12.06.10: Horizontal structure of potential density in the 1/30th and 1/10th deg. OFES simulation

Figs. 1 to 3 show the horizontal distribution of potential density σ at three different depths in the snapshot of the 1/30th-deg. OFES simulation. At 50 m, we can see that horizontal stirring is an important mechanism. It is less clear at 100 and 150 m. At these depths, σ has larger horizontal scale (in accord with the Surface Quasi-geostrophy dynamics; see Lapeyre and Klein 2006).

Figure 1: σ at 52.5m depth in the snapshot of the 1/30th deg. OFES simulation

Figure 2: σ at 102.5m depth in the snapshot of the 1/30th deg. OFES simulation

Figure 3: σ at 151.8m depth in the snapshot of the 1/30th deg. OFES simulation

Is the stirring less apparent at depths because 1) the north-south constrast in σ is weaker, 2) the stirring is weaker because the horizontal flow is weaker, 3) diffusion is relatively larger than at the surface, or 4) a combination of all?

Fig. 4 shows the distribution of salinity at 150 m. We can see that horizontal stirring is still important. So the weaker constrast in σ and the larger diffusion (why the diffusion is larger at 150 than at 50 m?) may explain the apparently weaker role of stirring in σ.

Figure 4: Salinity at 151.8m depth in the snapshot of the 1/30th deg. OFES simulation

We note also that the pattern in σ is similar in the 1/10th-deg. OFES simulation (Figs. 5 to 7). The absence of submesoscale features at 100 and 150 m in both simulations may be inconsistent with the observations at station ALOHA and ARGO floats.

Figure 5: σ at 54.0m depth in the snapshot of the 1/10th deg. OFES simulation

Figure 6: σ at 107.8m depth in the snapshot of the 1/10th deg. OFES simulation

Figure 7: σ at 148.4m depth in the snapshot of the 1/10th deg. OFES simulation