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Jet Stream

August 23, 2007

A listener asks: What causes the jet streams?


What drives the jet streams? I’m Bob Hirshon and this is Science Update.

Justin Huebner from Oklahoma City emailed us to ask what causes the jet streams, and why they’re so narrow. We asked University of Utah meteorologist Thomas Reichler. He explains that in both the Northern and Southern hemispheres, warm air from the tropics rises until it can’t get any higher, then diverges toward the poles. There, the surface of the earth spins more slowly.

THOMAS REICHLER (University of Utah):
So as the air moves towards the poles, it tries to retain its angular momentum and therefore speeds up.

As for why they’re narrow, Reichler says that’s sort of a misconception. He says the jet streams depicted on most diagrams and satellite maps are oversimplified, and that the wind speeds actually peter out very gradually as you move away from the stream’s center. I’m Bob Hirshon, for AAAS, the science society.