1999 Volume 50 Issue 1 Pages 15-53
A preliminary result of a new atmospheric general circulation model (MRI/JMA98) in the Meteorological Research Institute is described focusing on the seasonal and monthly mean fields. The model is based on the spectral global model, which is operationally used for weather forecasting in the Japan Meteorological Agency. The horizontal resolution is reduced to that of triangular 42 truncation (T42), but the top level is raised up to the mesopause (0.01hPa) with an increase of layers to 45 (L45) layers. A little lower model is also made, the top of which is at 0.4hPa just above the stratopause, with 30 layers (L30). Some physical process schemes are improved. The radiative scheme is replaced for solar and terrestrial radiation to yield sufficient accuracy in the middle atmosphere. The ground hydrology scheme is also updated. Soil layers for temperature are increased from two to three layers, similar to those for water, leading to a rigorous treatment of melting and freezing of water through the consistency between heat and water budgets.
Four- and three-year simulations are made with T42L45 and T42L30 models, respectively, under a climatological sea surface temperature, and both models reproduce reasonably well the general features of the observed atmosphere. Additional runs are performed to investigate the effects of top level position and enhanced horizontal diffusion, and their results are also described.
