Laboratory model of a planetary eastward jet

The concentration of eastward planetary currents into strong wavy jets is a major feature of the atmospheric general circulation (for example, the jet stream) and of oceanic currents (for example, the Gulf Stream east of Cape Hatteras). These strongly nonlinear jets are, however, not well understood. Here we describe experiments in which we have produced similar jets in a rotating annulus with mechanical forcing: the Coriolis force acting on fluid pumped radially inward from a ring of sources to a ring of sinks results in a strong eastward jet. For a wide range of parameters the jet has a robust wavy shape, as shown in Fig. 1. The wave velocity and wavelength of these Rossby waves are accounted for by simple scaling arguments. Experiments with dye injected into the fluid show that the jet acts as a barrier to tracer transport (see Fig. 1e), much as the southern polar night jet may act as a barrier to the transport of ozone from lower latitudes into the polar region1. Our observations are insensitive to the details of the arrangement of the sinks and sources.