Original: Jet streams , or just jets in context , are fast flowing , narrow air currents found in the atmosphere of planets at the tropopause , the transition between the troposphere ( where temperature decreases with height ) and the stratosphere ( where temperature increases with height ) .
Simplified: Jet streams are fast flowing , relatively narrow air currents found at the tropopause , the transition between the troposphere ( where temperature decreases with height ) and the stratosphere ( where temperature increases with height ) , United States Department of Energy .