OCEANIC ANGULAR-MOMENTUM AND TORQUES IN A GENERAL-CIRCULATION MODEL

The ocean's angular momentum (M) and torques about the polar axis are analyzed using output from the global, eddy-resolving model of Semtner and Chervin. Seasonal variability in M is dominated by the annual cyc le, whose magnitude appears capable of helping explain the residual in the solid earth-atmosphere annual momentum budget. Planetary (M(Omega )) and relative (M(r)) ocean angular momentum components have comparab le seasonal amplitudes. Most of the mean signal in M(r) results from f lows in the Antarctic Circumpolar Current region, but flows as far nor th as approximately 30 degrees S are needed to explain the seasonal cy cle. Locally, the strongest variability in relative angular momentum i s found in the Tropics at all depths, a manifestation of the zonal, re circulating character of the tropical circulation. The time rate of ch ange of M is very small compared to the applied wind torque. Calculati on of bottom pressure torques using the geostrophic relation reveals a dominant balance between them and the surface wind torques in the mod el, implying a rapid transfer of angular momentum between the atmosphe re and the solid earth through the ocean. The torque balance holds for latitudes totally blocked by continental boundaries as well as for la titudes that are only partially blocked (e.g., Drake Passage), suggest ing the same angular momentum transfer mechanism for dosed basin and A ntarctic Circumpolar Current regions. Implications of the results for future ocean modeling efforts are discussed.