June 3 Andrew Thompson DAMTP - University of Cambridge Vacillating jets:  baroclinic turbulence and topography
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Observations from satellite altimetry and output from high-resolution ocean models indicate that the Southern Ocean is characterized by an intricate web of narrow, meandering, filamentary jets.  These jets undergo spontaneous formation, merger and splitting events, and rapid latitude shifts over periods of weeks to months.  The role of topography in controlling jet variability is explored using a doubly-periodic, forced-dissipative, two-layer quasi-geostrophic model.  The system is forced by a baroclinically-unstable, vertically-sheared mean flow in a domain that is large enough to accommodate multiple jets.  The dependence of (i) meridional jet spacing, (ii) time scales of jet variability and (iii) large-scale, domain-averaged transport properties on changes in the length scale and steepness of simple sinusoidal topographical features is analyzed.  Unsteady jet behavior is found to occur when the characteristic length scale of the eddies is comparable to or smaller than the scale of the topography.  In particular, specific cases are considered where jets may drift across mean potential vorticity gradients or undergo periodic transitions between topographically-steered and zonal structures.  The potential for these processes to play a role in the dynamic nature of Southern Ocean jets is discussed.