Abstract
A low resolution spectral general circulation model has been developed for two aims. The first is to use the model as a tool to study the mechanisms of the atmospheric variations of longer terms than 10 days. The second is to perform preliminary studies on the dynamical long-range forecast. The model adopts primitive equations in which the dependent variables, except the mixing ratio of water vapor, are expressed by spherical harmonic functions with rhomboidal truncation of wavenumber 10. It has 10 layers including the lower stratosphere. To drive and maintain the general circulation of the model atmosphere, radiation, convection, turbulent vertical mixing in the planetary boundary layer, ground thermodynamics and hydrology are all incorporated by their widely used parameterization schemes.
This paper describes the model performance by showing calculated monthly fields for January and July. These are obtained from the last 5 years results of simulated 6.5-year seasonal changes.
We show that the major large-scale phenomena of the real atmosphere have been successfully simulated by the model. For example the stratospheric polar night jet and tropospheric subtropical jet are clearly separated in the winter hemisphere. Zonal mean and geographical distribution of monthly mean fields of wind, temperature and other parameters are realistic, although the model includes some defects such as the broader ITCZ and weakened Hadley circulation. In the stratosphere of the winter Northern Hemisphere, geopotential height and temperature structures well resemble the observed ones in both amplitude and phase. Stationary wave structures of geopotential height throughout the troposphere and stratosphere are also similar to the observed ones in the winter Northern Hemisphere, but not in the winter Southern Hemisphere.
