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Unexpected result with 3 layers: Run exp2_g

Summary

A new experiment has been performed. It is similar to exp2_e except it has now 3 layers. The layers have the same thickness than in previous simulations, 500 m each.

Basically, the Eulerian mean flow has the same structure in the 3 layers but is weaker downward.

Based on estimate from the zonal displacement of salinity anomaly, the Lagrangian mean flow seems to follow the same rule: it has the nearly same structure in layer 3 than in the two other layers but it is weaker.

Causes of these unexpected results are discussed.

Results

The zonal Eulerian mean flow from day 400 to 500 is shown in Fig. 1. The mean flow has the same structure in the 3 layers but is weaker downward. The same is true of the Lagrangian mean flow estimated from the displacement of salinity anomaly initialized at day 500. Fig. 2 shows the salinity anomaly after one cycle, at day 600.Again, the Lagrangian mean flow is the same in all three layers except that it weakens downward. Notice, however, that the eastward displacement near y=1110 km is weaker than the westward displacements, unlike in the upper two layers.

../../../../../_images/mu_d400_500_exp2_g.png

Figure 1: 400-500-day mean U in exp2_g.

../../../../../_images/Salt_disp_d600_exp2_g.png

Figure 2: Salt anomaly at day 600. The anomaly has been initialized at day 500.

The wave flow, on the other hand, appears to be barotropic as shown by a snapshot of the zonal velocity at day 400 (Fig. 3). Thus, we expect the Stokes drift part of the flow to be barotropic and the cause of the decay of the Eulerian mean flow with depth should be due to the Lagrangian mean flow alone. However, if there was really no friction but the surface and bottom ones, we would have expected no Lagrangian displacement in the middle layer. There is thus something wrong. Maybe, there is a vertical stress that I have not been disregarded.

../../../../../_images/u_d400_exp2_g.png

Figure 3: Snapshot of the zonal velocity on day 400.