18.10.2012: FB1-Seminar

11.00-12.00 Hörsaal West:, Düsternbrooker Weg 20

Abstract:

Energy diagnoses are useful for illustrating (i) the effect of bottom topography on currents and waves, and (ii) the interaction between currents and waves.  Concerning (i) the topographic effect, kinetic energy can be decomposed into that associated with the barotropic (depth-averaged) and baroclinic (residual) component of velocity. In the classical studies of the Antarctic Circumpolar Current (ACC), the depth-integrated balance of momentum has been explained by the cancellation of wind stress and the difference of pressure upstream and downstream of a bottom ridge, which can be interpreted as the case of barotropic kinetic energy being converted to potential energy. In the studies of tidal internal waves, bottom topography allows barotropic kinetic energy to be converted to potential energy and then to internal wave energy. Concerning (ii) the current-wave interaction, thickness-weighted-mean momentum equations in a vertically Lagrangian (VL) and horizontally Eulerian coordinate system have been sometimes used to explain the vertical redistribution of momentum of basic currents by the residual effect of pressure perturbations associated with baroclinic instability or wind-induced wave generation. An energy diagram associated with the VL framework can be obtained if the definition of the mean and wave kinetic energies is modified. Regardless of mesoscale eddies or surface waves, the VL framework allows an exact and concise treatment of the top and bottom boundary conditions of the ocean.