THE BAROCLINIC PLANETARY MODES IN DEEP AND SHALLOW SPHERICAL ATMOSPHERIC MODELS

The growth rate, phase speed and the spatial structure of the growing planetary and synoptic waves in winter and summer zonal mean flows have been investigated by the eigenvalue-eigenfunction technique based on a hemispheric and a global model including the troposphere-stratosphere-mesosphere (0-80km). The results show that the winter basic flows are able to generate three types of growing waves:the quasistationary planetary Green modes (wavenumber m=1-2),the deep Charney modes (m=3-4) and the tropospheric propagating Charney modes (m=5-9).In the summer basic flow, 2 types of growing waves exist:the westward propagating waves in the mesosphere (m=1-4) and the eastward propagating waves in the troposphere (m=5-7).The results compare with observation favorably, suggesting that a mechanism of dynamic instability of a deep atmosphere may be responsible for the observed transient planetary waves. By comparison between the results of the deep model and a few shallow models, it is concluded that a numerical model of planetary waves should at least extend to the stratopause. The traditional tropospheric models woule seriously distort structures and phase speeds of the planetary waves.