[4] Modelrelated issues 1
[42] February 27, 15:0015:20 
The ECMWF weak constraint 4DVar formulation

Yannick Tremolet (ECMWF), Jacky Goddard (ECMWF), Martin Leutbecher (ECMWF), Simon Lang (ECMWF), SarahJane Lock (ECMWF), Patrick Laloyaux (ECMWF) 
Abstract 
In most operational implementations of fourdimensional variational data assimilation, it is assumed that the model used in the data assimilation process is perfect or, at least, that errors in the model can be neglected when compared to other errors in the system. ECMWF has been developing a weakconstraint 4DVar formulation where a modelerror forcing term is explicitly estimated to take into account model imperfections. This problem is very similar in nature to strong constraint 4DVar as it is essentially an initialcondition problem with parameter estimation where the additional parameters represent model error. 
Presentation file:  04_2_P.Laloyaux.pdf 