A Prograde Jet Driven by Rossby Waves

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  • 1 Oceanography Department, Florida State University, Tallahassee, FL 32306
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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 uv′¯. 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
uyuvE½
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.

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 uv′¯. 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
uyuvE½
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.
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