Linearized Physics for Data Assimilation at ECMWF - Data Assimilation for Atmospheric, Oceanic and Hydrologic Applications - page 278

Even though there is some hope that future configurations of data assimilation
based on weak-constraint 4D-Var might provide some ways to slightly relax the
linearity constraint in time, it is paramount that non-linear model developers always
remember that 4D-Var can only deliver good analyses if the linearity assumption
remains valid over the entire assimilation window.
Acknowledgements The authors would like to thank Peter Bauer, Anton Beljaars and Jean-Noel
Thepaut for their useful reviews of this paper. The anonymous reviewer is also acknowledged for
reviewing the manuscript.
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