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02.05.13: Zonal average of the zonal Lagrangian mean flow in all simulations

Fig. 1 shows the zonal average of the zonal component of the Lagrangian-mean flow in all simulations. The right panels show the average scaled by the squared rms value of the meridional component (a measure for the squared amplitude of the wave field). Fig. 2 shows a measure of the southern eastward jet, of the southern westward jet and of the central jet plotted against the value of K. The right panels also show the values divided by the squared amplitude of the wave field. We see that the conclusion that needs to be drawn is completely different from what I wrote recently and depends on which value (divided by the squared amplitude of the wave field or not) we are looking at.

If we look at the raw values (left panels of Figs. 1 and 2), the weaker the diffusivity coefficient (K), the stronger the circulation. The jet along 30°N goes from going west at large K values to strongly east at weak K values. That is because with weaker diffusivity, a convergent cross-PV transport is appearing between 9°E and 10°E, as seen, for instance, in the lower panels of Fig. 1 of 02.05.13: Eulerian and Lagrangian mean dissipative term in all simulations. It is this generation of a new circulation (with weaker K) that leads to a weaker cross-PV transport when averaged over the area used in the paper. As Fig. 1 shows, this cancellation is artificial.

If we look at the values scaled by the squared amplitude of the wave field, we see that the strength of the eastward and westward jets increase with increasing K, except for the central jet that goes from eastward to westward with increasing K. The amplitude of all jets do seem to reach a plateau for the largest value of K.

The important conclusion that the transport stays a function of K is still true, however.

Note the north-south asymmetry that appears with the lowest value of K used (0.1e3 m2/s; black lines in the lower panels of Fig. 1).

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Figure 1: Zonal average (between 2.5°E and 7.5°E) of the zonal component of the Lagrangian-mean flow in all simulations. The right panels show the averages divided by the squared amplitude of the wave field.

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Figure 2: A measure of (upper) southern eastward jet, (middle) southern westward jet and (lower) central jet. These measures were obtained by taking the max between 25°N and 28°N for the southern eastward jet, the min between 28°N and 30°N for the southern westward jet and the value at 30°N for the central jet of the components shown in Fig. 1. The right panels show the values obtained divided by the squared amplitude of the wave field.


plotted with plot_UL_zav in RESEARCH/MODELISATION/HIM/studies/PV_and_dissipation/forced_damped_wave/exp15 on the main ipu1 disk.