What is the definition of a jet stream?

A jet stream is defined as a narrow band of strong winds that can exceed speeds of 50 knots. These winds typically occur in the upper levels of the atmosphere, specifically in the tropopause where the temperature gradient is steepest between polar and tropical air masses. The intense winds are a result of the significant temperature differences, which create pressure gradients that drive the fast-moving air.

Jet streams play a critical role in weather patterns by influencing the movement of storm systems and affecting flight routes. They can also impact surface weather, as their position and strength can lead to the formation of high-pressure and low-pressure systems.

The other options describe wind characteristics that do not meet the specific criteria of a jet stream. Weak winds or consistent surface flows do not capture the intensity or the altitude typically associated with jet streams, while slow varying winds imply a lack of the rapid movement that characterizes these high-altitude, powerful winds.