Controlling the large-scale ocean circulation using a multivariate 3D-Var approach: the complementary role of altimetry and in situ measurements.
Elisabeth Remy(1) , Anthony Weaver(2) , and Nicolas Daget(2)
Parc Technologique du canal,
(2) CERFACS, 31 avenue Gustave Coriolis, 31000 Toulouse, France
The Mercator-Ocean operational systems routinely assimilate in situ and altimetry measurements using an optimal interpolation scheme to estimate initial conditions for two-week ocean state predictions. More advanced assimilation methods are under development in collaboration with external research groups: one of them is the variational approach. In this presentation we explore the ability of a 3D-Var version of OPAVAR, developed at CERFACS, to constrain the global large-scale ocean circulation by assimilating in situ and remote-sensing observations. The experimental design is based on the framework defined in the European ENACT project. Reanalysis experiments for the period 1993-2001 will be described. The experiments are performed with a 2-degree global ocean model, the ORCA2 configuration of OPA. The first one assimilates only in situ temperature and salinity data from the ENACT quality-controlled data-set; the second experiment assimilates only sea-level anomalies from the CLS data-base; and the third experiment assimilates both data-sets. Those simulations are analysed and compared with a free-model run. The relative impact of the different types of observations to constrain the model dynamics and water masses will be investigated. Particular attention will be paid to the large-scale surface and subsurface circulation, its mean and variability on seasonal-to-interannual time-scales. The problem of the MSSH will also be addressed.