A numerical test of a global float/altimetry observing system in the ocean

The NOPP Project "Estimating the Circulation and Climate of the Ocean" (ECCO) intends to bring ocean state estimation from its current experimental status to that of a practical and quasi-operational tool for studying large-scale ocean dynamics and examining the ocean's role in climate variability. A subtask of the project is the design of observational strategies, and to identify key regions and methods that are important for monitoring transport variations and climate-relevant signals in the ocean. A first focus will be on profiling, Lagrangian floats, PALACE, that are part of the anticipated global observation system.

For this purpose, an eddy-resolving model has been seeded with artificial floats. The model is based on the MIT model, a highly flexible and parallelized primitive equation model, and covers the global ocean with 1/6 degree horizontal resolution and 30 levels in the vertical. It is driven by wind stress and thermohaline fluxes of the years 1992-1997 that are generated by the ECCO ocean state estimation. A large number of floats, initialized randomly over the global ocean were integrated over the model period.

Questions being investigated include the eddy aliasing effect on the retrieval of large-scale variations from a limited number of float profiles and the effect of the general circulation on the long-term float distribution. In principle clustering could occur, that might be circumvent by smart releasing patterns to maximize the observing capabilities of the floats. It will be tested to what degree float data are capable to measure the ocean circulation in time and space complementary to surface altimetry.