Benoit Legresy (Commonwealth Scientific and Industrial Research Organisation, TAS, Australia); Clothilde Langlais (Commonwealth Scientific and Industrial Research Organisation, TAS, Australia); Paul Sandery (Commonwealth Scientific and Industrial Research Organisation, TAS, Australia); Darren Engwirda (Commonwealth Scientific and Industrial Research Organisation, TAS, Australia); Mike Herzfeld (Commonwealth Scientific and Industrial Research Organisation, TAS, Australia)

The recently launched SWOT (Surface Water and Ocean Topography) satellite provides a new and detailed view of ocean dynamics globally and at scales down to a 15 km wavelength. With the advent of SWOT, there is a critical need to connect high-resolution SSH observations with interior ocean dynamics to estimate key climate-relevant budgets such as vertical heat fluxes. Addressing this challenge involves two complementary strategies: (1) conducting Observing System Simulation Experiments (OSSEs) to develop and validate diagnostic methods and proxies from SSH observations, and (2) assimilating SWOT data into high-resolution ocean models to reconstruct the full 3D ocean circulation. Both approaches require kilometre-scale models capable of capturing realistic ocean dynamics across the full wavenumber spectrum revealed by SWOT.

The SWOT launch has motivated international validation efforts with in-situ campaigns in key dynamic regions. One such validation campaign, the Fine-scale Ocean Currents Under SWOT (FOCUS) voyage, provided a full three-dimensional dataset in an energetic meander of the Antarctic Circumpolar Current (ACC) south of Tasmania, a known hotspot for Eddy Kinetic Energy (EKE) and small-scale motions. This poster presents and validates the FOCUS model, a high-resolution implementation of COMPAS (Coastal Ocean Marine Prediction Across Scales), designed to investigate fine-scale fluxes, conduct OSSEs, and support SWOT data assimilation in the ACC meander. We evaluate the effects of horizontal resolution using a nested grid approach (2.5 km to 800 m), assess the impact of viscosity parameterizations, and explore different vertical discretization to mitigate grid-scale noise. The model’s ability to reproduce a realistic energy cascade is assessed using wavenumber spectra derived from SWOT observations and in situ measurements collected during the FOCUS voyage, including hydrographic and ADCP transects.