Jetstream

noun (countable)

/ˈdʒɛtstriːm/

A narrow band of fast-moving upper-tropospheric wind, typically at 9–16 km altitude, with core speeds commonly 150–300 km/h, driven by strong horizontal temperature gradients (baroclinicity) between adjacent air masses. The two primary jet streams — the polar jet and the subtropical jet — meander latitudinally through Rossby waves, steering mid-latitude weather systems. For UPSC, the Western Disturbances that bring winter rain to northwest India travel along the subtropical jet stream at about 25–30°N, while the shift of the jet stream in June triggers the onset of the southwest monsoon over Kerala.

✍️ Usage in a UPSC answer

The abrupt northward shift of the subtropical jet stream from approximately 28°N to beyond 30°N in late May or early June is now operationally recognised by the India Meteorological Department as one of the primary large-scale triggers for the onset of the southwest monsoon.

Synonyms

upper-level jettropospheric jetwind maximumaerial river (informal)polar front jet

Antonyms

surface windland breezesea breezedoldrumsequatorial calm

🌱 Word Family

jet stream (noun), jetstream (noun, variant), jet-stream axis (compound noun), polar jet (compound noun), subtropical jet (compound noun)

🔡 Root

German Strahlstrom = jet stream (literally 'beam current'); English term from jet (a fast stream) + stream

📜 Etymology

The phenomenon was discovered by Japanese meteorologist Wasaburo Ooishi in the 1920s through balloon observations, but the English term 'jet stream' was coined by German-American meteorologist H.C. Seilkopf in 1939 and popularised during World War II when high-altitude bombers encountered these winds over Japan. The word derives from jet (a forceful stream, from French jeter = to throw) combined with stream.

🧠 Memory Hook

JET stream = a JET PLANE's highway in the sky. UPSC tip: the jet stream's seasonal migration is the 'on/off switch' for India's monsoon — when it jumps north over the Himalayas, the monsoon floods in from the south.

🌍 Geography 📖 Seen in: Plate Tectonics & Volcanism — Continen...

Tip: press Alt+S to hear pronunciation