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6.5 Exercise 16: Topographic Steering 131Fig. 6.5 Exercise 16. Scenario 1. Snapshot of fl w f eld (arrows, averaged over 5×5gridcells)andEulerian tracer concentration (crowded lines) after 20 days of simulation. Bathymetric contours areoverlaidξ = f( )ho + Δh− 1h o(6.35)where h o is the initial thickness of the water column, and Δh is the change in thicknessof the water column along the f ow trajectory.In Scenario 1, water-column squeezing over the bottom escarpment leads to afl w whose relative vorticity matches the curvature of bathymetric contours. Thepropagation direction of topographic Rossby waves is the same as that of the ambientfl w, so that these waves propagate rapidly away from their generation zone.Surprisingly, something different happens in Scenario 2 (Fig. 6.6). Here, watercolumnsqueezing over the bottom escarpment creates relative vorticity of oppositesign to that of Scenario 1. In response to this, the f ow crosses bathymetric contoursinto deeper water. This initiates a standing topographic Rossby wave of a wavelengthsuch that its phase speed (given by Eq. 6.28) is compensated by the speedof the ambient fl w. For the configuratio of this exercise, the resultant wave patternattains a horizontal amplitude of 20 km and a wavelength of 50 km. Obviously,situations in which the ambient fl w runs opposite to the propagation direction oftopographic Rossby waves support the creation of such standing waves. Despite theFig. 6.6 Exercise 16. Same as Fig. 6.5, but for Scenario 2