A Spectral Model for the Study of the Atmospheric General Circulation I. Preliminary Long-Term Integration for the Terrestrial Atmosphere

Abstract

A three-level linear-balance model for studies of the general circulation using the spectral method is presented with some preliminary results of time integration of the model for a specified terrestrial atmospheric condition.
The model is, firstly, integrated for 180 model days under a specified condition to obtain a quasi-steady state without eddies, starting from a calm atmosphere. The zonally symmetric state thus obtained is unstable for the disturbance with zonal wavenumber 5 or 6, according to the linear theory of baroclinic instability. Secondly, after adding disturbances with small amplitudes to the above results of zonally symmetric model, the model integration is continued for another 180 model days to obtain a quasi-steady state with including eddies. The baroclinic instability appears to be released around the day 40, and thereafter the near-equilibrium state is obtained. The results are illustrated mainly for the zonal mean field averaged during either the period of the last 100 days or that of release of baroclinic instability (the day 30-50), and for the time evolutions of energy components and energy conversion terms. The results are not necessarily realistic, because somewhat large values are used tentatively for a part of several parameters, such as the vertical eddy mixing coefficient. Nevertheless, reasonable results are obtained and they are consistent under the model assumption.
In order to study extensive problems concerning the general circulation and the climate of the planetary atmospheres, such a numerical model as is simple, economical and easy to handle is useful and worth-while to construct. So far as the preliminary results are concerned, we may say that the present model is one of powerful tools for further studies on the above subjects.