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Test of the eSQG routine in OFES for the North Atlantic

Conclusion

I tested the eSQG routine in a region where the eSQG has been shown to be successful in predicting the relative vorticity from sea surface height (SSH; Isern-Fontanet et al. 2008). I also test how the eSQG routine predicts vertical velocity (w). The correlation in space between the relative vorticity predicted by eSQG and the model output is on average over 2004 0.85 near the surface, decreasing monotonically to 0.5 at 1000 m. The correlation in w is on average 0.2 with values reaching 0.6 at some times and depths. This is encouraging given that we are dealing with snapshot of vertical velocity that contains inertial motions, not predicted by eSQG. The eSQG succeeds, furthermore, to predict the amplitude and spatial pattern of the variability of w, associated with the Gulf Stream that flows to the north of the domain.

Results

After several tries, the best and easiest method is o have no detrend, no taper but to make the field doubly-periodic, as in Isern-Fontanet et al. (2008). The time series of the correlation in space at every depth between the relative vorticity and w predicted by eSQG and the model outputs is shown in Fig. 1. The correlation in relative vorticity stays relatively constant in time, with high values approaching 0.8-0.9 and decreasing monotonically to 0.5 at 1000 m. The correlation in w is, however, much more variable, with values ranging from -0.28 to 0.63. The highest values are obtained for some sporadic events, around 1000 m. For one particular event, the relative vorticity and w obtained from eSQG are compared to the model outputs (Figs. 2 and 3). The comparison in relative vorticity is good, that in w is less satisfactory. The eSQG method, however, succeeds to predict well the amplitude and structure of the variability in w (Fig. 4).

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Figure 1: Correlation in space at every depth between the relative vorticity (upper) and w (lower) predicted by eSQG and the model outputs over the domain 64W-58W and 29N-36N, during 2004 in OFES. Computed with RESEARCH/PROJECTS/MARINE_BIOLOGY/SUBMESOSCALE_PROCESSES/eSQG/analysis/test_OFES/test_OFES.m.

../../../../../../_images/zeta_output_eSQG_notaper_64W58W_29N36N_604m_2004_OFES.png

Figure 2: Relative vorticity from (a) model output and (b) eSQG at 604 m on May 8th, 2004, the time and depth at which the correlation in w is relatively high (0.62; see Fig. 3).

../../../../../../_images/w_output_eSQG_notaper_64W58W_29N36N_604m_2004_OFES.png

Figure 3: w from (a) model output and (b) eSQG at 604 m on May 8th, 2004, the time and depth at which the correlation in w is relatively high (0.62).

../../../../../../_images/w_std_output_eSQG_notaper_64W58W_29N36N_604m_2004_OFES.png

Figure 4: Standard deviation at 604 from (a) model output and (b) eSQG w.