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WorkingGroups/TAM/ReferenceManual/Introduction – NEMO
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NEMO-TAM Reference Manual

1 - Introduction


Abstract

The development of the tangent linear and adjoint models (TAM in the following) of the dynamical core of the NEMO ocean engine (NEMOTAM) is a key objective of the VODA ANR project. TAM are widely used for variational assimilation applications, but they are also powerful tools for the analysis of physical processes, since they can be used for sensitivity analysis, parameter identification and for the computation of characteristic vectors (singular vectors, Liapunov vectors, etc.).

In the framework of VODA, a work package has been set-up in order to develop a comprehensive NEMOTAM package, and to define an effective long-term development strategy for ensuring synchronisation of NEMOTAM with future NEMO releases. This is a heavy task, but it is worth the effort since NEMOTAM will benefit all NEMO users for the wide range of applications described above.

Ideally, this strategy should be defined to allow NEMOTAM to adapt to future NEMO developments as quickly and as efficiently as possible, so that new releases of NEMOTAM can be made soon after new releases of NEMO. This will require careful coordination between the main development teams of NEMO, NEMOTAM and possibly NEMOVAR (INRIA, NEMO Team, CERFACS, ECMWF).

Introduction

The NEMO ocean engine [Madec 2008] was previously known as the OPA model [Madec et al. 1998]. It used to have a TAM (called OPATAM), fully hand-coded and maintained mainly by A. Weaver. OPATAM was initially developed for a Pacific ocean configuration, and targeted at variational data assimilation applications in the framework of OPAVAR [Weaver et al. 2003, 2005]. OPATAM/OPAVAR were extended to other regional basins (Mediterranean sea [Rémy 1999], North Atlantic 1/3° [Forget et al. 2008], South Atlantic 1° ), to the global ocean (ORCA 2° [Daget et al. 2009]), and were used for methodological studies such as control of the 3D model error [Vidard 2001], control of the surface forcing and open boundary conditions [Deltel 2002, Vossepoel et al. 2003]. OPATAM was also used for sensitivity studies [Sévellec et al. 2008], singular vectors [Moore et al. 2003, Sévellec et al. 2009], etc. For several reasons, mainly because of lack of workforce, OPATAM, OPAVAR and related developments were not included in the standard release of OPA. As a consequence, synchronisation of OPATAM with OPA’s releases could not be achieved on a regular basis, and all developments were on individual branches, without feedback to the OPATAM/OPAVAR system. The pool of potential users was reduced consequently. It is important not to repeat this error in the future, so as to ensure that NEMOTAM become a widely used community tool.