Adjustment of an oceanic circumpolar current on different timescales

• Main Author: Maurer-Song, K
• Other Authors: Marshall, D, Maddison, J
• Format: Thesis
• Language: English
• Published: 2024
• Subjects: Physics; Physical oceanography; Antarc*; Antarctic
• Online Access: https://doi.org/10.5287/ora-kokqq2g0o; https://ora.ox.ac.uk/objects/uuid:60732556-df6b-432f-ace8-3b5b86d47b6e

The Antarctic Circumpolar Current (ACC) disproportionately and increasingly affects global anthropogenic climate change. Making observations in this region has been historically difficult so models play a vital role. Even though these models are often times highly idealised circumpolar channel configurations, they are used to understand processes and as test beds for the dynamics of this region. For instance, the equilibrated volume transport of this region is relatively insensitive to changes in the mean surface wind stress forcing: this is known as eddy saturation and is a key feature of ACC dynamics. Another active area of research centres around methods of eddy parameterisation. Eddy parameterisation is used to represent the effects of the mesoscale eddy field in coarser resolution models, such as those used for climate projections. GEOMETRIC is one such parameterisation that succeeds in capturing some unique aspects of circumpolar flow, such as eddy saturation. This thesis investigates the response of a circumpolar current to wind stress perturbations across a variety of timescales. A hierarchy of models--from a dynamical system to an eddy resolving three-dimensional model--is used to understand the physical mechanisms behind the adjustment. In much of the literature, eddy saturation applies only to equilibrated transport and is controlled by baroclinic instability. However, it is known that relative to barotropic processes, baroclinic processes do not react rapidly to temporal wind stress changes, hence, the understanding of circumpolar current adjustment is not complete. This thesis details the responses across {models in multiple dimensions} and forcing frequency and concludes that both barotropic and baroclinic mechanisms affect the circumpolar response to wind stress changes. GEOMETRIC is used throughout this thesis and extends prior work completed on its ability to successfully capture eddy saturation. {An array of models with growing complexity is used to "build up" the physics of a circumpolar ...