Angular Momentum Balance Simulated in January and July by the OSU Two-Level Atmospheric General Circulation Model in a Ten-Year Control Simulation

摘要

A new angular momentum balance has been formulated and applied to the diagnosis of the vertically-integrated January and July angular momentum balances of a ten-year control run of the OSU two-level atmospheric general circulation model (AGCM). The technical improvements over the earlier formulation by Kim and Grady (1980, 1982) are enumerated, with the greatest differences between the results of the two formulations appearing in the global distributions of the horizontal flux convergence of relative angular momentum by the transient component of the circulation and in the distribution of the July pressure-gradient torque. Comparisons are drawn between the simulated angular momentum balance and the balance inferred from observations by Oort and Peixoto (1983). Several features of the globally- and hemispherically-averaged angular momentum balance are discussed. The pressure-gradient and surface frictional torques provide the chief sink and source, respectively, of angular momentum. Both torques are shown to be 2 to 3 times greater in the Northern Hemisphere than during the corresponding season in the Southern Hemisphere, and in both January and July they balance in such a way as to require a net horizontal convergence of both relative and absolute angular momentum into the winter hemisphere. The northen hemisphere relative angular momentum density is shown to be five times greater in January than in July, while the averaged angular momentum fluxes during the northern hemisphere summer are very small. The net poleward flux of relative angular momentum in the Southern Hemisphere is accomplished primarily by the transient component of the circulation; both the standing and transient components transport momentum in the same direction, while in the Northern Hemisphere it is accomplished primarily by the standing component with the standing and transient components transporting momentum in opposite directions. 13 refs., 15 figs. (ERA citation 10:045077)