Intellectual Merit: This project aims to study the short-time scale adjustment of the Antarctic Circumpolar Current (ACC) to rapid and localized changes in wind forcing. The ACC is known to respond coherently and rapidly to changes in wind forcing. This study will test the hypothesis that this fast response of the Southern Ocean is governed by normal modes, as is thought to be the case in the subtropical basins. The Southern Ocean is unlike its subtropical counterparts in many aspects that are likely to affect the adjustment process; the spatial (especially zonal) length scale is much larger than for subtropical basins, prominent bathymetric features like ridges are present in the Southern Ocean, and in the latitude range of the Drake Passage, no meridional boundaries exist to accommodate a boundary current. Furthermore, the ACC comprises a system of strong eastward jets that may affect the Rossby basin modes. The project will address the following questions: i) Is the adjustment of the Southern Ocean governed by basin modes? ii) To what extent does the strong flow of the ACC modify the basin modes and the adjustment process? iii) What is the role of the bathymetric features in shaping the Southern Ocean response to wind fluctuations? iv) To what extent is the Drake Passage a barrier for barotropic waves and normal modes? v) What perturbations in wind stress will lead to the most energetic disturbances?
Broader Impacts: A better description of the variability in the Southern Ocean has consequences for a large range of fields, including weather prediction, wave-height prediction, navigation, and fishery. In addition, understanding what governs the path and strength of the ACC and their variability facilitates the interpretation of oceanographic observations from drifters, pressure gauges, and remote sensing, and may ultimately increase their accuracy. From another perspective, this project will advance the development of implicit ocean models. These are relatively new tools which provide a more fundamental understanding of ocean dynamics than conventional models. The project will further the career development of a post-doc working on a self-directed project. In the end, the community may have been offered a clear insight into the way the ACC adjusts to rapidly varying winds. This may lead to a better appreciation of its role in past climates, and, ultimately, it may increase the ability to anticipate on its response to future climate changes.
