Spectral Characteristics And Energy Distribution Of Internal Waves In The South China Sea Revealed By A Tidal-resolving Ultra-high Resolution Numerical Simulation

Internal waves are super-inertial waves occurring in the stably stratified ocean interior.According to its frequency or wavelength,internal waves can be categorized into near-inertial waves,internal tides,internal solitary waves and high-frequency nonlinear internal waves.Internal wave spectrum reflects energy distribution of internal wave field as a function of frequency and wavenumber,which plays an important role in the studies of nonlinear wave-wave interaction,acoustic propagation and the parameterization of turbulent dissipation and mixing.The South China Sea(SCS)is the largest marginal sea of the northwestern Pacific,which is populated by multi-scale ocean dynamic processes as a result of complex topography,tides,monsoon wind forcing and the Kuroshio intrusion through the Luzon Strait(LS).Frequent occurrences of internal tides and internal solitary waves make the SCS one of the most energetic regions of internal waves in the world's oceans.Using data from mooring observations and a tidal-resolving ultra-high resolution numerical simulation(the so-called llc4320),we analyzed the frequency-wavenumber spectra characteristics of internal waves in the SCS,and its relation with the universal Garrett-Munk spectrum for the internal wave fields in the open ocean(hereafter referred to as the GM spectrum).The results show that the llc4320 simulations successfully capture main characteristics of internal wave spectra in different regions of the SCS.The total wave energy appears to decay with the distance from the generation sites of internal waves(it ranges from 0.7 to 6.3 times of that for the GM spectrum).We further investigated the spatial distribution and seasonal variation of internal wave energy in the SCS.The SCS-GM spectrum is proposed to describe the average level of internal wave fields in the SCS.The results indicate that internal wave energy is heterogeneous with spatial variations of several orders of magnitude in intensity.The average relative intensity can reach 16.9 in the LS region,but only 2.5 in the SCS region.Moreover,internal wave energy is much higher in summer than other seasons due to the stronger stratification.