An atmospheric general circulation model developed in the Meteorological Research Institute is described. The model has 23 vertical layers from the earth's surface to approximately 70km in the middle mesosphere. It uses the spectral transform method with a rhomboidal 24 truncation. The model includes all major physical processes. It has been run for ten years with climatological sea surface temperatures (SSTs). The model generally simulates the features of the general atmospheric circulation in the troposphere and the stratosphere reasonably well. Some drawbacks exist, however, such as the lack of equatorial quasi-biennial oscillation (QBO). It should be emphasized that the model is successful in simulating the interannual variation in stratospheric circulation in the extratropics without any interannual changes in SSTs or external forcing.
An investigation was conducted of the poleward jet shift appearing in the Southern Hemisphere winter, by means of data simulated by a general circulation model. The poleward jet-shift in the model is found to be well simulated, although the jet in mid-winter exists fairly southward compared with observation. It is conjectured that the poleward jet-shift in the model was preconditioned by the wave breaking of a forerunning Rossby wave with zonal-wavenumber 1, and then it occurred by the breaking of another strong Rossby wave packet with zonal-wavenumber 1 at the jet axis in the upper stratosphere.