12.13.10: FSLE and WHOTS data

Summary

1. There is little correlation between location of filaments, as estimated from FSLE calculation, and high-frequency events of shallow density contours observed during the first WHOTS deployment.
2. Only in 4 out of 8 cases, we could argue that the event occurs at a location that is near a filament.
3. This low correlation is in part due to the noisy aspect of the time series of filaments. Furthermore, the exact location and timing of the filaments is quite sensitive to the AVISO SSH product making the comparison with the density record more uncertain.
4. However, the frequency of filaments seems to increase in the second part of the record (Spring), coincidentally with the presence of the high-frequency events and low stratification.
5. From a look at the map of filaments, it does not seem that there is more filaments in the second part of the filaments, nor that they propagate faster than in the first half. Thus, it is not clear why their frequency changes.

Results

I show here the calcul of finite-size Lyapunov exponents (FSLE) during the first WHOTS (WH01a) deployment. Fig. 1 shows the time series for the potential density anomaly σ (referenced at the surface) and the time series of λ+ minus λ- at the location of the WHOTS mooring, where λ+ and λ- are the stable and unstable FSLE, respectively. Fig. 2 compares again the FSLE index λ+ minus λ- to a vertical average of mesoscale and submesoscale σ, where the mesoscale is defined as the variability with periods between 1 and 6 months, the submesoscale as the variability with periods less than one month. Figs. 3 to 10 show the map of FSLE for 8 days during which high-frequency (small-scale) events of shallow isopycnal surfaces occur.

Figure 1: (a) Time series of σ during WH01a. (b) Time series of λ+ minus λ- at the location of the WHOTS mooring. The timing of 8 events of shallow isopycnal surfaces are shown by vertical dash lines. The FSLE were computed with manifold_during_WHOTS.m in /home/ipu1/userdirs/francois_moli5/RESEARCH/PROJECTS/MARINE_BIOLOGY/SUBMESOSCALE_PROCESSES/FSLE/analysis/WHOTS. They have been saved in stable_manifold_during_WHOTS_ref.mat and unstable_manifold_during_WHOTS_ref.mat located in /home/gyoji/t1d2/francois/RESEARCH/PROJECTS/MARINE_BIOLOGY/SUBMESOSCALE_PROCESSES/FSLE/analysis/WHOTS.

Figure 2: (a) Time series of σ during WH01a for the mesoscale (1 month < periods < 6 months). (b) Time series of λ+ minus λ- at the location of the WHOTS mooring. (c) Time series of σ during WH01a for the submesoscale (periods < 1 month). See linking_manifold_density_anomaly.m in /home/ipu1/userdirs/francois_moli5/RESEARCH/PROJECTS/MARINE_BIOLOGY/SUBMESOSCALE_PROCESSES/FSLE/analysis/WHOTS.

Figure 3: λ+ minus λ- on Jan. 27, 2005. The black dot shows the location of the WHOTS mooring.

Figure 4: λ+ minus λ- on Feb. 06, 2005. The black dot shows the location of the WHOTS mooring.

Figure 5: λ+ minus λ- on Feb. 16, 2005. The black dot shows the location of the WHOTS mooring.

Figure 6: λ+ minus λ- on Mar. 08, 2005. The black dot shows the location of the WHOTS mooring.

Figure 7: λ+ minus λ- on Apr. 23, 2005. The black dot shows the location of the WHOTS mooring.

Figure 8: λ+ minus λ- on Jun. 06, 2005. The black dot shows the location of the WHOTS mooring.

Figure 9: λ+ minus λ- on Jun. 14, 2005. The black dot shows the location of the WHOTS mooring.

Figure 10: λ+ minus λ- on Jun. 28, 2005. The black dot shows the location of the WHOTS mooring.

In Figs. 11 and 12, we compare λ+ minus λcomputed on Jan. 27, 2005 with the ref and upd AVISO SSH product (all figures before these ones are associated with the ref product). The exact location, shape and amplitude of the filaments can be quite sensitive to the AVISO SSH product used. Given the rather noisy structure of the FSLE, it is difficult to reliably conclude on the relationship between the shallow events and the FSLE.

Figure 11: λ+ minus λ- on Jan. 27, 2005. The black dot shows the location of the WHOTS mooring. The ref AVISO SSH product was used.

Figure 12: λ+ minus λ- on Jan. 27, 2005. The black dot shows the location of the WHOTS mooring. The upd AVISO SSH product was used.