Fifteen Years of Altimetry and Satellite Data: Benefits for Mercator-ocean Operational Forecasting System
Nicolas Ferry(1) , Benoit Tranchant(1) , Charles-Emmanuel Testut(1) , Elisabeth Remy(1) , Marie Drevillon(1) , Eric Greiner(1) , Mounir Benkiran(1) , Jean-Michel Lellouche(1) , and Pierre Brasseur(2)
8-10 rue Hermes,
31520 RAMONVILLE ST AGNE,
(2) LEGI, BP53, 38041 Grenoble Cedex 9, France
Altimetry played a key role in the emergence of operational ocean forecasting centres such as Mercator-Ocean in France. The global synoptic data coverage and the very high measurement accuracy of Topex-Poseidon in the early nineties was one of the most important factors that pushed to set up the French operational oceanographic centre.
Mercator has developed a series of assimilation techniques in order to optimally combine observations (SLA, SST, in situ T&S profiles) with ocean model simulations. Historically, the first method used (called SAM1) was intended to specifically assimilate sea level anomaly (SLA) data. It was based on an optimal interpolation (OI) analysis associated to the Cooper & Haines (1996) lifting / lowering of isopycnals. The second system to become operational was designed to take advantage from both in situ and remotely sensed (SLA, SST) data through fully multi variate assimilation (also based on an OI approach). Besides these operational systems, Mercator is developing the next generation of multivariate assimilation system, referred to as SAM2, based on Reduced Order Kalman Filters using 3D multivariate modal decomposition of the forecast error covariance. The use of 3D modal representation for the error statistics is intended to improve analyses in highly inhomogeneous and anisotropic regions of the ocean. Lastly, advanced data assimilation techniques such as 3D variational assimilation methods are investigated.
We shall review how altimetric data is assimilated in Mercator analysis systems and how SLA impacts the ocean state estimation. In particular, we focus on the increasing capability of the systems to correctly analyse along track altimetry data. Results from Mercator operational systems as well as from global and regional reanalyses are presented.