Observation of internal tides, nonlinear internal waves and mixing in the Lombok Strait, Indonesia

摘要

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 similar to 300 m. We confirmed the appearance of the non-linear internal tide with an amplitude of similar to 90 m at a fairly close distance (similar to 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 similar to[10(-6) -10(-7)] m(2) 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.