Development of a four-dimensional variational analysis system using the adjoint method at GLA. I - Dynamics

Abstract Recent developments in the field of data assimilation have Pointed to variational analysis (essentially least- squares fitting, of a model solution to observed data) using the adjoint method as a new direction that holds the potential of major improvements over the current optimal interpolation (0I) method. The shortcomings of the existing OI analysis method, such as the questionable basic assumptions underlying some of the statistical formulations and the linearity between the analysis and the observation, do not exist in variational analysis. Moreover, variational analysis, by fitting a model solution to data, has the potential of avoiding the long-standing spinup problem in numerical weather prediction. Finally, when the resulting analysis is used as the initial condition for forecasting, since initialization will be performed internally to the analysis procedure, no separate initialization procedure is required before forecast starts. This paper describes the initial effort in the development...