The M2 internal tide evolution in the Bay of Biscay is shown here by several movies.
The animations are displayed on the zoom area in white, plotted on the following figure.
The view point is from the North-West direction.

In the movies, - the French continental slope is on the left,
                         - the Spanish continental slope is on the right.
To go on the movie click on the picture.
To go out close the  movie window.
More informations on the model.
 
 

MICOM model calculates the evolution of the baroclinic variables (current and thickness of the different layers) from  initial conditions corresponding to null baroclinic currents and  flat thickness on the horizontal plane (see 3D Micom results). These two  movies present the transient state when the internal tidal wave and associated baroclinic currents are generated. These one  show the different generation areas and the different direction of propagation of the wave.
Two main sections are shown :
- Movie 1, the evolution of the North-South baroclinic current  on the horizontal plane, in the first layer.
- Movie 2, the evolution of the North-South baroclinic current on a vertical section defined  by a dotted line on the movie 1.
The different views correspond to the spatial evolution at the following lunar days: 1-2-4-6-8-10-12-14-16-18-20, the transient state being defined by the five first steps.
 
 

- Step 1 Day 1: One can see the generation area over the French continental slope with two maxima of current on each side of the shelf break , i.e over the continental shelf and over the continental slope.

- Step 2 Day 2: On each side of the French shelf break,  it appears the internal tide wavelength defined by the seasonal thermocline (the third mode named the "interfacial mode"). At the same time, on can see a maximum in the current amplitude in the middle of the Bay of Biscay : it is the fact of the first baroclinic mode defined by the deep ocean stratification and which propagates more quickly than the third one.
At this time step, the internal tide energy mainly comes from the French continental slope.

-  Step 3 Day 3: Most of the first "deep ocean" baroclinic mode appears in the whole domain. One observe a maxima area of surface current close to the Iberic slope which corresponds to an internal tide coming from the Iberic slope along the second upward energetic ray.

- Step 5 Day 8: The internal tide energy of the first modes is propagated on the whole domain.  After this time step there are only spatial adjustments in the current repartition due to the propagation of the high baroclinic modes which have a weaker celerity than the first ones.
 
 

On the vertical plane, we find again the well known repartition of the internal tide energy along characteristic rays (defined by the stratification and by the M2 tide frequency). The first mode (characterized by maxima of currents near the bottom and near the sea surface)  appears very quickly (step 2, day 2), whereas the other one are all propagated only after time step 5 (day 8). These vertical modes are charaterized by cores of maximum of current along the rays.
 
 

The same two main sections as hereabove are now displayed over one tidal cycle: each view corresponds to one "lunar" hour of the tidal cycle (12 steps).

- Movie 3, the evolution of the North-South baroclinic current on the horizontal plane, in the first layer.
- Movie 4, the evolution of the North-South baroclinic current on a vertical section defined  by a dotted line on the movie 1.
 
 

The spatial evolution of the internal tide (North- south baroclinic current) is now presented by successive vertical sections perpendicular to the French continental slope, with the same orientation as hereabove. The purpose is to explain the origin of the areas of maxima of surface current one can see on the horizontal plane.
 
 

- Just in front of the view, there is a variation of the bottom topography, which corresponds to a flat zone by about 2000m of water depth and named the "plateau de Meriadzeck". For vertical sections coming from this area, the bottom slope is lower than the characateristics slope, and the first internal tide ray is an upward ray : it induces a maximum of surface current (by 47.5N, 9W (see 3D Micom results, section 4)) closer to the French continental slope than for the other sections, where the first ray is a downward ray.
- Then, there are two other energetic sections, with maxima of surface current by  46.10N , 7.5W  and 44.50N,  5.30 W  (see 3D Micom results): for these sections the bottom slope is upper than the one of the characteristic rays, and therefore these maxima correpond to the resurgence of the second ray.
 
 

The horizontal baroclinic vector is plotted here along the most energetic vertical section, to show its evolution on a tidal cycle.

- The baroclinic current turns clockwise as the barotropic tidal current over the French continental shelf.
- There are strong vertical shears of current which are not at the same depth for the different points of this vertical section. It is due to the particular propagation of the energy along the rays. Over the plain, there are about two or three vertical shears on a vertical profile, which show that the three first modes are preponderant.
- Above the French continental slope, on the third vertical profile, there is an opposition in phase between the bottom and surface currents. This shear has already been observed on data collected in this area by doppler current meters (see data collected in the Bay of Biscay, point PF06).