Stationary Alternating Quasi-Zonal Jet-Like Structures in the Ocean
Recently, prominent jet-like features of the ocean circulation, with meridional scale of O(300-500 km) and extending for thousands of kilometers in length, have been detected in satellite and in situ observations and in high-resolution numerical models. In this study we focus on quasi-stationary features, called hereafter striations, which are best seen in time-averaged velocity fields. The striations form a near-global system of weak alternating eastward and westward currents embedded into broader and stronger flows, but especially they are distinct in the eastern parts of subtropical gyres. Vorticity budget of the upper ocean layer, evaluated in the subtropical North and South Pacific using 1993-2002 mean dynamic ocean topography, concurrent satellite altimeter observations and output of the Ocean General Circulation Model for the Earth Simulator (OFES), revealed that dynamics of the striations are not consistent with the Rhines mechanism, usually invoked to explain the formation of alternating zonal jets in differentially rotated two-dimensional turbulence. At the same time, transient eddies interact with the time-mean striations. The latter, therefore, cannot be reduced to a kinematical artifact of time-averaging of westward propagating eddies. We discuss an alternative hypothesis that striations result from non-linear beta-plumes generated by compact in extent PV anomalies at the eastern ocean boundary.