Fine Resolution Altimetry Data for a Regional Application in the Bay of Biscay

Abstract

Eddy properties in the Bay of Biscay are studied from 15 years of reprocessed along-track altimeter data using a wavelet-based analysis. Associated spatial scales vary from ∼60 km in the inner bay to 130 km offshore, with amplitudes also increasing offshore. These characteristics are not correctly represented in standard gridded products, which are too smooth. Compared to observed along-track data, geostrophic currents and eddy kinetic energy estimated from standard gridded maps are too weak by a factor of 33% and 50%, respectively. A new mapping approach is proposed to better resolve the local mesoscale variability. It uses the larger wavelengths of the standard gridded maps as a first guess and adds an increment based on the short scale signals of the along-track data. First results show coherent fine scale signals, consistent with the information provided by MODIS imagery.

Keywords:

• Altimetry
• mesoscale dynamics
• Bay of Biscay
• spectral analysis
• wavelet analysis
• objective analysis

Acknowledgements

The authors warmly thank members of the CTOH and X-TRACK teams at LEGOS, Toulouse, for their contribution to this paper by providing the multisource data sets and their expertise. Computing facilities were made available by the LEGOS and the Pole d’Océanographie Côtière via the Laboratory of Aérologie in Toulouse. Fruitful discussions on altimeter mapping were appreciated with colleagues in CLS and the OSTST Science team. The project was supported by the French TOSCA program via the CNES, by a French DGA Ph.D. grant (from Direction Générale de l’Armement) and is a contribution to the MyOcean Sealevel project. Finally, we thank the anonymous reviewers who helped to improve the quality of our manuscript.