2008 Volume 86A Pages 121-142
We developed new microphysical schemes that have five and six classes of water substances based on the method of Lin et al. (1983). In the new schemes, ice cloud is simply generated by a saturation-adjustment process. Furthermore, the effect of the wetness of graupel is omitted in the six-class scheme to reduce calculation costs. Because of these simplifications, the newly developed scheme is much less computationally costly than are the commonly used Lin-type schemes. For the validation and comparison of the proposed schemes, squall-line simulations were conducted using the NICAM dynamical core on a stretched icosahedral grid. In this test case, the squall line that was simulated by the schemes with graupel processes developed more quickly than that simulated by the schemes without graupel processes. Despite the simplicity of the processes in the new six-class scheme, its physical performance is similar and its computational performance is higher than those of the established Lin-type scheme.