Abstract
The development of a nine-layer, quasi-geostrophic, highly truncated spectral model of the atmosphere is described. The model is global, extends to 0.05 mb (71 km) with roughly 10-km resolution in the stratosphere, and includes an annual heating cycle. Preliminary integrations without eddies reveal the seasonal variation of a thermally driven circulation.
A model integration was made to simulate the months of December and January without nonzonal forcing, thus being more representative of a Southern Hemisphere winter. The overall features of the atmosphere were well simulated. A midlatitude temperature maximum was produced in the winter mesosphere of the model, which was driven in the manner of the lower stratosphere. With the inclusion of the annual heating cycle, the model successfully reproduced a more intense circulation in January than existed in December. This caused the maximum tropospheric meridional temperature gradient in the winter hemisphere to occur weeks prior to the maximum in the external heating field. A seasonally coupled index cycle in the very long waves was of significance in producing transient upward energy propagation and, as such, may be the source of sudden stratospheric warming events.
Now affiliated with the New Zealand Meteorological Service, Wellington.
