Operational Performance of a Regional Numerical Weather Prediction Model

[摘要] The operational performance of the JMA regional numerical weather prediction (NWP) model (6L-FLM) is summarized from operational and modelling aspects.The formulation of the computational model is first described. The finite difference scheme of the model is designed along the idea proposed by Okamura (1975). The orography is taken into account only in a limited way. As to the physical processess in the model atmosphere, the following treatments are introduced: (1) parameterization of transfer process in the boundary layer, (2) parameterization of the ensemble effect of convective activities, (3) condensation, (4) orographic effect, (5) sub-grid scale lateral diffusion. No radiative cooling is considered. Concerning the initialization procedure, combination of the balanced wind and the quasi-geostrophic divergent wind is used as the initial wind.Several examples are shown for particular cases like the cyclone development, the formation of a frontal disturbance and the outbreak of a Siberian high as well as the statistical score and the verification of the precipitation forecast. The model has shown acceptable skill for simulating evolution of the synoptic scale motion, but failed to yield a clear cut pattern of the medium scale disturbance. Nevertheless, convection activities due to the moist instability associated with the smaller scale motion are well controlled in the predicted vertical ρ-velocity field and accumulated rainfall distribution.Remaining problems to be solved in near future are discussed. Among other things, the following items particularly attract our attentions, i.e., (1) minimum predictable scab of the model, (2) adequate simulation of the baroclinic instability, (3) prediction in lower latitudes, (4) specification of the lateral boundary condition, (5) fictitious development of the surface anticyclone, (6) treatment of mountain and (7) improvement of the planetary boundary layer and convection parameterization schemes.It may be concluded that, regardless to these unsolved problems, the 6L-FLM is in general well capable of realistically depicting evolution of the synoptic scale motion and yields useful information to be interpreted to the local weather forecasting by the statistical method such as the Model Output Statistics (MOS).

[学科分类] 大气科学