Abstract
Abstract. Since the mid-1990s, a series of FES (finite element solution) global ocean tidal atlases has been produced and released with the primary objective to provide altimetry missions with tidal de-aliasing correction at the best possible accuracy. We describe the underlying hydrodynamic and data assimilation design and accuracy assessments for the latest FES2014 release (finalized in early 2016), especially for the altimetry de-aliasing purposes. The FES2014 atlas shows extremely significant improvements compared to the standard FES2004 and (intermediary) FES2012 atlases, in all ocean compartments, especially in shelf and coastal seas, thanks to the unstructured grid flexible resolution, recent progress in the (prior to assimilation) hydrodynamic tidal solutions, and use of ensemble data assimilation technique. Compared to earlier releases, the available tidal constituent's spectrum has been significantly extended, the overall resolution has been augmented, and additional scientific byproducts such as loading and self-attraction, energy diagnostics, or lowest astronomical tides have been derived from the atlas and are available. Compared to the other available global ocean tidal atlases, FES2014 clearly shows improved de-aliasing performance in most of the global ocean areas and has consequently been integrated in satellite altimetry geophysical data records (GDRs) and gravimetric data processing and adopted in recently renewed ITRF standards (International Terrestrial Reference System, 2020). It also provides very accurate open-boundary tidal conditions for regional and coastal modelling.
Highlights
The FES2014 global ocean atlas is the latest release of a 20year effort to improve tidal predictions needed in satellite altimetry de-aliasing
Despite a rigorous theoretical framework, data assimilation relies on strong assumptions in which the choice of the vector norm chosen to build the penalty function is critical
In the perspective of data assimilation using ensembles for the major ocean tides components, the ensemble members have been computed in the FD mode
Summary
The FES2014 global ocean atlas is the latest release of a 20year effort to improve tidal predictions needed in satellite altimetry de-aliasing It is based on the hydrodynamic modelling of tides (Toulouse Unstructured Grid Ocean model, further denoted T-UGOm) coupled to an ensemble data assimilation code (spectral ensemble optimal interpolation, denoted SpEnOI). The FES2014 atlas denomination is quite misleading, as its final version has been delivered in early 2016 This has left time to the project team to precisely assess the FES2014 accuracy and performance in altimetry data de-aliasing correction and to make some final adjustments to guarantee the best possible quality at that time. Complementary to the present publication, some additional information on present and earlier FES atlases and a link to the associated prediction software can be found on the Aviso+ website
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