Fig. 2. Summary schematic showing the changes in ellipse format at surface and bottom due to the onset of stratification in the Rhine ROFI and the resulting semi-diurnal oscillations in stability driven by tidal straining.
(a) Stirring by windstress tw and bottom stresses in the tidal flow. Tidal ellipses are close to degenerate.
(b) After a reduction in stirring, the horizontal density gradients relax under gravity with the constraint of rotation. The cross-shore displacements induce stratification which modifies the tidal dynamics so that the ellipses become anticyclonic at the surface and cyclonic near the seabed.
(c) The cross-shore shear produced by the modified tidal ellipses acts on the horizontal density gradient to generate semi-diurnal oscillations in the stratification.
(d) A subsequent increase in stirring re-imposes vertical uniformity, the ellipses revert to near degenerate form so that the cross-shore shear and the associated oscillations are suppressed.
