IFS Documentation front page

I Observations
II Assimilation
III Dynamics
IV Physics
V Ensemble
VI Technical
VII Waves

4.5 The IFS model

On 2nd March 1994, the model code described above was replaced in operations by the IFS (`Integrated Forecasting System) model, developed in collaboration with Météo-France (where it is known as ARPEGE; see Courtier et al. (1991) for an account of this project). The new code includes all the features required for three- and four-dimensional variational data assimilation (Thépaut and Courtier, 1991; Rabier and Courtier, 1992), and for determining optimal unstable perturbations for ensemble prediction (Buizza et al. 1993). The computational structure of the forecast model component of the system is similar to that described above but includes further improvements in efficiency, notably the matrix-multiplication treatment of the Legendre transforms in the first scan as well as the third scan (see Subsection 4.1 above), and the option to combine several latitude rows together (for example near the poles of the reduced grid) resulting in longer vectors.