A network-based characterization of eddy activity via the META-Networks dataset from multi-satellite altimetry

Mesoscale eddies are ubiquitous features of the global ocean. They can trap and transport water over large distances and therefore play a key role in regulating the ocean’s energy, heat and biogeochemical cycles. Furthermore, they impact the transport of surface tracers and therefore have an important influence in regulating the geographical distribution of surface tracers and ecological niches. Global observations of the large-scale mesoscale circulation (i.e. scales > 100 km) are provided daily by the sea surface heights maps obtained from the merging of the along-track measurements acquired by the current constellation of satellite altimeters. Due to large spatial and temporal extent of such datasets, mesoscale studies based on satellite altimetry required the development of automated methods to identify and track individual mesoscale eddies.

The META-Networks (Mesoscale Eddy Trajectories Atlas – Networks) is a new eddy dataset based on the fields of absolute dynamic topography reconstructed using the new Multiscale Interpolation gridding (MIOST) from 1993 to present. Like other existing datasets, META-Networks provides mesoscale eddy characteristics and tracks over the global ocean. The tracks are reconstructed by combining together the individual eddies detected from sea level elevation using the Py-Eddy-Tracker algorithm (PET) described by Mason et al., 2014, and available here https://github.com/AntSimi/py-eddy-tracker.

A key additional feature of META-network is that individual tracks are combined together in a series of eddy-networks which takes into account eddy-eddy interactions at the beginning and end of each track. Such interactions are identified via eddy overlapping from individual tracks, and the tracks are associated in the same network if the overlap ratio (defined as the intersection of the area of the two eddies divided by the union of their areas) is larger than a given threshold. Such network representation enables the analysis of eddy properties not only during individual along-track evolution, but also at times of merging and splitting interactions with other eddies, providing an additional point of view for the characterization of mesoscale activity in the global ocean.

Here we present a global overview of the identified eddy networks. Each network is characterized based on its spatial and temporal extent and as well as on the statistical properties (duration, size, intensity etc.) of the individual eddies that comprise it. Within each network, eddy-eddy interactions are analyzed to highlight the regional and dynamical conditions that favor the occurrence of merging and splitting events. Finally, to qualitatively validate the reconstructed networks and identified synergies, a few examples of synergies with other remotely sensed variables (e.g. ocean color and sea surface temperature) at the time of specific eddy merging and splitting events are also investigated and discussed.