concept

Jet stream

A narrow, fast ribbon of wind near the tropopause. On Earth its cores sit around 7–12 km up, typically running 30–60 m/s and topping 100 m/s in winter, while the ribbon itself is only 300–600 km wide — a thread compared with the circumference it wraps. The common misconception is that it is a fixed band pinned to the map: it is not. It meanders, migrates in latitude with the seasons, splits and rejoins, and it is those wanderings rather than the average position that set the weather underneath.