Observations of sea surface height (SSH) from SWOT have demonstrated remarkable potential for resolving mesoscale and submesoscale ocean features, which are crucial for assessing vertical velocities, a key variable for understanding the transport of heat, carbon, and nutrients between the ocean surface and interior. In the mesoscale-energetic region south of Tasmania, we evaluate the contributions of larger mesoscales (>100km), observable with traditional nadir-looking altimetry, and smaller scales (<100km) uniquely resolved by SWOT. Metrics such as surface geostrophic velocity, strain rate, relative vorticity, and the Okubo-Weiss parameter are derived from MIOST gridded maps and SWOT data, further partitioned into large (>100km) and small (<100km) scale components. While larger scales predominantly influence geostrophic velocity, smaller scales contribute significantly to current stretching and straining, with hotspots showing up to threefold stronger strain and tenfold stronger vorticity than larger scales. These fine scales reveal dynamic phenomena, such as the front jumping near the Macquarie Ridge, obscured in conventional low-resolution products. Initial validation of SWOT’s small-scale observations is performed using high-frequency (~8km) temperature sampling collected between Tasmania and Antarctica in December 2023 during a SURVOSTRAL campaign. SWOT surface structures align with subsurface horizontal temperature gradients. Vertical velocities (w) down to 1000 m, reconstructed using effective surface Quasi-Geostrophic (eSQG) theory, show that SWOT-derived w exhibits twice the RMS compared to nadir altimetry, underscoring SWOT’s capacity to resolve energetic meso- and submesoscale ocean dynamics. Further work is needed to fully harness SWOT’s high-resolution data in gridded products, as current smoothing limits the retention of valuable small-scale information.

We present the first analysis of velocities and pair dispersion derived from high-resolution sea surface height (SSH) from the new Surface Water and Ocean Topography (SWOT) satellite, in an energetic meander of the Antarctic Circumpolar Current (ACC). We introduce a new fitting kernel method to reduce the impact of errors propagating through derivatives to geostrophic velocities and higher-order diagnostics. This method is applied to derive velocities from SWOT data at different length scales, which are evaluated against 21 drifters that passed through the ACC meander. In this region, SWOT SSH remain balanced and valid for inferring surface velocities at scales as small as 10 km. For the original SWOT SSH, an optimal length scale of 26 km is identified as a trade-off between suppressing unbalanced signals and preserving finer-scale balanced motions. This optimal length scale is reduced to 18 km for the noiseless SWOT SSH. At these scales, geostrophic balance alone becomes insufficient and leads to a 10-20\% bias compared to drifter velocities in cyclonic eddies, which is effectively corrected by applying cyclogeostrophy to SWOT SSH. Finally, distance-averaged pair statistics calculated from drifter pairs and virtual particles reveal that SWOT accurately captures dispersion properties over the 5-200 km range, unveiling distinct dispersion patterns between large and small separation scales. This suggests that balanced motions dominate dispersion in this range. By capturing balanced dynamics with unprecedented accuracy, SWOT offers new opportunities to understand the impact of small-scales on tracer exchange in the ACC, and the Southern Ocean more broadly.