Final answer:
The jet stream is a fast-flowing, narrow air current that can significantly influence weather patterns and is utilized by aircraft to improve efficiency during flights.
Step-by-step explanation:
The jet stream is a fast-flowing, narrow air current found in the atmospheres of the Earth and other planets. On Earth, jet streams are located near the altitude of the tropopause and are westerly winds (flowing west to east). Their paths typically have a meandering shape, and they can have profound effects on the weather, including severe weather patterns such as storms.
Jet streams are caused by a combination of planetary rotation and atmospheric heating (via solar radiation and other means). Atmospheric heating causes air masses of different temperatures to interact, resulting in high-altitude winds with considerable velocity. Jet aircrafts often use these streams to save fuel and time during flight, by either riding with the flow or avoiding it when it's a headwind.
Given an example of a jet airplane flying from Darwin, Australia, with an airspeed of 260 m/s south of west and the jet stream's wind at 35 m/s south of east, we would calculate the airplane's velocity relative to the Earth by accounting for both the plane's air speed and the direction and speed of the jet stream.