Jet Streams are air currents found in the stratosphere and tropopause being is located about 6 to 15 miles above the Earth surface. They are fast flowing bodies of air moving in the same direction and consist of relatively the same temperature. Jet streams form near boundaries of air masses adjacent to themselves, which consist of a signifigently different temperature. An example of where a jet stream would form would be the warmer air to the south of the polar region. A typical jet stream will be 1000s of miles long usually spanning over continents and oceans and about a 100 miles wide. Unlike its huge size in width and length, a jet stream can be a small a 100 feet thick usually ranging from 500ft to 1000ft.
The most major jet streams are found in the Northern Hemisphere partly due to the presence of Rossby waves. These are waves that move westward relative to the direction of flow in which they are contained. This along with other factors causes jet streams to have a meandering shape as well as the tendency to flow from west to east with respect to the Earth. Polar jet streams tend to be more near the 60-degree latitude area of the Earth and are closer to the ground, typically 6 to 10 miles above the earth surface. Tropical jet streams are located more toward the 30-degree latitude line.
In the subtropical latitudes there are two main jet streams and the weaker one is located closer to the equator. The subtropical jet stream is an upper level jet stream and is located anywhere from 8 to 15 miles above the Earths surface. The upper level jet stream is said to follow the sun. This is because during the summer month the jet stream moves more north in the summer and more south in the winter. The further you get from the equator the closer the jet stream becomes to the surface. Low-level jet streams are also found in the tropical regions but are more prominent during the summer months and tend to be more easterly. These can evolve into oncoming fronts and high-pressure cells.
In the aviation world meteorologists use the location of the jet stream as an aid in weather forecasting. Flight time can be affected by either flying with or against the stream. Airliners also have certain hazards that can in some situations be fatal to the flight. One type of hazard is clear-air turbulence. Typically found in a jet stream's vicinity, clear-air turbulence forms around the boarders of jet streams or in the areas at or between the convergence of two jet streams. Since jet streams are directly affected by temperature difference when two jet streams meet with a significant temperature difference then the potential for clear-air turbulence because great. Though turbulence is not one of the most understood weather phenomena, it can in some cases be predicted though the use of jet stream charts and this allows awareness of potential danger.