Determining Oceanic Internal Solitary Waves Properties from Surface Signatures captured by SWOT Observations

Internal solitary waves (ISWs) affect oceanic human activities and play an essential role in ocean mixing. Satellite observations provide a wide-ranging perspective for understanding ISWs. The surface current induced by ISWs can create rough and smooth regions on the sea surface due to the modulated roughness, presenting alternating bright and dark stripes in radar images. Moreover, the pressure distribution characteristic of ISWs creates surface solitons, leading to significant sea surface height anomalies in satellite altimetry. These signatures can be observed synchronously in a swath mode and high spatial resolution by surface water and ocean topography (SWOT) satellite, providing a unique new opportunity to understand both the surface and subsurface characteristics of ISWs. Numerous studies have established the correlation between the surface features and the ISWs parameters in the ocean interior, enabling the inversion of ISWs using remote sensing datasets. However, existing methods still require further improvement, as they are generated from specific assumptions and are highly dependent on the selection of ocean stratifications. By measuring surface divergence and surface height anomalies in laboratory experiments, this study establishes the relationship between surface features and internal characteristics of ISWs. The results reveal that both the strong nonlinearity and the effects of non-hydrostatic contribute significantly to the interpretation of ISWs' surface features, which pose challenges to the accurate retrieval of ISWs parameters. To address these problems, a fully nonlinear, non-hydrostatic method is developed and tested under different laboratory and oceanic conditions, demonstrating a precise connection between surface divergence, surface height anomaly and ISWs parameters. Based on this method, we use sea surface height anomalies and radar backscatter intensities provided by SWOT to perform the inversion. The results indicate that the combination of these two signatures enables accurate retrieval of ISWs parameters and the corresponding pycnocline depth, even if the real-time measurement of stratifications is not available. This study establishes a reliable method to understand ISWs in the global oceans and also provides insights into the challenge of separating ISWs signatures from other oceanic phenomena in SWOT observations.