Monitoring the mesoscale ocean circulation with multi-satellite altimetric missions: a data-assimilation study
Résumé
The general objective of this work is to assess a variety of multi-satellite altimetric scenarios aimed at monitoring the mesoscale ocean circulation in connection with numerical models and assimilation methods. The approach taken for this work is based on Observing-Systems Simulation Experiments (OSSE). We performed twin assimilation experiments, using a numerical model to generate synthetic data according to the sampling schemes achieved by the satellite constellations under study. An academic model of the Gulf Stream system has been developed, using the OPA primitive-equation model at eddy-resolving resolution with a simplified ocean configuration forced by zonal winds. The sea-surface height data are sampled from the model output, along the ground tracks which in this experiment figure out the TOPEX/Poseidon, Jason-1 and AltiKa satellites flying with 10, 10 and 35 days orbital periods respectively. The SEEK (Singular Evolutive Extended Kalman) filter is implemented to assimilate the altimetric data, using an EOF basis to reduce the error sub-space and a local approximation to improve the impact of along-track measurements. The evolution of the reduced order error covariance matrix is performed dynamically using the OPA model, in order to propagate in time the error statistic produced by the filter. The dynamical and local evolution of the error modes managed to represent a forecasted state that is statistically more coherent with the system state. The results of several assimilation experiments will be discussed by considering a variety of analysis, forecast and persistence diagnostics.
