Energetic And Dynamics Of Internal Tide Modulated By The Indopacific Circulation System

Internal tides are ubiquitous in the stratified ocean where barotropic tidal currents flow over various topographical features,including continental slopes,sea-mountains,ridges and submarine canyons.Internal tidal breaking and dissipation can induce strong diapycnal mixing both in local rough topographical features and deep basin areas,which is found to play an important role in sustaining global meridional overturning circulation.The background subtidal currents modulate the horizontally varying stratification,which could influence the generation and propagation of internal tides.The subtidal circulation fields vary significantly on different spatiotemporal scales,so their interactions with internal tides may change in time and space.We use a high-resolution numerical model to investigate the variability of M2 internal tides during their generation and propagation through the Indo-Pacific circulation system.We further detect the variability of internal tide evolution in different time scales.Special attention is directed to the seasonal and interannual variability of the local dissipation efficiency q.The variability and energetics of M2 internal tides during their generation and propagation through the Kuroshio flows northeast of Taiwan are investigated using a high-resolution numerical model.The corrugated continental slopes,particularly the I-Lan Ridge and Mien-Hua Canyon,are first identified as the energetic sources of M2 internal tides.The M2 internal tide generation is influenced by horizontally varying,zonally tilting stratification associated with the Kuroshio.In this situation,the conversion rate decrease by?30%at the I-Lan Ridge but increase within?10%at the Mien-Hua Canyon and north shelf,in comparison to the ideal simulation initiated with horizontal homogeneous stratification.Internal tides from multiple sources interfere to form a three-dimensional baroclinic field.An energetic along-slope tidal beam from the I-Lan Ridge radiates southward,against the northward Kuroshio flows,causing strong vertical displacement.Complex topographic features and background currents enhance the internal tide dissipation,which induces strong,inhomogeneous vertical mixingThe interaction between the energetic internal tides in the Indonesian Seas and the Indonesian Throughflow(ITF)is not well known.Here we conduct a series of high-resolution numerical simulations surrounding the Lombok Strait,Indonesia,which is an important exit channel for the ITF,to explore the influences of the ITF on the spatiotemporal variations of M2 internal tides generated from the Strait.The ITF enhances the north-south asymmetry of internal tide propagation from the Lombok Strait.Seasonal variations of internal tide generation are associated with the surface salinity variations induced by the monsoon and ITF.Interannual variability of internal tide generation and dissipation are due to ITF and air-sea freshwater flux induced stratification variations associated with El Nino-Southern Oscillation.The local dissipation efficiency q exhibits substantial seasonal and interannual variations,which may provide effective feedback to the climate processes in the low-latitude equatorial oceansWe further examines the effects of the South Equatorial Current(SEC)system on the generation and propagation of the M2 internal tides.We firstly investigate the dynamics and mechanism of the M2 internal tides in the Indo-Australian(IA)basin based on a high-resolution numerical model.M2 internal tides in the entire basin are originated from multiple source sites,including the Lombok Strait(LS),the region around Timor Island and Australian west shelf(AWS).In the near field of the LS,the Indonesian Throughflow modulates M2 internal tides generated energy.In the mid-field,M2 internal tides are refracted by the SEC system.After propagating across the SEC system,the remaining energy travels into the IA basin over a distance of?500km and finally arrives at the northwest slope of Australia.Another beam radiated from the AWS can interfere with this long-range beam from the LS,forming an inhomogeneous baroclinic field which can be reproduced by an improved line source model.The influence of the SEC system and multi-sources interference can increase internal tide dissipation,resulting in a nonuniform distribution.