Jet Stream

A jet stream is a narrow band of strong winds in the upper troposphere near the tropopause, typically 9 to 12 km high, with core speeds of 50 to over 100 knots and peaks above 200 knots in winter. It forms where horizontal temperature gradients are sharp, by the thermal-wind relation, so the polar-front jet lies over the polar front near 50 to 60 degrees latitude and the subtropical jet near 30 degrees marks the poleward edge of the Hadley cell. Jet streaks and the troughs and ridges of the meandering Rossby-wave pattern steer surface cyclones and concentrate baroclinic development. Following the jet shortens eastbound flights.