Final answer:
The polar jet stream is a fast-flowing air current found at the boundary of the Earth's troposphere and stratosphere, primarily at the 250 to 300 millibar level. It shapes our weather patterns by redistributing temperatures and is similar to jet streams found in the atmospheres of Jupiter and Saturn.
Step-by-step explanation:
The polar jet stream is a fast-flowing river of air at the boundary between the Earth's troposphere and the stratosphere, typically found between 6 and 14 miles (10 to 22 kilometers) above the surface at the level of the tropopause. Its role is to influence weather patterns and the movement of storm systems by reshaping the temperature distribution across regions. On upper air charts, the polar jet stream is best observed at the 250 to 300 millibar level. These powerful east-west wind patterns do not significantly change over many decades and are similar to the jet streams observed in the upper atmospheres of the giant planets like Jupiter and Saturn.
Even in Jupiter's upper atmosphere, jet streams are apparent, flowing eastward at the equator with speeds of about 90 meters per second (300 km/h), like those on Earth. Besides influencing weather, jet streams have an effect on the thermal structure of the atmosphere and are related to various atmospheric phenomena including the formation of polar stratospheric clouds and the depletion of the ozone layer.