Three‐Dimensional Evolution of Internal Solitary Waves in the Northern South China Sea Revealed by SWOT Observations

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Abstract Utilizing 250‐m resolution sea surface height anomaly (SSHA) data from the Surface Water and Ocean Topography (SWOT) satellite in combination with mooring measurements, this research investigates the three‐dimensional evolution of internal solitary waves (ISWs) in the northern South China Sea (nSCS). A novel inversion method based on the horizontal momentum equation was developed to retrieve ISW amplitudes from SSHA data, yielding a mean absolute deviation of 16% relative to mooring measurements. Application of this method to ISW SSHA (5–60 cm) in the nSCS revealed ISW amplitude distributions spanning 10–250 m. A stratification‐modulated quasi‐linear correlation between amplitude and SSHA was identified in waters deeper than 1,000 m, with slope coefficients ranging from ∼350 (July–September) to ∼530 (January–March), enabling fast amplitude estimation from SWOT observations. SWOT's orbital configurations allow tracking of ISW evolution in the nSCS at daily intervals, revealing three key features of ISW evolution: (a) the total energy integrated along the ISW crest typically decreased, and the south‐strong–north‐weak asymmetry of the ISW crest generally reversed during the basin‐to‐slope propagation; (b) in addition to distorting the wave crest, mesoscale eddies are linked to ISW amplitude increases of up to 34% in energy convergence portions and decreases of up to 49% in energy divergence portions; (c) oblique interactions between ISWs generated near the Batan and Babuyan Islands notably enhanced the ISW amplitude. This research underscores the potential of combining SWOT and mooring data to better monitor ISW structure and understand their interactions with mesoscale features.

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