Diapyncal mixing in the Southern Ocean (SO) plays a vital role in controlling the global over- turning circulation that redistributes heat, freshwater, and dissolved greenhouse gases throughout the world's oceans. The rate at which water masses are imported, transformed, and exported to the rest of the world are controlled by the Southern Ocean Meridional Overturning Circulation and several interior dynamics. However, the ACC represents the only oceanic instance of a zonally unbounded flow, and is therefore not subject to Sverdrup dynamics. Instead, all meridional transport of heat, freshwater, dissolved gases, and nutrients is accomplished through meridional flows. Many previous models of ACC dynamics have assumed that all water modification has occured at the surface while the surface water below has flowed northward or southward along isopycnal surfaces. However, a series of recent studies in the Southern Ocean has suggested that the diabatic fluxes from propagating internal-waves are too large to be ignored.
In this study, a researcher at the University of California-San Diego Scripps Institution of Oceanography will investigate the relative importance of breaking energetic internal waves on the net meridional circulation in a zonally unbounded flow such as the ACC through a series of idealized numerical experiments. The experiments will impose an upward propagating field of internal waves, consistent with various models of wave generation, onto a realistic mean zonal flow and geostrophic eddy field. Based on previous and preliminary work, the waves will break due to a combination of intrinsic nonlinear dynamics, absorption into critical layers, and interaction with eddy vorticity. The rate of energy loss from propagating internal waves will determine the vertical structure of wave-breaking and the depth of associated meridional stresses and water mass modification.
Broader Impacts: The results from this work will not only lead to a better understanding of the Meridional Overturning Circulation of the Southern Ocean but also improve the communities conceptual understanding and the accuracy of operational climate models. The circulation of the Southern Ocean plays an extremely important role in the earth's climate by regulating the global movement and storage of heat, freshwater, dissolved greenhouse gases, and biologically essential nutrients. Current global scale models may suffer from not appropriately including the diabatic forcing from breaking internal-waves in Southern Ocean dynamics. A dynamical understanding of the resultant geography of mixing is required for accurate understanding and modeling of the large-scale circulation in past, present and future climates. The immediate goal of this project is to develop a dynamical understanding that will allow appropriate parameterization of these effects to improve our conceptual understanding and the accuracy of operational climate models.
