Up to What Extent Can We Characterize Ocean Eddies Using Present‐Day Gridded Altimetric Products?

The most common methodology used to detect and characterize mesoscale eddies in the global ocean is to analyze altimetry‐based sea‐level gridded products with an automatic eddy detection and tracking algorithm. However, a careful look at the location of altimetry tracks shows that their separation is often larger than the Rossby radius of deformation. This implies that gridded products based on the information obtained along track would potentially be unable to characterize the mesoscale variability and, in particular, the eddy field. In this study, we analyze up to what extent sea‐level gridded products are able to characterize mesoscale eddies with a special focus on the North Atlantic Ocean and the Mediterranean Sea. In order to perform this task, we have generated synthetic sea level anomaly maps using along‐track data extracted from realistic high‐resolution ocean model simulations and applying an optimal interpolation procedure. Then, we have used an eddy detection and tracking algorithm to the gridded synthetic product and to the original model outputs and compared the characteristics of the resulting eddy fields. Our results suggest that gridded products largely underestimate the density of eddies, capturing only between 6% and 16% of the total number of eddies. The main reason is that the spatial resolution of the gridded products is not enough to capture the small‐scale eddies that are the most abundant. Also, the unresolved structures are aliased into larger structures in the gridded products, so those products show an unrealistic number of large eddies with overestimated amplitudes.