Generation of Shoreward Nonlinear Internal Waves South of the Hainan Island: Synthetic Aperture Radar Observations and Numerical Simulations

Abstract

Nonlinear internal waves (NLIWs) are a class of nonsinusoidal, large-amplitude and high-frequency internal gravity waves, whose amplitude is large compared to the pycnocline depth, beyond the framework of linear theories (Helfrich & Melville, 2006). NLIWs are often observed in coastal oceans and marginal seas and have been shown to be essential in driving interior mixing, scattering and ducting acoustic modes, and transporting materials (

Progress on Generation of Nonlinear Internal Waves on the Northern Continental Shelf South of Hainan Island

“…Moreover, the satellite observation (Figure 3) captured the NLIWs when local barotropic tidal currents were very weak. A reasonable explanation for the occurrence of internal waves irrelevant to the local barotropic tidal current is that the Xisha Islands play a more critical role in generating the observed internal waves than the shelf break, as inferred in our previous study (Jia et al, 2021).…”

“…The transect I across NLIW1 passes through the moorings A and B. The transect II across NLIW2 passes through an area of the Xisha Islands where the body force for the K 1 tidal constituent in summer has a maximum force of 1.47 m 2 s -2 (see Figure 6a of Jia et al, 2021).…”

“…Moreover, the Richardson number-dependent parameterizations of turbulent closure (Pacanowski & Philander, 1981) were used to calculate the vertical viscosity 𝜈 𝑣 = 𝜈 0 (1+𝛼𝑅𝑖) 𝑛 + 𝜈 𝑏 and vertical diffusivity 𝜅 𝑣 = 𝜈 𝑣 1+𝛼𝑅𝑖 + 𝜅 𝑏 , where 𝑅𝑖 = 𝑁 2 (𝑧)/(𝑢 2 𝑧 + 𝑣 2 𝑧 ) is the Richardson number, 𝑢(𝑣) is zonal (meridional) velocity, and 𝑁 is the buoyancy frequency. The parameters 𝜈 𝑏 , 𝜅 𝑏 , 𝛼, 𝑛 and 𝜈 0 , as well as the horizontal viscosity 𝜈 ℎ and diffusivity 𝜅 ℎ , were same as those detailed in Jia et al (2021), where…”

“…The northern continental shelf south of Hainan Island in the South China Sea (SCS) represents one such example. Based on the SAR observation and theoretical analysis, our preliminary study (Jia et al, 2021) has suggested that the NLIWs observed on the northern continental shelf south of Hainan Island (Figure 1) are generated from the Xisha Islands; however, in situ observation and numerical simulation are lack in the study. Therefore, the exploration for the generation of the NLIWs on the northern continental shelf south of Hainan Island is insufficient.…”

A Directional Decomposition Method to Estimate the Reflection and Transmission of Nonlinear Internal Waves Over a Slope

“…Nonlinear internal waves (hereafter NLIWs) are a ubiquitous oceanic phenomenon in the continental slope region around the world, for example, in the northern South China Sea (Alford et al., 2015; Jia et al., 2021; Klymak et al., 2011), the Oregon continental slope (Martini et al., 2013), the West Shetland slope (Hall et al., 2011, 2013), etc. NLIWs play an important role in mass transport and ocean mixing on continental slopes, through wave transmission, reflection, and breakdown into turbulence (Eriksen, 1982; Gilbert & Garrett, 1989; Munk & Wunsch, 1998; Wunsch, 1968).…”