Variational data assimilation with moist threshold processes using the NMC spectral model

This paper describes a detailed study of variational 4-D data assimilation including the physical processes of large-scale precipitation and deep cumulus convection. The length of the assimilation window is 6 h, and the data are NMC's operational analyses. A comparison of the minimization behaviour, the computational complexity, the quality of the retrieved initial state, with and without physical processes is presented. The results demonstrate the ability to perform 4-D variational data assimilation with discontinuous physical processes. The experiments are carried out with the NMC global spectral model in a resolution of 18 layers in the vertical and a 40 wave triangular truncation.