The South Atlantic Ocean response to local and remote forcings Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/td96k481c

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  • The local and remote sources of variability of the South Atlantic Ocean are investigated using a set of numerical experiments and satellite data. A global, eddy-permitting, numerical simulation is analyzed to investigate the dynamical links between the Antarctic Circumpolar Current (ACC) and the Malvinas Current (MC). The model results indicate that the correlation between the transports of those two currents is degraded by the presence of high-frequency oscillations of the ACC at the Drake Passage. These anomalies, upon reaching the bifurcation point of the ACC do not follow the coast of South America, instead, they follow the part of the transport that flows along the Polar Front, and therefore, never reaches the MC. A distinct oscillation with a period of 150 days is found. The oscillation seems to originate west of the Drake Passage and propagates along both branches of the ACC. It is shown that anomalies of similar period are also found in altimetry data. A Principal Estimator Pattern analysis suggests that the transport of the ACC and the MC are forced by wind stress curl anomalies over the South Pacific Ocean. It also suggests that the wind stress over the Indian sector might also be important to the variability of these two currents. A series of numerical simulations are run to investigate the influence of the winds over the Southern Hemisphere on the circulation of the South Atlantic Ocean. The analysis of the experiments reveals that the ocean anomalies of the South Atlantic Ocean forced by the local winds ('local' refers to the winds over the South Atlantic Ocean) are restricted to the region north of the Polar Front. On the western boundary, there is a strong response of the Brazil Current (BC) to the local forcing, but the MC is not affected by it. The remotely forced sea surface height (SSH) anomalies that influence the variability of the South Atlantic Ocean are characterized by two SSH maxima over the `hot spots' of the Southern Ocean: the abyssal, resonant modes over the Australian-Antarctic Abyssal Plain and the Bellingshausen Abyssal Plain. These remote modes have a small effect on the variability of the BC. However, they have a strong influence on the variability of the MC. Lastly, connections between transport fluctuations of the Agulhas Current (AC) and the winds over the South Indian and neighboring basins are investigated. The AC does not show any response to wind oscillations over the South Pacific Ocean. This result, however, is not conclusive due to the lack of the Indonesian through flow in the numerical experiments. The contribution of the winds over the South Atlantic Ocean is restricted to the annual cycle of the AC. The winds over the South Indian Ocean seem to be responsible for the interannual variability of the AC and the remaining part of the annual cycle.
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