Section: New Results
Data Assimilation for Ocean Models
Development of a Variational Data Assimilation System for OPA9/NEMO
Participants : Arthur Vidard, Franck Vigilant, Claire Chauvin, Bénédicte Lemieux-Dudon, Pierre-Antoine Bouttier.
A new version of the French ocean model OPA (Ocean PArallèle), ocean component of the NEMO (Nucleus for European Modelling of the Ocean) framework was released in 2005. For the previous version of the OPA model (8.2) a variational data assimilation system, OPAVAR, was developed mainly by A. Weaver at CERFACS. However the OPA 9 model has been completely rewritten in Fortran 90 and the code structure is significantly different from the previous versions, making it quite difficult to update OPAVAR .
Since a large community is interested in variational data assimilation with OPA9, we built a working group (coordinated by A. Vidard) in order to bring together various OPAVAR user-groups with diverse scientific interests (ranging from singular vector and sensitivity studies to specific issues in variational assimilation), and to get technical and scientific support from Inria Sophia (Automatic adjoint derivation, TROPICS project-team) and ECMWF (Parallelization). This project aimed at avoiding duplication of effort, and at developing a common NEMOVAR platform. It has led to the creation of the VODA (Variational Ocean Data Assimilation for multi scales applications) ANR project
The project is now well advanced, both 3D and 4D variational methods are implemented, a fully parallel version of NEMOTAM (Tangent and Adjoint Model for NEMO) is now available and will soon be included in the NEMO standard version.
As part of VODA, we are also working toward a NEMO-ASSIM framework in collaboration with LEGI, by including other kind of data assimilation methods (e.g. SEEK filter) in the NEMOVAR framework.
apart from the VODA ANR project, the NEMOVAR working group gets additional financial support by LEFE-Assimilation and the Mercator National Programs.
Assimilation of Lagrangian Data
Participants : Claire Chauvin, Arthur Vidard, Maëlle Nodet.
This work is motivated by the Argo program, which aims at deploying a network of 3000 profiling floats over the world ocean. These profilers drift at a typical depth of 1500m, and perform a vertical profile of temperature and salinity measurements every ten days. Their position is known every ten days, which gives a set of lagrangian data. We have developed a variational method in order to assimilate such data, a paper presenting the grounding theory of this method has been published in [16] . Twin experiments were performed within the OPAVAR model, in an idealized configuration.
The next step is to implement this method into the state-of-the-art realistic ocean model NEMO and its 4D-Var extension NEMOVAR, as presented in [29] .
This project is currently under development and is granted by ANR-VODA.
