The Global Observed Ocean Products of the French Mercator project
Gilles Larnicol(1) , stéphanie guinehut(1) , Marie-Helene Rio(1) , Yannice Faugere(1) , and Gael Nicolas(1)
8-10 Rue Hermes,
In the frame of the French Operational Oceanography Mercator project, satellite and in-situ measurements representing the two major complementary key components of the Global Ocean Observing System (GOOS) are combined in order to provide gGlobal oObserved oOcean pProducts at high temporal and spatial resolution. Two kinds of products are generated that both allow to monitor the ocean variability and to validate the MERCATOR Mercator simulations.
First, accurate but sparse in-situ T/S profiles data are merged with high resolution altimeter and SST data in order to reconstruct global instantaneous thermohaline fields from the surface down to 1500 m depth. The merging approach uses first, a multiple linear regression method to derive synthetic T and S profiles from the satellite measurements. These synthetic profiles are then combined with the in-situ T and S profiles using an optimal interpolation method that takes into account analyzed error on the different observations. Twelve years (1993-2004) of 3-D thermohaline fields have been produced with this method and have been first validated and compared with independent in-situ data sets in order to provide an estimation of the performances of the system over the whole ocean. Moreover, the impact of the different observing systems (Argo, SST) has been analysed. The quality of the estimated fields additionally allows us to study the interannual variability of the global ocean heat content as well as of the global mean sea level.
Second, global instantaneous surface currents are derived from a combination of altimeter geostrophic currents, Ekman currents derived from wind-fields and in-situ surface currents derived from drifting buoys. First, a two-parameter model, U= beiθτ, is used to compute the wind-driven circulation (Ekman component). b and θ are estimated with a least square minimization method using drifting buoys and wind stress fields Then, the geostrophic component of the circulation is obtained by combining altimeter currents with the drifting buoys through a multivariate optimal interpolation method. Finally, the Ekman and geostrophic components are added to produce global surface currents products. Five years (1999-2004) of global 1/3° daily surface currents have been produced using QuickSCAT winds, altimeter data (Jason/ENVISAT), and drifting buoys coming from the AOML center. Impact of Ekman component, Mean Dynamic Topography (MDT), and drifting buoys are successively analysed.
Finally, the Global Observed Ocean Products (3D-thermohaline and surface currents fields) have been used as referenced fields for validation studies. Indeed, the comparison between MERCATOR simulations with these observed fields allows us to characterise the differences between observed products and simulations and to quantify the information provided by the model and its dynamic.