Exploring Submesoscale Processes and Internal Solitary Waves Using SWOT Data in the South China Sea

The South China Sea (SCS) is abundant with oceanic fine-scale processes (FPs) that have horizontal scales smaller than 50 km, but their spatial and seasonal characteristics remain insufficiently understood due to the scarcity of high-resolution observations covering large spatial ranges. In this study, FPs in the SCS are systematically explored based on the Surface Water and Ocean Topography (SWOT) satellite mission which provides sea surface height data with kilometer-scale resolution in wide swaths. By defining FP signals as those missed by nadir-looking altimeters but resolved by SWOT, we find that northeastern and western parts of the SCS are two hotspots of FPs. The FPs show larger root-mean-squared sea level anomalies (SLAs) in summer than winter in both regions. By combining independent ocean color remote sensing data, we identify submesoscale processes and internal solitary waves (ISWs) as two typical forms of FPs captured by SWOT. Some submesoscale processes with spatial scales of ∼20 km and SLA amplitudes of 2.0–8.0 cm are demonstrated to be submesoscale anticyclonic (cyclonic) eddies, which have positive (negative) SLAs and are accompanied by lower (higher) chlorophyll-a concentrations. With respect to the ISWs, they mainly occur in the northeastern SCS originating from the Luzon Strait, and propagate westward and southwestward. ISWs occur more frequently in summer than winter. Their SLA amplitudes range from 5 to 51 cm and generally decrease with the shallowing water depths. These results demonstrate that SWOT data have a good application prospect for studying the characteristics and dynamics of FPs in the SCS.