11.10.12: Eddy trajectory from AVISO SSH and HYCOM SSH

I have calculated the past and future trajectory of the eddy observed during BIOLINCS from the data-assimilating global HYCOM model and I compare it to that obtained from AVISO SSH (Fig. 1).

The past trajectories are in agreement up to March 2011 (around 152°W ad 26°N). After that, the eddy lost its SSH signature in the model SSH while it is still seen in AVISO SSH. In the model, the sudden absence of the SSH signature obliges the search algorithm to look for another eddy in the surrounding area. This explains why the model’s trajectory after March 2011 expands quickly to the east. The accumulation of the dots in the southeast corner is another artifact and is due to the fact the model trajectory has reached the boundaries of the model SSH that I have downloaded.

The future trajectories diverge quickly. That is because there are two close anticyclonic eddies and the search algorithm follows a different eddy in each case. Visually, I would think the trajectory obtained from the model is the right one. The accumulation of dots in the southwest corner is also due to the fact that the model’s trajectory has reached the boundaries of the downloaded model SSH.

There is not much to conclude. It is pleasing to see that the two past trajectories agree, at least until March 2011. But this should not be a big surprise given that the model assimilates AVISO SSH.

Figure 1: Past and future trajectory of the eddy observed during BIOLINCS: deduced from AVISO SSH (blue) and from the global HYCOM SSH (red) that assimilates SSH. The vertical and horizontal dashed lines indicate the position of the eddy on Sept. 19, 2011, during BIOLINCS.

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Trajectories were computed with SSH_analysis.m and HYCOM_global_analysis_bis.m and the plot was made with plot_SSH_AVISO_SSH_HYCOM_global_eddy_traj.m. All are in RESEARCH/PROJECTS/MARINE_BIOLOGY/SUBMESOSCALE_PROCESSES/BIOLINCS on the main disk.