Surface Wave Breaking Caused by Internal Solitary Waves: Effects on Radar Backscattering Measured by SAR and Radar Altimeter

Abstract

Breaking surface waves play a key role in the exchange of momentum, heat, and gases between the atmosphere and the ocean. Waves break at the ocean’s surface at high or medium wind speeds or in the absence of wind due to shoaling of the seafloor. However, surface waves also break due to interactions with internal solitary waves (ISWs). In this paper, we revisit surface wave breaking caused by ISWs and how ISWs are manifested in synthetic aperture radar (SAR) images acquired by the TerraSAR-X and Sentinel-1 satellites and in high-resolution radar altimeter data acquired by the SAR altimeter (SRAL) onboard the Sentinel-3A satellite. X-band TerraSAR-X images acquired at low wind speeds suggest that meter-scale surface breaking waves resulting from large-scale ISWs are associated with large modulations in backscatter at HH and VV polarizations that cannot be explained by present theories. Furthermore, Sentinel-1 C-band SAR satellite images acquired at moderate to high wind speeds also exhibit large radar signatures from surface wave breaking at VV and VH cross-polarizations. Finally, new observations from the Sentinel-3 SRAL altimeter show clear evidence of significant wave height (SWH) variations along the propagation paths of ISWs. The SWH signatures are unique in showing that the surface wave energy does not return to its unperturbed level after an ISW passes, most likely because intense meter-scale wave breaking results in surface wave energy dissipation. In summary, these results show that surface wave breaking contributes significantly to radar remote sensing of ISWs.

Strongly Nonlinear Effects on Determining Internal Solitary Wave Parameters From Surface Signatures With Potential for Remote Sensing Applications

“…Figures 3d and 3e show that both the maximum values of u s and its divergence are directly proportional to the amplitude of ISWs (Vlasenko et al., 2000), which means that under the same oceanic conditions, the brighter or darker the stripes in the image indicate the larger amplitudes. However, the image intensity is sensitively influenced by environmental factors such as wind and surface waves (Magalhães, Alpers, et al., 2021), making it difficult to be widely quantitatively applied. Qualitative analysis (Magalhães & da Silva, 2012; Magalhães, Pires, et al., 2021) and more detailed sea surface dynamical modeling about the intensity will facilitate the acquisition of additional information from remote sensing.…”

The Surface Water and Ocean Topography Mission: A Breakthrough in Radar Remote Sensing of the Ocean and Land Surface Water

“…Since Seasat there have been numerous studies of internal solitary waves from radar as well as sunglint images over a wide range of locations of the world's oceans (Jackson, 2007; Magalhães et al., 2021). Through generation by interaction of tidal currents with bottom topography, these waves is tied to the local tidal cycle.…”

“…Although these energetic waves have been surveyed by spaceborne SAR over decades, SAR images of surface roughness do not have information on the magnitude of surface perturbations that are related to the energetics of the waves. Previous studies made inferences on the energy carried by these waves, suggesting possibly 10% of tidal dissipation could be accounted for by generating internal solitary waves over rough bottom topography (Magalhães et al., 2021). For the first time, SWOT will provide joint SAR images and elevation maps over these waves.…”

Observations of Tidal Modulation on Diurnal Vertical Displacements of the Oceanic Transition Layer

“…Therefore, in addition to wind‐induced LC, wind stress was also capable of generating breaking wave crests and directly injected turbulence into the water column (Dong et al., 2022; Wang et al., 2023). Together with onshore shoaling (Magalhães et al., 2021), these breaking waves resulted in relatively constant and very large TKE dissipation rates (∼10 −5 –10 −4 W/kg) between ∼5 and 10 m, which were 1–2 orders larger than those between ∼10 m and the ML base (Figure 2b) (Anis & Moum, 1995; Burchard et al., 2008; Terray et al., 1996; Thomson et al., 2016). Moreover, on 31 May and in the morning on 28 May, the TKE dissipation rate above ∼10 m clearly decreased as the wind relaxed.…”