Extensive validation and diagnostics for the tangent and adjoint models - Application to NEMO

The Tangent and Adjoint Models (TAM) are very effective tools for ocean data assimilation, sensitivity and stability analysis, and uncertainty propagations. However the development of such tools can be tedious and error prone and validation is therefore an important aspect. Fortunately there exist many ways to evaluate the validity of the TAM, from very basic to sophisticated. Some of these validation tools can also be used to diagnose the degree of non-linearity of the direct model. We will present a review of existing diagnostics for TAM and propose several new ones, and apply them to the recently released TAM for the European ocean community model NEMO.