The task 2.3 of the WP2 EARISE package has an overarching goal to improve how Argo floats and data are used to study Ocean Boundary Currents (BC).

This deliverable is one component of the strategy toward this goal: to develop an Euro-Argo roadmap with regard to BCs. The other component of the task 2.3 strategy is related to using machine learning to improve Argo synergie with other observing systems in ocean state estimates.

The participants to task 2.3 identified boundary systems of interest and covered by this deliverable:

●  the Gulf Stream (IFREMER),

●  the West Spitsbergen Current and East Greenland Current (BSH, IOPAN),

●  the BCs in the Western Mediterranean region (SOCIB, SU)

●  and the Gulf of Cadiz Current (IPMA)

First we present the scientific rationales for observing these BC systems. Primarily because of their frontal intrinsic structure, BCs are associated with key scientific questions dealing with air-sea and open vs coastal interactions, with profound impact on other components of the climate system (the atmosphere or seaboard areas). This key ingredient, i.e. being a frontal structure, is also the origin of a large turbulent activity, which limits (i) the ability of Argo floats to remain in a BC regions and (ii) the representativity of Argo profiles in this realm of strong eddy field. Hence the need for a dedicated EA strategy with regard to BCs.

Second, a detailed analysis of the historical Argo sampling of these BCs is provided. This analysis is characterised by a very large range of Argo floats configuration parameters as well as very heterogeneous sampling density. Some regions like the Gulf Stream have been fairly well sampled (compared to the core Argo target), while others very poorly, like the Balearic Current and Gulf of Cadiz. It is noted that no specific configuration parameters are being used systematically to optimise observation of the frontal structure and its eddy field.

Last, we provide a first version for a European strategy plan with regard to the Argo extension in WBC and other boundary regions. This initial text lays out, for each BCs, the key European needs, existing capacities and current knowledge about what would be required, as well as the technological advances, to fulfill these needs. Among all these elements we highlight the need for a better informed strategy of numerical experiments based on a Virtual Fleet software to simulate Argo floats that will lead to determine the most appropriate sampling strategies (deployment plans and configuration parameters) in BCs. An initial version of this software has been released in June 2020. Partners are still developing experiments designs. The present strategy plan will thus be revisited in 2022 to take into account the results of these experiments.