Jet stream consists of ribbons of very strong winds which move weather systems around the globe. These streams are found 9-16 km above the surface of the Earth, below the tropopause.

How Are They formed?

Jet streams are formed by a combination of a planet’s rotation on its axis and atmospheric heating (by solar radiation and, on some planets other than Earth, internal heat). Jet streams form near boundaries of adjacent air masses with significant differences in temperature, such as the polar region and the warmer air towards the equator.

How They Work?

Here is a you tube video showing how jet streams are formed and how they work.

How does the jet stream affect the weather?

The position of a jet stream varies within the natural fluctuations of the environment. What happens in one part of the world depends on what is happening elsewhere – the atmosphere is a complete environment with numerous connections.

Waves or ripples along the jet stream can cause Atlantic depressions to deepen explosively as they are steered towards the UK, so they are very important to meteorologists.

The major jet streams on Earth are westerly winds (flowing west to east). Their paths typically have a meandering shape; jet streams may start, stop, split into two or more parts, combine into one stream, or flow in various directions including the opposite direction of most of the jet. The strongest jet streams are the polar jets, at around 7–12 km (23,000–39,000 ft) above sea level, and the higher and somewhat weaker subtropical jets at around 10–16 km (33,000–52,000 ft). The Northern Hemisphere and the Southern Hemisphere each have both a polar jet and a subtropical jet. The northern hemisphere polar jet flows over the middle to northern latitudes of North America, Europe, and Asia and their intervening oceans, while the southern hemisphere polar jet mostly circles Antarctica all year round.

Jet streams are caused by a combination of a planet’s rotation on its axis and atmospheric heating (by solar radiation and, on some planets other than Earth, internal heat). Jet streams form near boundaries of adjacent air masses with significant differences in temperature, such as the polar region and the warmer air towards the equator.

Other jet streams also exist.

During the Northern Hemisphere summer, easterly jets can form in tropical regions, typically in a region where dry air encounters more humid air at high altitudes. Low-level jets also are typical of various regions such as the central United States.

How does the jet stream affect flights?

Meteorologists use the location of some of the jet streams as an aid in weather forecasting and many other things. The main commercial relevance of the jet streams is in air travel, as flight time can be dramatically affected by either flying with the flow or against the flow of a jet stream. Clear-air turbulence, a potential hazard to aircraft passenger safety, is often found in a jet stream’s vicinity, but it does not create a substantial alteration on flight times.

Source(s):

http://www.metoffice.gov.uk/learning/wind/what-is-the-jet-stream

http://en.wikipedia.org/wiki/Jet_stream