A Prograde Jet Driven by Rossby Waves

Abstract

Waves are forced by moving sources and sinks of mass on a beta-plane with Ekman friction. If the motion is retrograde and not too fast, these are Rossby waves with a nonzero Reynolds stress u?v??. This stress forces a meridional mass flux which builds up a pressure gradient to allow a compensating mass flux in the Ekman layer. In a rotating system, this meridional pressure gradient requires a zonal flow u?(y)=??/?y(u?v??)/E½Ω,which is also the momentum accumulated by the Reynolds stress in one spindown time. An example shows how excitation of Rossby waves brings momentum into the source of energy, causing a prograde jet there, with retrograde currents on each side. A laboratory experiment confirms the theory, which is proposed as an explanation of the observed ?negative viscosity? of the jet stream in the atmosphere and the Gulf Stream in the ocean.