Aviation computer forecast model:.

But how does the temperature difference between two air masses cause the jet stream? Since colder air is more dense than warmer air, there is an air pressure difference between them at any altitude.