have little observational support, the Gibraltar Experiment dataset showing some
hints of them [11].
The great asymmetry of the occurrence of eastwards versus westwards progressing wave trains lies in the background flow mean state. Figure 3 sketches two
possible states, the first one (left panels) with a motionless stratified water column
over a rough topography (sill), the second one (right panels) with a steady baroclinic exchange. When strong enough oscillating tidal currents are superimposed to
the background state, the flow-topography interaction gives rise to the formation of
symmetric hydraulic jumps in the first case, but not in the second one. When the
jumps decay, they in turn originate wave trains progressing away from the sill in
Fig. 3 Simplified sketch of the formation of hydraulic jumps and internal waves in a stratified
(two-layer) flow over marked bathymetry (sill, deep grey shade). Panels a and b show the
background situation in cases of no flow and steady baroclinic exchange, respectively. Panels
c and d illustrate the result of (the same) barotropic tidal forcing on both background states when
tidal currents point to the left. They lead to the eventual formation of hydraulic jumps (HJ)
downstream of the sill, with the jump corresponding to the baroclinic mean exchange (panel d)
showing greater amplitude. Panels e and f do the same for tidal currents pointing to the right.
Again, an asymmetry appears with the jump formed in the no-flow background state (panel
e) being larger than the counterpart of the mean baroclinic exchange (panel f). In both cases, the
asymmetry arises from the different background states, which enhances (reduces) the total deep
current when tidal currents point to the left (right) under steady baroclinic exchange. The
short-wave packets propagating on the interface would represent the internal waves generated
during the previous tidal cycle. These wave packets have similar probability of occurrence in either
direction in the no-flow background state (panels c and e) but not in the baroclinic mean exchange
(panels d and f) where the right-going waves are formed much more frequently
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J. García-Lafuente et al.
hints of them [11].
The great asymmetry of the occurrence of eastwards versus westwards progressing wave trains lies in the background flow mean state. Figure 3 sketches two
possible states, the first one (left panels) with a motionless stratified water column
over a rough topography (sill), the second one (right panels) with a steady baroclinic exchange. When strong enough oscillating tidal currents are superimposed to
the background state, the flow-topography interaction gives rise to the formation of
symmetric hydraulic jumps in the first case, but not in the second one. When the
jumps decay, they in turn originate wave trains progressing away from the sill in
Fig. 3 Simplified sketch of the formation of hydraulic jumps and internal waves in a stratified
(two-layer) flow over marked bathymetry (sill, deep grey shade). Panels a and b show the
background situation in cases of no flow and steady baroclinic exchange, respectively. Panels
c and d illustrate the result of (the same) barotropic tidal forcing on both background states when
tidal currents point to the left. They lead to the eventual formation of hydraulic jumps (HJ)
downstream of the sill, with the jump corresponding to the baroclinic mean exchange (panel d)
showing greater amplitude. Panels e and f do the same for tidal currents pointing to the right.
Again, an asymmetry appears with the jump formed in the no-flow background state (panel
e) being larger than the counterpart of the mean baroclinic exchange (panel f). In both cases, the
asymmetry arises from the different background states, which enhances (reduces) the total deep
current when tidal currents point to the left (right) under steady baroclinic exchange. The
short-wave packets propagating on the interface would represent the internal waves generated
during the previous tidal cycle. These wave packets have similar probability of occurrence in either
direction in the no-flow background state (panels c and e) but not in the baroclinic mean exchange
(panels d and f) where the right-going waves are formed much more frequently
196
J. García-Lafuente et al.