Abstract
Non-linear normal mode initialization (NNMI) proposed by Machenhauer (1977) is applied to the JMA spectral limited area models. The normal modes of the models are constructed using a constant map factor and Coriolis parameter, which was first performed by Briere (1982) for a grid model. The initialization procedure is carried out in spectral space. The NNMI is designed to preserve the prescribed boundary conditions of the model. By introducing a cut-off period, gravity waves with very low frequency are excluded from the procedure.
The initialization using the adiabatic time tendencies successfully reduced the large time tendencies of the gravity wave modes of the first five vertical modes. The changes of the initial states by the NNMI with a short cut-off period of 6 hours were very small, while the NNMI with a longer cut-off period produced larger initial changes in the baroclinic zone. The NNMI eliminated high frequency oscillations in the subsequent forecast.
