Advanced data assimilation methods are being developed for operational ocean monitoring and prediction systems, with a view to assimilating satellite observations such as altimetry, sea-surface temperature and ocean color into high-resolution models of the ocean circulations and marine ecosystems. The prototype of an operational North Atlantic forecasting system is currently in development. This paper provides an overview of the most recent results obtained with the TOPEX/POSEIDON Science Working Team, and further develops our plans for the Jason-1 mission.
Satellite observations provide a unique opportunity to monitor the ocean evolution in real time, accurately, at the global scale, and with high resolution. As only the properties of the sea-surface can be observed from space, data assimilation systems are needed to improve the consistency between satellite data and model simulations, to dynamically extrapolate and interpolate measurements scattered in space/time, and to better exploit the results of observation programs like Jason-1. The general objective of this project is to implement and validate innovative methodologies for the assimilation of the Jason-1 altimeter data into ocean and ecosystem models in order to contribute to the development of operational oceanography for programs such as MERCATOR and GODAE and related components (CLIVAR, GOOS, GCOS, etc.). Altimeter data from the Jason-1 satellite will be the primary source of observations in conjunction with TOPEX/POSEIDON and ERS satellites, but particular attention will also be paid to other data types, including in situ observations from Argo and their complementarity with satellite altimetry.The scientific work plan is based on a two-track approach: (i) the development of advanced methodologies for data assimilation, and (ii) their application within pre-operational systems.
A variety of advanced data assimilation and numerical methods are being developed by this project, including:
The validation of these methodologies in a realistic context is achieved using different primitive equation models and ocean configurations, namely: a coupled ocean circulation and marine ecosystem model of the North Atlantic and Nordic Seas (DIADEM and TOPAZ projects of the EU); an eddy-permitting model of the North Atlantic ocean circulation (French MERCATOR project); and, a basin-scale model of the Tropical Pacific ocean circulation.
The SST (sea-surface temperature) and SSH (sea-surface height) observations assimilated in these prototypes consist of 1/4° composite maps of NASA Pathfinder SST data, combined TOPEX/POSEIDON-ERS altimeter data, and SeaWIFS ocean color data. Typical illustrations of three specific applications are given below.
The lessons learned from realistic data assimilation experiments suggest to proceed with iterations between methodological improvements and practical implementations, taking advantage of the Jason-1 mission. Indeed, our recent experience with TOPEX/
At the same time, a continuous effort will be devoted to validating the assimilation systems with independent in situ measurements: up to now, residual misfits with TAO array data in the tropical Pacific, and XBT profiles in the Atlantic Ocean, objectively demonstrate the benefit gained from assimilation, but additional diagnostics are needed to better characterize the strong and weak points of the assimilation systems. The next step will be the simultaneous assimilation of satellite and in situ data, for example from the Argo program, and the evaluation of the complementarity of these various data types.
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Advanced altimeter data assimilation for the development of operational oceanography