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Indonesian seas have been known as the hotspot for internal waves (IWs) generation sites. The sinking tragedy of the Indonesian Naval Submarine, KRI Nanggala 402 on 21 April 2021 in the northern Bali Sea was highlights the need of detecting, mapping, and characterizing internal waves in Indonesian waters are compulsory mainly in the Indonesian Archipelago Sea Lanes (IASLs). IASLs is a gateway for sea crossings which can be used by civil navigations, intercontinental trade, and foreign military. This study focused on mapping the distribution and characteristics of internal waves qualitatively using EA 600 Single beam Echosounder (SBES) of the Indonesian Naval Vessel, KRI Rigel 933 during The Jala Citra Expedition 2-2022 Banda. The measurements were conducted around the IASLs route in the Bali Waters, Banda Waters and Buru Waters. The results show that the typical highfrequency non-linear internal waves (HFNWs) with an amplitude of less than 10 m were observed intermittently during the expedition, detected mostly in the narrow passages, rough topography and shallowing waters. Typical characteristics of internal solitary waves (ISWs) were also observed with typical amplitudes of ~20 - 65 m. An ISWs extreme events found in this study verified the "turbulent water" that was reported in in the IASLs around the Underwater Seamount (US) Nieuwerkerk waters, in 1925 during the Snellius Expedition. The detection of internal wave events using acoustic equipment, the single beam echosounder is considered effective which can later be used as the guidance for marine activities in the water column. [ABSTRACT FROM AUTHOR]

The Sulawesi Sea is one of the most active regions where internal solitary waves (ISWs) are frequently observed through satellite images. These waves that result from the nonlinear evolution of internal tides are generated over the Sibutu Sills and propagate over a long distance, up to 700 km before shoaling in coastal areas. To date there is yet no specific in-situ observation or numerical studies dedicated to characterize their dynamics. We present results from the combination of two simulations and in-situ observations which allow to describe the full life cycle from generation to breaking of ISWs in the Sulawesi Sea. A first set of 2D non-hydrostatic numerical simulations reproduces the generation of ISW from the non-linear steepening of the internal tides. The tidal energy flux emanated from the generation site is of about 15 kW m−1 with progressive decrease in the along flux direction resulting the growth of ISWs. The ISW energy flux increases up to large fraction of 32% of the total energy flux at 700 km from the generation point while the M 2 internal tide contributes to 64% of the total energy flux. A second simulation at higher resolution focusing on the shallow coastal area of the Manado Bay reproduces the breaking of the ISWs at the shelf slope and was compared with in-situ observations. About 3.5% of the energy contained in an ISWs packet is dissipated over a 3 km wide cross shelf region of the Manado Bay in the simulation. Both simulations and observations revealed the presence of energetic boluses identified as a sequence of high-frequency waves of elevations in the stratified bottom layer. A high level of turbulence was diagnosed in the observations and simulations from the Thorpe Method. The mean eddy kinetic energy dissipation rate and vertical diffusivity in the observation reaches as 10−6 W kg−1 and 10−3 m2 s−1, respectively; while the dissipation rate is one order of magnitude higher and the vertical diffusivity is one order lower in the model. This discrepancy likely reflects the sparse sampling in the observations as well as differences in the stratification and the absence of surface forcing in the model. • Southeastward internal solitary waves in the Sulawesi Sea are formed through nonlinear evolution of internal tides. • Non-hydrostatic model is capable of estimating the efficiency of internal solitary waves in pumping internal tide energy. • Thorpe method is applied to estimate the dissipation rate from observation and model. • Energetic boluses are identified as running upslope of high-frequency waves following the breaking event of solitary waves. [ABSTRACT FROM AUTHOR]

Lombok Strait is one of the main exit passages of the Indonesian throughflow (ITF), connecting the interior Indonesian seas with the Indian Ocean. Satellite images have shown that this strait is also the most remarkable zone of the Indonesian seas for the generation of internal tides, which frequently evolve into internal solitary waves (ISWs). Here we present the first comprehensive high-frequency observations of the internal tide in the strait. The observations were carried out at a fixed position around 8 km from the western coast of Lombok Island at a depth of ~300 m. We confirmed the appearance of the non-linear internal tide with an amplitude of ~90 m at a fairly close distance (~30 km) from its generation site in the Nusa Penida Sills (NPS), with a dominant M 2 tidal frequency. High-frequency internal waves associated with vertical velocities reaching 20 cm s-1 were observed within the internal tidal trough. We estimated the turbulent kinetic energy dissipation rate using Thorpe and Ellison scales and found a mean dissipation rate of the order of ~ [10-6-10-7] m2 s-3, with enhanced values in the thermocline layer, possibly driven by shear instabilities. We underlined that the use of the Ellison scale is a promising alternative for indirectly estimating the dissipation rate from high-resolution time-series data sets. • CTD profiles and high frequency temperature measurements were used to estimate the turbulent dissipation rate. • Non-linear internal tide with dominant M 2 frequency appeared in the Lombok Strait. • High frequency internal waves were observed continuously within internal tidal troughs. • The improved Thorpe and the Ellison methods are utilized to estimate the dissipation rate. • Enhanced dissipation is induced when internal waves interact with the shore. [ABSTRACT FROM AUTHOR]