Simulation of the Air-Mass Transformation Process Using a Numerical Model with the Detailed Boundary Layer Parameterization

Abstract

This paper describes the numerical simulation of the air-mass transformation by a three dimensional model. The model has a relatively high vertical resolution in the lower troposphere to improve the treatment of the vertical turbulent transfer processes in the boundary layer. The physical processes taken account of in the model are: (1) surface exchange of heat, moisture and momentum based on the similarity theory, (2) vertical turbulent transfer of heat, moisture and momentum based on the turbulent closure model of level 2 (Mellor and Yamada, 1974), (3) the parameterization of convection (the moist convective adjustment) and the condensation of moisture, (4) orographic effect, and (5) sub-grid scale lateral diffusion.
The model is applied to the observed meteorological situation under the northwest monsoon over the Sea of Japan. The simulated heat, moisture and momentum budget due to the sub-grid scale processes are discussed. The results are encouraging. However further improvement is required.In particular, the moist convective adjustment causes unrealistically large cooling and too humid stratification near the surface.
Preliminary result of a sensitivity test which is relevant to future improvement and remaining problems are also discussed.