Tropical Circulation in a Time-Integration of a Global Model of the Atmosphere

Abstract

An analysis is made of the structure and energetics of the tropical circulation which emerged from a numerical time integration of a global circulation model with realistic orography. Near the earth's surface, the general features of the time mean flow field and the location of the inter-tropical convergence zone of the model compare favorably with those of the actual atmosphere. Along the convergence zone or shear line, disturbances with a characteristic scale of 2000–3000 km develop and cause heavy precipitation. They tend to develop in the geographical areas where the formation of actual tropical storms is most probable. In the upper troposphere of the model tropics, disturbances with planetary scale develop and are responsible for the maximum of eddy kinetic energy there. In general, both the kinetic energy of the tropical cyclones and that of the planetary-scale disturbances in the model tropics are chiefly maintained by the conversion of available potential energy generated by the heat of condensation. However, the planetary-scale disturbances in the upper troposphere of the tropics seem to be also affected by various factors such as the interaction with higher latitudes and land–sea contrast. It is noteworthy that these disturbances transport angular momentum across the equator in the upper troposphere and strongly affect the budget of angular momentum in the model tropics.