Multimission altimetry-derived eddy trajectories in NRT (for Near-Real-Time).

Eddies detected from the multimission altimetry datasets, with location each day giving the type (cyclonic/anticyclonic), speed, radius and associated metadata, for the altimetry period: 01/01/2018 - ongoing with15 days delay.

- Center position (Longitude and latitude of the center of the best fit circle with the contour of maximum circum-average geostrophic speed);

- Amplitude (|SSH(local_extremum) – SSH(outermost_contour)|);

- Speed radius (Radius of the best fit circle with the contour of maximum circum-average geostrophic speed);

- Speed average (Average geostrophic speed of the contour defining the speed radius);

- Speed profile (Profile speed average values from effective contour inwards to smallest inner contour);

- Effective contour (Largest contour of the detected eddy);

- Speed contour (Contour of maximum circum-average geostrophic speed for the detected eddy).

Several versions exist: Delayed time "Twosat" and "Allsat", described on other metadata sheets. Links and cross references below.

The NRT product is based on ”all-satellite” input products, that allows a better sampling of the ocean at a given time. Indeed the focus on short period of time with a best sampling is in the interest of using a NRT product. For the NRT product, the eddy detection is made on ADT maps to avoid a) misinterpreting eddies with a permanent signature and b) that the displacement of large currents creates anomalies similar to eddies.

The algorithm used for this product is derived from the one described in Mason et al. (2014) and further described in Pegliasco et al. (2022).

The mesoscale circulation is defined as a class of energetic phenomena of spatial dimensions ranging from tens to hundreds of kilometers and spanning days to years. The mesoscale structures are mainly generated by currents instabilities, from the ocean large-scale circulation instabilities due to wind or topographic obstacles, creating variability around the ocean’s mean state.

References:

- Mason, E., Pascual, A., McWilliams, J.C., 2014. A New Sea Surface Height–Based Code for Oceanic Mesoscale Eddy Tracking. J. Atmospheric Ocean. Technol. 31, 1181–1188. https://doi.org/10.1175/JTECH-D-14-00019.1

- Pegliasco, C., Delepoulle, A., Mason, E., Morrow, R., Faugère, Y., Dibarboure, G., 2022. META3.1exp: a new global mesoscale eddy trajectory atlas derived from altimetry. Earth Syst. Sci. Data 14, 1087–1107. https://doi.org/10.5194/essd-14-1087-2022

- Visvalingam, M., Whyatt, J.D., 1992. Line generalisation by repeated elimination of the smallest area. Cartogr. Inf. Syst. Res. Group University of Hull.