Tuesday, June 2nd, 2:00PM
Location: Revelle 4301
PhD Candidate, Scripps Institution of Oceanography, La Jolla, CA
Sources and sinks of momentum in the Southern Ocean State Estimate
We calculate the Southern Ocean momentum balance using the Southern Ocean State Estimate, an eddy-permitting general circulation model that is constrained to six years of satellite, Argo, and other observations. We find that 95 percent of the zonal momentum input via wind stress at the surface is balanced by topographic form stress across ocean ridges, while the remaining 5 percent is balanced via bottom friction and momentum flux divergences at the model boundaries. While the time-mean zonal wind stress field exhibits a relatively uniform spatial distribution, time-mean topographic form stress concentrates at shallow ridges and across the continents that lie within the Antarctic Circumpolar Current (ACC) latitudes -- primarily Kerguelen Plateau, the Macquarie Ridge region, and South America and the Drake Passage fracture zones -- as well as across deep basins separated by basin-scale plains. Topographic form stress can thus be divided into shallow and deep regimes: the shallow regime contributes most of the westward form stress that serves as a momentum sink for the ACC system, while the deep regime consists of strong eastward and westward form stresses that largely cancel in the zonal integral. The time-varying form stress signal, integrated longitudinally and over the ACC latitudes, tracks closely with the wind stress signal integrated over the same domain, suggesting that changes in the integrated wind stress signal are rapidly communicated down to the level of bottom topography.