Jetstrøm

Jetstrøm, also referred to as jet stream, is a narrow, fast-flowing ribbon of air in the upper levels of the atmosphere, typically found near the altitude of the tropopause. The primary jet streams are the polar front jet streams, located around 30–45° latitude in both hemispheres, and the subtropical jet streams in the mid-latitudes. These currents are driven by large-scale temperature gradients between the equator and the poles; the greater the gradient, the stronger the resulting wind shear that creates the jet.

The polar jet streams are strongest in winter when polar temperatures drop significantly, producing a steep temperature gradient. This results in winds with surface affective wind speeds of up to 200 km/h in the troposphere, and even faster in the jet level. The southern hemisphere polar jet reaches its maximum prevalence and speed during the southern winter, showing a notable seasonal lag relative to the northern hemisphere because of the uneven distribution of landmass.

Jet streams influence weather patterns by steering large-scale weather systems over continents. They serve as guides for storm tracks, affecting the trajectory, speed, and intensity of cyclones. By modulating the passage of warm and cold air masses, jet streams play a crucial role in determining temperature, precipitation, and the development of severe weather events.

In climate science, monitoring the position, strength, and meandering (atmospheric Rossby waves) of jet streams provides insights into changes in atmospheric circulation associated with global warming. Since the mid-twentieth century, several studies have documented northward shifts and increased variability in jet stream patterns, correlating with regional climate change impacts such as altered storm tracks and increased frequency of extreme weather events. The study of jet streams thus remains central to meteorology, atmospheric physics, and climate research.